2007_美国_AAR0706.pdf

8 Runway Overrun and Collision Southwest Airlines Flight 1248 Boeing 737-7H4, N471WN Chicago Midway International Airport Chicago, Illinois December 8, 2005

〔图〕aviation\n ACCIDENT REPORT

NTSB/AAR-07/06

〔图〕NNATIONALAL3HVSBOARD\n National Transportation Safety Board

NTSB/AAR-07/06 PB2007-910407 Notation 7753F Adopted October 2, 2007

Aircraft Accident Report

Runway Overrun and Collision Southwest Airlines Flight 1248 Boeing 737-7H4, N471WN Chicago Midway International Airport Chicago, Illinois December 8, 2005

〔图〕L221ONAcOgAL3dVs\n

National

Transportation Safety Board

490 L'Enfant Plaza, S.W. Washington, D.C. 20594

National Transportation Safety Board. Year. Runway Overrun and Collision, Southwest Airlines Flight 1248, Boeing 737-7H4, N471WN, Chicago Midway International Airport, Chicago, Illinois, December 8, 2005. Aircraft Accident Report NTSB/AAR-07/06. Washington, DC.

Abstract: This report explains the accident involving a Boeing 737-7H4, N471WN, operated by Southwest Airlines (SWA), which departed the end of runway 31C after landing at Chicago Midway International Airport. The safety issues discussed in this report include the flight crew's decisions and actions, the clarity of assumptions used in on board performance computers, SWA policies, guidance, and training, arrival, landing distance assessments and safety margins, runway surface condition assessments and braking action reports, airplane-based friction measurements, and runway safety areas. Safety recommendations concerning these issues are addressed to the Federal Aviation Administration.

The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine, pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical reviews.

Recent publications are available in their entirety on the Web at . Other information about available publications also may be obtained from the Web site or by contacting:

National Transportation Safety Board

Records Management Division, CIO-40

490 L'Enfant Plaza, S.W.

Washington, D.C. 20594

(800) 877-6799 or (202) 314-6551

Safety Board publications may be purchased, by individual copy or by subscription, from the National Technical Information Service. To purchase this publication, order report number PB2007-910407 from:

National Technical Information Service

5285 Port Royal Road

Springfield, Virginia 22161

(800) 553-6847 or (703) 605-6000

The Independent Safety Board Act, as codified at 49 U.S.C. Section 1154(b), precludes the admission into evidence or use of Board reports related to an incident or accident in a civil action for damages resulting from a matter mentioned in the report.

AIRCRAFT Accident Report

CONTENTS

Abbreviations and Acronyms $\ldots$ vi

Executive Summary $\ldots$ ix

1. Factual Information $\ldots$ 1

1. 1 History of Flight $\ldots$ 1

1. 2 Injuries to Persons $\ldots$ 6

1. 3 Damage to Aircraft $\ldots$ 6

1. 4 Other Damage $\ldots$ 6

1. 5 Personnel Information .................................................................................................................................... 6

1. 5.1 The Captain $\ldots$ 6

1. 5.2 The First Officer $\ldots$ 7

1. 6 Aircraft Information $\ldots$ 8

1. 6.1 General $\ldots$ 8

1. 6.2 Southwest Airlines On Board Performance Computer 9

1. 7 Meteorological Information .................................................................................................... 9

1. 7.1 Chicago Midway International Airport Weather Information $\ldots$ 9

1. 7.2 Flight Crew Dispatch and In-Flight Weather Information. 10

1. 8 Aids to Navigation $\ldots$ 11

1. 9 Communications $\ldots$ 11

1. 10 Airport Information $\ldots$ 11

1. 10.1 Chicago Midway International Airport Winter Operations – General .................................... 13

1. 10.2 Chicago Midway International Airport Winter Operations on the Day of the Accident $\ldots$ 14

1. 10.3 Chicago Midway International Airport Runway Safety Areas .................................................................... 14

1. 11 Flight Recorders $\ldots$ 16

1. 11.1 Cockpit Voice Recorder $\ldots$ 16

1. 11.2 Flight Data Recorder $\ldots$ 16

1. 11.3 Flight Data Recorder Information From Other Landing Airplanes $\ldots$ 17

1. 12 Wreckage and Impact Information $\ldots$ 18

1. 13 Medical and Pathological Information $\ldots$ 18

1. 14 Fire $\ldots$ 19

1. 15 Survival Aspects $\ldots$ 19

1. 16 Tests and Research. 19

1. 16.1 Airplane Simulation and Performance Studies $\ldots$ 19

1. 17 Organizational and Management Information $\ldots$ 21

1. 17.1 Southwest Airlines Information $\ldots$ 21

1. 17.2 Southwest Operations Guidance Information $\ldots$ 21

1. 17.2.1 Thrust Reverser Procedures and Information $\ldots$ 21

1. 17.2.2 Autobrake Procedures and Information $\ldots$ 23

1. 17.2.3 On Board Performance Computer-Related Guidance and Information 23

1. 17.2.4 Mixed Braking Action Report and Tailwind Limitation Guidance 28

1. 17.3 Southwest Airlines Postaccident Actions $\ldots$ 29

1. 18 Additional Information $\ldots$ 29

1. 18.1 Airplane Landing Performance Information $\ldots$ 29

Contents

AIRCRAFTAccident Report

1. 18.1.1 Previously Issued Urgent Safety Recommendation Related to Landing Distance Assessments $\ldots$ 30

1. 18.1.2 Landing Distance Assessment Technical Bulletin $\ldots$ 33

1. 18.2 Contaminated Runway and Landing Information $\ldots$ 35

1. 18.2.1 Runway Surface Condition Reports $\ldots$ 35

1. 18.2.2 Correlation Between Runway Surface Condition and Airplane Braking Ability $\ldots$ 35

1. 18.2.3 Previous Contaminated Runway-Related Safety Recommendations $\ldots$ 38

1. 18.3 Previous Runway Safety Area Safety Recommendations $\ldots$ 41

2. Analysis $\ldots$ 43

1. 1 $\text{ General}$ $\ldots$ 43

1. 2 Pilots' Decision to Land, Knowledge, and Actions $\ldots$ 44

1. 2.1 Interpretation and Use of Mixed Braking Action Reports $\ldots$ 44

1. 2.2 On Board Performance Computer Displays and Underlying Assumptions $\ldots$ 46

1. 2.3 Thrust Reverser Usage and Autobrakes $\ldots$ 49

1. 3 Landing Distance Assessments $\ldots$ 52

1. 3.1 Preflight and Arrival Landing Distance Calculations/Assessments $\ldots$ 53

1. 3.2 Safety Alert for Operators Discussion and Industry Practice

Regarding Landing Distance Assessments $\ldots$ 55

1. 3.3 Landing Distance Assessments Summary $\ldots$ 56

1. 4 Runway Surface Condition Assessments $\ldots$ 58

1. 4.1 Braking Action Reports $\ldots$ 58

1. 4.2 Contaminant Type and Depth $\ldots$ 59

1. 4.3 Airport Runway Surface Friction Measuring Devices $\ldots$ 60

1. 4.4 Runway Surface Condition Assessments Summary $\ldots$ 60

1. 4.5 Correlating Runway Surface Condition to Airplane Landing Performance $\ldots$ 61

1. 5 Airplane-Based Friction Measurements $\ldots$ 62

1. 6 Runway Safety Areas $\ldots$ 63

3. Conclusions $\ldots$ 65

1. 1 Findings $\ldots$ 65

1. 2 Probable Cause $\ldots$ 67

4. Recommendations $\ldots$ 68

1. 1 New Recommendations $\ldots$ 68

1. 2 Previously Issued Recommendation Resulting From This Accident Investigation and Classified in this Report $\ldots$ 69

5. Appendix $\ldots$ 70

A: Investigation and Public Hearing $\ldots$ 70

B: Cockpit Voice Recorder $\ldots$ 71

C: FAA Safety Alert For Operators 06012 $\ldots$ 225

AIRCRAFT Accident Report

FIGURES

1. Photograph of the accident airplane in the roadway intersection. 4

1. Diagram showing the accident airplane where it came to rest (on a heading of 340°) in the intersection off the end of runway 31C. 5

1. The MDW airport layout plan with surrounding streets and properties. .................................... 12

1. OPC display showing the results of OPC calculations based on the accident conditions with fair braking action. 26

1. OPC display showing the results of OPC calculations based on the accident conditions with poor braking action. 27

1. Draft winter operations guide that was developed by an industry group. .................................................. 34

1. CRFI values for various runway surface conditions. $\ldots$ 37

AIRCRAFTAccident Report

ABBREVIATIONS AND ACRONYMS

AC advisory circular

ACM airport certification manual

agl above ground level

ARFF aircraft rescue and firefighting

ASOS automated surface observing system

ASRS aviation safety reporting system

ATC air traffic control

ATCT air traffic control tower

ATIS automatic terminal information service

ATP airline transport pilot

BWI Baltimore/Washington Thurgood Marshall International Airport

C Celsius

CFME continuous friction measurement equipment

CFR Code of Federal Regulations

CRFI Canadian Runway Friction Index

CVR cockpit voice recorder

DEC decelerometer

DOA Department of Aviation

DOT Department of Transportation

EASA European Aviation Safety Agency

Abbreviations and Acronyms

AIRCRAFTAccident Report

EFB electronic flight bag

EMAS engineering materials arresting system

F Fahrenheit

FAA Federal Aviation Administration

FAR Federal Aviation Regulations

FDR flight data recorder

FOM flight operations manual

FRM flight reference manual

Hg inch of Mercury

ICAO International Civil Aviation Organization

ILS instrument landing system

IRFI International Runway Friction Index

JAA Joint Aviation Authorities

JWRFMP Joint Winter Runway Friction Measurement Program

MDW Chicago Midway Airport

mm millimeter

msl mean sea level

MU coefficient of friction

N1 engine fan speed

NASA National Aeronautics and Space Administration

NWS National Weather Service

OPC on board performance computer

Abbreviations and Acronyms

AIRCRAFT Accident Report

AIRCRAFT Accident Report

EXECUTIVE SUMMARY

On December 8, 2005, about 1914 central standard time, Southwest Airlines (SWA) flight 1248, a Boeing 737-7H4, N471WN, ran off the departure end of runway 31C after landing at Chicago Midway International Airport, Chicago, Illinois. The airplane rolled through a blast fence, an airport perimeter fence, and onto an adjacent roadway, where it struck an automobile before coming to a stop. A child in the automobile was killed, one automobile occupant received serious injuries, and three other automobile occupants received minor injuries. Eighteen of the 103 airplane occupants (98 passengers, 3 flight attendants, and 2 pilots) received minor injuries, and the airplane was substantially damaged. The airplane was being operated under the provisions of 14 Code of Federal Regulations Part 121 and had departed from Baltimore/Washington International Thurgood Marshall Airport, Baltimore, Maryland, about 1758 eastern standard time. Instrument meteorological conditions prevailed at the time of the accident flight, which operated on an instrument flight rules flight plan.

The National Transportation Safety Board determined that the probable cause of this accident was the pilots' failure to use available reverse thrust in a timely manner to safely slow or stop the airplane after landing, which resulted in a runway overrun. This failure occurred because the pilots' first experience and lack of familiarity with the airplane's autobrake system distracted them from thrust reverser usage during the challenging landing.

Contributing to the accident were Southwest Airlines' 1) failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations; 2) programming and design of its on board performance computer, which did not present inherent assumptions in the program critical to pilot decision-making; 3) plan to implement new autobrake procedures without a familiarization period; and 4) failure to include a margin of safety in the arrival assessment to account for operational uncertainties. Also contributing to the accident was the pilots' failure to divert to another airport given reports that included poor braking action and a tailwind component greater than 5 knots. Contributing to the severity of the accident was the absence of an engineering materials arresting system, which was needed because of the limited runway safety area beyond the departure end of runway 31C.

The safety issues discussed in this report include the flight crew's decisions and actions, the clarity of assumptions used in on board performance computers, SWA policies, guidance, and training, arrival landing distance assessments and safety margins, runway surface condition assessments and braking action reports, airplane-based friction measurements, and runway safety areas.

AIRCRAFT Accident Report

1. FACTUAL INFORMATION

1.1 History of Flight

On December 8, 2005, about 1914 central standard time,$^{1}$ Southwest Airlines (SWA) flight 1248, a Boeing 737-7H4, N471WN, ran off the departure end of runway 31 center (31C) after landing at Chicago Midway International Airport (MDW), Chicago, Illinois. The airplane rolled through a blast fence, an airport perimeter fence, and onto an adjacent roadway, where it struck an automobile before coming to a stop. A child in the automobile was killed, one automobile occupant received serious injuries, and three other automobile occupants received minor injuries. Eighteen of the 103 airplane occupants (98 passengers, 3 flight attendants, and 2 pilots) received minor injuries, and the airplane was substantially damaged. The airplane was being operated under the provisions of 14 Code of Federal Regulations (CFR) Part 121 and had departed from Baltimore/Washington International Thurgood Marshall Airport (BWI), Baltimore, Maryland, about 1758 eastern standard time. Instrument meteorological conditions prevailed at the time of the accident flight, which operated on an instrument flight rules flight plan.

The accident occurred on the first flight of the first day of a scheduled 3-day trip. The flight departed BWI about 2 hours late because of deteriorated weather conditions in the Chicago area. The captain was the flying pilot for the accident flight, and the first officer performed the duties of the monitoring pilot.

The pilots reported that they had thoroughly reviewed the two weather information and dispatch documents they received from dispatch before they left BWI. A third document authorizing the release of the accident flight was prepared but was not delivered to the pilots before departure. This document revised the expected landing winds (from “�alm” to “090° at 11 knots”), runway braking action (from “wet-good” to “wet-fair”), and landing runway (from 04R to 31C) based on the changing weather. The pilots stated that they subsequently received updated MDW weather information and runway condition/braking action reports $^{2}$ for runway 31C, which was the runway in use at MDW at the time. Postaccident interviews with the pilots and evidence from cockpit voice recorder (CVR)$^{3}$ data and air traffic control (ATC) communications indicated that the runway 31C braking action reports were mixed, reporting good or fair braking action for the first half of the runway and poor braking action for the second half.

Factual Information

AIRCRAFT Accident Report

The pilots also stated (and CVR evidence confirmed) that they reviewed and discussed the company's new autobrake system procedures while en route from BWI to MDW; the accident landing was the first time either pilot landed using autobrakes.$^{4}$

About 1833:17, as the airplane was nearing MDW at an assigned altitude of 10,000 feet,$^{5}$ ATC issued the pilots instructions to enter a holding pattern. (ATC indicated that the hold was because of runway-clearing snowplow operations at MDW.) About 1844:04, the pilots advised ATC that they were entering the holding pattern at 10,000 feet. The first officer stated that, while in the holding pattern, he entered the updated weather and runway conditions and wind information (090° at 11 knots) in the on board performance computer (OPC)$^{6}$ to determine the landing distance required for runway 31C. The reported wind conditions resulted in a computed tailwind component of 8 knots.$^{7}$ All SWA 737s are limited to landing with a 10-knot or less tailwind component under all runway surface conditions. Additionally, SWA policies and flight operations manuals indicate that the company does not authorize landings on runways with more than a 5-knot tailwind component with poor braking action. Postaccident statements and CVR evidence indicated that the accident pilots were aware of these limitations and believed that they would be unable to land at MDW if the braking action was reported poor for the full length of the runway.

The first officer entered multiple scenarios into the OPC, entering fair and poor pilot braking action reports separately because the OPC was not designed to accept mixed braking action report inputs. Based on the first officer's inputs, the OPC estimated that the airplane would stop about 560 feet before the departure end of the runway with fair braking action and about 40 feet before the departure end of the runway with poor braking action.$^{8}$ The pilots stated that they decided that, consistent with SWA policies, they

Factual Information

AIRCRAFT Accident Report

would divert to one of their alternate destinations (Kansas City or St. Louis, Missouri)$^{9}$ if the tailwind component increased to above 10 knots or if pilot braking action reports indicated poor braking action for the full length of the runway. The automatic terminal information service (ATIS) reported a runway visual range (RVR)$^{10}$ for runway 31C of about 5,000 feet.

About 1854:10, ATC began providing the pilots with radar vectors and descent instructions as they departed the holding pattern for the final approach course for the instrument landing system (ILS) approach to runway 31C. At that time, the RVR was reported as 4,500 feet variable to 5,000 feet,$^{11}$ and the ATIS was reporting winds from 100° at 11 knots. About 1903:44, ATC cleared the pilots to intercept the runway 31C localizer. Less than a minute later, ATC cleared them for the approach and advised that the braking action reported for runway 31C was “fair except at the end [it’s]...poor.”

According to the CVR transcript, when the pilots contacted the MDW Air Traffic Control Tower (ATCT) at 1909:53.7, controllers advised them to “continue for [runway] 31C the winds zero nine zero at nine, brakin’ action reported good for the first half, poor for the second half.” About 1912:28, the first officer received a landing clearance from the ATCT. Flight data recorder (FDR) data indicated that the airplane was aligned on the runway centerline as it touched down at an airspeed of about 124 knots. The speed brakes deployed and brake pressure increased within about 1 second. Both pilots described the touchdown as “firm.”

The captain stated that he tried to deploy the thrust reversers immediately after touchdown but had difficulty moving the thrust reverser levers to the reverse thrust position. He further stated that he felt the antiskid system cycle after the airplane touched down but then felt it stop cycling and that the airplane seemed to accelerate. He said that he subsequently applied the wheel brakes manually but made no further effort to activate the thrust reversers. He told investigators that he believed that the use of the autobrake system distracted his attention from the thrust reversers after his initial attempt to deploy them.

The first officer said that, when he sensed a decrease in the airplane's deceleration during the landing sequence, he exclaimed, "brakes, brakes, brakes," and manually applied the brakes. He stated that he then looked at the throttle console and saw that the thrust reverser levers were still in the stowed position. The first officer moved the captain's hand away from the thrust reverser levers and, about 15 seconds after touchdown, initiated deployment of the thrust reversers to the maximum reverse setting. FDR evidence

Factual Information

AIRCRAFT Accident Report

confirmed the systems functions described by the pilots and indicated that full thrust reverser deployment occurred about 18 seconds after touchdown.

However, the airplane ran off the departure end of runway 31C and continued through the runway safety area (RSA),$^{12}$ a blast fence, a navigational aid antenna, across an airport road, through an airport perimeter fence, and onto an adjacent public roadway. The airplane struck a northbound automobile on that roadway before it came to rest near an intersection located on the northwest corner of the airport. (Figures 1 and 2 show the airplane's position off the end of runway 31C.)

The first officer stated that, after the airplane came to a rest, he performed the emergency evacuation checklist while the captain checked on the passengers in the cabin. The passengers evacuated through the forward left and the right rear cabin doors.

〔图〕55505F034\n

Figure 1. Photograph of the accident airplane in the roadway intersection. (Looking southeast, towards the departure end of runway 31C.)

Factual Information

AIRCRAFTAccident Report

〔图〕NYH 3④④串串G N女女④FOUND RED PAINT ON TOP OF CURBC RUNAY CROSS SEOTION AUCNMENT④SCARSNOEs OUD D NOUTSOE EDGE ORON SNOWAPPROA

Figure 2. Diagram showing the accident airplane where it came to rest (on a heading of 340°) in the intersection off the end of runway 31C.

Factual Information

AIRCRAFT Accident Report

1.2 Injuries to Persons

Table 1. Injury chart.

Note: Title 14 CFR 830.2 defines a serious injury as any injury that (1) requires hospitalization for more than 48 hours, starting within 7 days from the date that the injury was received; (2) results in a fracture of any bone, except simple fractures of fingers, toes, or the nose; (3) causes severe hemorrhages or nerve, muscle, or tendon damage; (4) involves any internal organ; or (5) involves second- or third-degree burns or any burns affecting more than 5 percent of the body surface. A minor injury is any injury that does not qualify as a fatal or serious injury.

1.3 Damage to Aircraft

The airplane had substantial, repairable damage.

1.4 Other Damage

The airplane rolled through an airport blast fence, an ILS array, a frangible airport perimeter fence, and onto a roadway, where it struck an automobile and a fire hydrant. Damage to the wing leading edges and engine nacelles of the airplane aligned with vertical posts from the airport perimeter fence; there was no damage observed in the airplane cockpit or cabin.

1.5 Personnel Information

1.5.1 The Captain

The captain, age 59, was a pilot in the U.S. Air Force for 26 years before he was hired by SWA on August 3, 1995. He was hired as a first officer and was upgraded to captain in July 2000. The captain held a multiengine airline transport pilot (ATP) certificate with a type rating in the Boeing 737. The captain held a first-class Federal Aviation Administration (FAA) airman medical certificate, dated September 21, 2005, with the limitation that he “must wear corrective lenses.”$^{13}$

According to the captain's SWA employment and flight records, he had flown about 15,000 hours total flight time, including 9,500 hours as pilot-in-command, about

Factual Information

AIRCRAFTAccident Report

4,500 hours of which were in 737 airplanes. He had flown about 198, 137, 58, 14, and 2 hours in the 90, 60, 30, and 7 days and 24 hours, respectively, before the accident. Company records showed that the captain obtained his initial 737 type rating in May 1995 and that his most recent line check, proficiency check, and recurrent training occurred in June and July 2005. A search of FAA records revealed no accident or incident history, enforcement action, or pilot certificates and ratings failure or retest history. A search of the National Driver Register found no record of driver's license suspension or revocation.

The captain had not flown for the 4 days before the accident flight. He told investigators that he slept well the night before the accident and commuted to BWI from his home in Buffalo, New York, arriving at BWI about 1235. The accident airplane was pushed back from the gate about 1650 for its departure to MDW.

During postaccident interviews, the captain stated that the weather on the accident night was the worst he had experienced but that he expected to be able to land safely and uneventfully. He estimated that he had landed when the runway conditions were poor because of winter weather about 12 to 15 times during his tenure with SWA. However, he indicated that there was never a time previously when he thought he would not be able to stop before the end of the runway. The captain further told investigators that he had not previously used the autobrake system during a simulator or airplane landing.

1.5.2 The First Officer

The first officer, age 34, was a Saab 340 pilot for Mesaba Airlines for 6 years (2 years as first officer, 4 years as captain) before he was hired by SWA as a 737 first officer on February 17, 2003. He held a multiengine ATP certificate with a type rating in the 737. The first officer held a first-class FAA airman medical certificate, dated October 18, 2005, with the limitation that he “must wear corrective lenses.”$^{14}$

According to the first officer's SWA employment and flight records, he had flown about 8,500 hours total flight time, including 4,000 hours as pilot-in-command and about 2,000 hours as second-in-command in 737 airplanes. He had flown about 243, 151, 83, 8, and 2 hours in the 90, 60, 30, and 7 days and 24 hours, respectively, before the accident. Company records showed that the first officer obtained his initial 737 type rating in November 2001 and his most recent 737 proficiency check and recurrent training occurred in February 2005. A search of FAA records revealed no accident or incident history, enforcement action, or pilot certificate or rating failure or retest history. A search of the National Driver Register found no record of driver's license suspension or revocation.

The first officer was assigned to a reserve line of flying at the time of the accident, and checked in for reserve duty at BWI about 1040 on December 8. He told investigators that he had about 8 hours of sleep the night before and took a nap the day of the accident flight.

Factual Information

AIRCRAFTAccident Report

During postaccident interviews, the first officer stated that he had extensive experience with weather conditions similar to those they encountered on the night of the accident, although most of that experience was before he was hired by SWA. He stated that he had only landed in snow a few times since he was hired by SWA, and, in those instances, “nothing unusual occurred.” The first officer further told investigators that he had not previously used the autobrake system during a simulator or airplane landing.

1.6 Aircraft Information

1.6.1 General

The accident airplane, serial number 32471, was manufactured by Boeing and received its FAA airworthiness certificate on July 13, 2004. At the time of the accident, the airplane had accumulated about 5,273 total flight hours and 2,901 cycles.$^{15}$ The airplane was equipped with two CFM International$^{16}$ CFM56-7B24 turbofan engines, both of which were new when the airplane was delivered to SWA.

According to flight dispatch information, the airplane's actual takeoff weight for the accident flight was 129,000 pounds; the FDR recorded an actual MDW landing weight of 118,280 pounds. (The pilots used an estimated landing weight of 119,700 pounds in their OPC stopping margin calculations.) Airplane documentation indicates that the maximum structural takeoff and landing weights are 154,500 and 128,000 pounds, respectively.

Each of the airplane engines is equipped with a hydraulically actuated thrust reverser system, which is used to slow the airplane after landing. When the thrust reversers are deployed, blocker doors change the direction of the engine fan air exhaust, moving it outward and forward to create reverse thrust. The thrust reversers are operated by levers located on the forward side of the thrust levers on the throttle quadrant. Postaccident examination of the thrust reverser components from the accident airplane revealed no evidence of preimpact anomaly.

The 737-700 autobrake system is designed to automatically apply brakes upon main landing gear strut compression and wheel spinup after touchdown. The system senses deceleration during the landing roll and automatically modulates brake pressure accordingly. Postaccident examination of the autobrake system components from the accident airplane revealed no evidence of preimpact anomaly.

Factual Information

AIRCRAFT Accident Report

1347 on December 8 and ending about 0126 on December 9, 2005, with about 10 inches of total snow accumulation.

An official weather observation recorded at MDW about 1853 indicated winds from 100° at 11 knots; visibility 1/2 statute mile (sm) in moderate snow and freezing fog; ceiling broken at 400 feet above ground level (agl) and overcast at 1,400 feet agl; temperature minus 3° Celsius (C) (28° Fahrenheit [F]); dew point temperature minus 4° C (23° F); altimeter setting 30.06 inches of Mercury (Hg). Remarks: automated observation system, runway 31C 10-minute-averaged RVR 4,500 feet, snow increment 1 inch new snow last hour, 10 inches total, hourly liquid precipitation less than 0.01 inch (trace). As previously noted, according to postaccident interviews with ATC personnel, the ILS to runway 31C was the only approach available to commercial flights landing at MDW on the night of the accident because of approach visibility requirements.

A special weather observation recorded at MDW after the accident (at 1937) indicated winds from 160° at 5 knots; visibility 1/4 sm in heavy snow and freezing fog; sky condition obscured vertical visibility 200 feet; temperature minus 3° C (28° F); dew point temperature minus 4° C (23° F); altimeter setting 30.05 inches Hg. Remarks: automated observ[ing] system, runway 31C 10-minute-averaged RVR 3,000 feet.

Weather observations at MDW are made by an automated surface observing system (ASOS). The 5-minute observations surrounding the time of the accident indicated the following conditions:$^{19}$

· Weather observation at 1910: winds from 110° at 8 knots, visibility 1/2 mile in moderate snow and freezing fog, ceiling broken at 400 feet agl, overcast at 1,400 feet agl, temperature minus 4° C, dew point temperature minus 5° C, altimeter 30.06 inches Hg. Remarks: runway 31C visual range 4,500 feet variable 5,000 feet, hourly precipitation less than 0.01 inches.

· Weather observation at 1915: winds from 110° at 7 knots, visibility 1/2 mile in moderate snow and freezing fog, sky obscured vertical visibility 300 feet, temperature minus 4° C, dewpoint temperature minus 5° C, altimeter 30.06 inches Hg. Remarks: runway 31C visual range 4,500 feet variable 5,000 feet, hourly precipitation less than 0.01 inches.

1.7.2 Flight Crew Dispatch and In-Flight Weather Information

SWA records indicated that the airplane's original dispatch release was revised three times before the accident flight. Examination of these documents indicated that the revisions resulted from changes in alternate airport destinations, the contingency fuel load, and the planned landing runway at MDW. The accident flight's release calculations were based on the use of runway 31C. The release included two alternate airport destinations and enough fuel for the most distant alternate plus 90 minutes of contingency fuel.

Factual Information

AIRCRAFT Accident Report

The MDW forecast information in the dispatch paperwork was issued by the NWS about 1515 on December 8 and was considered valid from 1500 that day to 1200 on December 9. This forecast indicated the following conditions after 1500: winds from 080° at 11 knots, visibility 1/2 sm in moderate snow and freezing fog, overcast ceiling at 400 feet agl; temporarily between 1500 and 1600, visibility 1/4 sm in moderate snow and freezing fog, sky obscured vertical visibility 200 feet. After 1600, winds from 070° at 8 knots, visibility 1 sm in light snow and mist, ceiling overcast at 500 feet agl; temporarily between 1600 and 1900 visibility 1/2 sm in moderate snow and freezing fog, sky obscured vertical visibility 400 feet. After 1900, winds from 050° at 7 knots, visibility 2 sm in light snow, ceiling overcast at 700 feet agl. After 2100, winds from 340° at 12 knots, visibility better than 6 sm in light snow, ceiling overcast at 2,500 feet agl, temporarily between 2100 and 0000, visibility 3 sm in light snow showers. Related NWS forecast information indicated that the arrival of the snow system could be slightly delayed but predicted a significant snow event for the area the afternoon and evening of the accident.

A subsequent terminal forecast issued about 1738 predicted the snow ending and higher ceilings and improved visibilities in the early morning of December 9, as the system moved out of the area.

1.8 Aids to Navigation

No problems with any navigational aids were reported.

1.9 Communications

No communications problems between the pilots and any of the air traffic controllers who handled the accident flight were reported.

1.10 Airport Information

MDW is located about 10 miles southwest of downtown Chicago at an elevation of about 620 feet in an area that includes residential, commercial, and industrial land uses. (Figure 3 shows the MDW airport layout plan with surrounding streets and properties. Runway 31C is highlighted in yellow.)

Factual Information

AIRCRAFTAccident Report

〔图〕tt-售10a4L6,779847948281144.8746362513OT85/e900.2406.26.529425001,000358/05828GRAPHC SCALE IN FEETOnginal Date:_Mar 23 19

Figure 3. The MDW airport layout plan with surrounding streets and properties. Runway 31C is highlighted in yellow.

Factual Information

AIRCRAFT Accident Report

The airport is owned by the City of Chicago and operated by the Chicago Department of Aviation (DOA). MDW has five runways, including one set of two parallel runways (4R/22L and 4L/22R) and one set of three parallel runways (13L/31R, 13C/31C, and 13R/31L). Runway 31C is 6,522 feet long by 150 feet wide and is made of grooved concrete. The usable landing distance for runway 31C is 5,826 feet.$^{20}$ Runway 31C is equipped with an ILS approach, a visual approach slope indicator system, and runway end identifier lights.

According to postaccident interviews with ATC personnel, the ILS approach to runway 31C was the only approach available to commercial flights landing at MDW on the night of the accident because of approach visibility requirements. When the accident pilots departed the holding pattern for the final approach to runway 31C, the RVR was reported as 4,500 variable to 5,000 feet. The approach visibility requirement for runway 13C was 1 sm, whereas the requirement for the ILS approach to runway 31C was 5/8 sm visibility or 3,000 feet RVR.

The FAA certified MDW as a 14 CFR Part 139 airport with Index D aircraft rescue and firefighting (ARFF) capabilities. Examination of FAA Airport Certification/ Safety Inspection records for MDW from the years 2003, 2004, and 2005 revealed no deficiencies.

1.10.1 Chicago Midway International Airport Winter Operations – General

The MDW 2005-2006 Snow Removal Manual provides an overview of the procedures used by the Chicago DOA for snow removal operations at MDW. According to this manual and MDW personnel, snow removal and anti-icing operations are conducted from runway end to runway end. During snow removal operations, an MDW airport operations supervisor is positioned in the ATCT to act as a liaison between air traffic controllers in the tower and snow removal teams on the field. This coordination effort is intended to optimize use of the runways and minimize delays. The operations supervisor receives pilot reports regarding field conditions and/or runway braking action from ATC and relays them to snow removal teams as necessary. The operations supervisor also maintains a handwritten “snow log” that documents the snow removal and runway friction test activities.

The FAA-approved Airport Certification Manual (ACM) for MDW states that the airport is responsible, in part, for monitoring runway conditions and pilot reports, snow and ice removal as necessary, and coordination with ATC, air carriers, and other airport users during snow and ice events. The ACM also specifies that the airport will conduct

Factual Information

AIRCRAFTAccident Report

friction tests on the active runway, or any other runway available for aircraft use, on a "frequent" basis during events involving freezing precipitation or snow.

1.10.2 Chicago Midway International Airport Winter Operations on the Day of the Accident

According to MDW officials, early on the day of the accident, the Chicago DOA had received adverse weather reports and initiated the notification and mobilization phases of the snow operations plan. Snow began falling at the airport about 1347, at which time snow removal operations commenced. Snow removal operations involved the use of runway brooms, snow plows, a snow blower, deice machines, and runway friction testing equipment.

According to postaccident interviews and documentation, runway 13C/31C had been cleared five times during the 5 1/2 hours of snowfall before the accident, most recently about 1845. Friction test logs indicated that runway 31C was friction-tested before this clearing about 1839, with resultant coefficient of friction (MU) $readings^{21}$ of .59/.45/.37 (average .47).$^{22}$ A friction test conducted about 1847 produced results of .72/.59/.68 (average .67). The most recent field conditions reported on the MDW Web site (which were updated about 1850) indicated that runway 31C had a trace to 1/16 inch of wet snow over 90 percent of its surface, with 10 percent of its surface clear and wet. A friction test conducted after the accident (about 1922) produced results of .41/.40/.38 (average .40).

1.10.3 Chicago Midway International Airport Runway Safety Areas

According to Advisory Circular (AC) 150/5300-13, change 7, “Airport Design,” the RSA for runway 13C/31C at MDW should have extended 1,000 feet beyond the runway ends and been 500 feet wide.$^{23}$ FAA documentation indicates that, at the time of the accident, the runway 31C RSA extended 82 feet beyond the end of the runway and was 500 feet wide. The FAA’s RSA determination for this runway, dated September 20, 2000, stated, “it does not appear practicable to achieve the RSA standards” because the runway could not be realigned on site, and the acquisition of land for an RSA would require relocation of Central Avenue, 55th Street, and many businesses and homes in the area. However, the FAA instructed the Chicago DOA to “explore all options to bring the RSAs into full conformance with FAA standards.”

Factual Information

AIRCRAFTAccident Report

In 2003, the FAA asked the Chicago DOA to assess enhancement measures for improving the RSAs at MDW. In May 2004, the city stated in a response letter that there were no alternatives for achieving a standard RSA at MDW. The letter also stated the following:

● The runway could not be shortened and still meet the aircraft operational requirements.

● Extending the RSA would require acquisition and major impact to surrounding commercial properties and residential neighborhoods, public roadways, and public utility infrastructure.

● [The use of an] EMAS [engineering materials arresting system] was assessed, but insufficient spacing existed for installation of EMAS without shortening the runway, thus reducing the operational capacity of the airport.

The letter concluded that RSA enhancement at MDW could be obtained incrementally by improvements such as relocation of light poles and service road signs within the RSA. According to MDW officials, the FAA made no further requests to the city for improvements to MDW RSAs, including the installation of shorter, nonstandard EMAS beds,$^{24}$ before the accident.

After the accident, in April 2006, the Chicago DOA sent a letter and an EMAS study to the FAA. The letter summarized options for improving the MDW RSAs and concluded that a nonstandard EMAS bed with a 35-foot setback could be installed at the end of runway 31C. Engineering calculations showed that the nonstandard arrestor bed would be capable of stopping a Boeing 737-700 weighing 102,400 pounds and rolling at a ground speed of up to 57 knots on a wet runway without the use of thrust reversers.

After the accident, the National Transportation Safety Board asked the EMAS system manufacturer to model the accident $scenario^{25}$ and estimate the effect a nonstandard EMAS installation off the end of runway 31C would have had on the accident sequence. The EMAS manufacturer estimated that an arrestor bed 229 feet long would fit in the overrun area off the end of runway 31C. The manufacturer's simulations predicted that, based on the accident airplane's estimated runway exit speed of 53 knots, a 737 landing under conditions similar to the accident airplane would continue 206 feet into the EMAS bed before stopping. The simulations indicated that the airplane could have been traveling as fast as 58 knots when it ran off the end of the runway and still stop within a 229-foot-long EMAS bed. The simulations indicated that a nonstandard EMAS installation would have stopped the accident airplane before it departed airport property.

Factual Information

AIRCRAFT Accident Report

After the accident, the FAA approved the installation of nonstandard EMAS beds at MDW, and MDW and City of Chicago officials began to work toward installation of nonstandard EMAS beds at the ends of runways 31C, 13C, 4R, and 22L. By early December 2006, the first portion (170 feet long and 170 feet wide) of an EMAS bed had been installed off the departure end of runway 31C, with an additional 40-foot-long portion planned. Airport and city officials indicated that the installation of EMAS beds at the ends of affected MDW runways would be completed before winter 2007, pending relocation of localizer antennas at the ends of runways 13C, 4R, and 22L.

1.11 Flight Recorders

1.11.1 Cockpit Voice Recorder

The accident airplane was equipped with a Honeywell model 6022 CVR, serial number (S/N) CVR120-05823. The CVR showed no signs of damage and was sent to the Safety Board's laboratory in Washington, DC, for readout and evaluation. The CVR was played back normally and without difficulty and contained six separate channels of good quality $^{26}$ audio information. The recording started at 1712:58.2 and continued uninterrupted until 1914:01.3. A transcript was prepared of the entire 2-hour, 44.7-second recording (see appendix B).

1.11.2 Flight Data Recorder

The accident airplane was equipped with a Honeywell model solid state FDR, S/N 10452, that recorded airplane flight information (including altitude, airspeed, heading, wind direction and speed, control wheel and column position, elevator/aileron/rudder position, engine fan speed, thrust reverser status and position, thrust reverser interlock, brake pressure, and autobrake status) in a digital format using solid-state memory devices. The FDR showed no evidence of damage or excessive wear and was sent to the Safety Board's laboratory for readout and evaluation. The following information was obtained from the accident airplane's FDR data and physical evidence:

· The main landing gear touched down about 1,250 feet beyond the runway's approach threshold.$^{27}$ At the time, the airplane's ground speed was about 131 knots, its airspeed was 124 knots, its heading was 316°, and its vertical acceleration reached about 1.4 Gs.

Factual Information

AIRCRAFT Accident Report

· The ground spoilers were fully deployed, autobrakes were applied, and vertical acceleration increased to a peak value of about 1.7 Gs within about 1.2 seconds of touchdown.

· About 10 seconds after touchdown, engine fan speed ($N_1$) decreased from about 32 percent at touchdown to about 20 percent, where it remained for about 8 seconds.

· Autobrakes were deactivated about 12 seconds after touchdown, and pilot-comhanded brake pressure increased to 3,000 pounds per square inch (psi).

· The first indication of thrust reverser activity was recorded about 15 seconds after touchdown, with full deployment about 18 seconds after touchdown. N₁ reached 80 percent about 9 seconds later (about 27 seconds after touchdown) at a ground speed of about 62 knots.

· The thrust reversers were fully deployed and the brake pressure was 3,000 psi when the nose landing gear departed the runway overrun at a speed of about 53 knots.

● The airplane came to a stop about 500 feet beyond the end of the runway on a heading of about 340° with a collapsed nose landing gear about 8 seconds after it departed the runway overrun.

1.11.3 Flight Data Recorder Information From Other Landing Airplanes

FDRs from five air carrier airplanes that landed in the 25 minutes before the accident were evaluated. Table 2 provides a comparison of selected parametric data for those five air carrier airplanes and the accident flight.

Table 2. Comparison of selected parametric data for five air carrier airplanes and the accident flight.

*Note: The autobrake system initially applied the brakes for United Airlines flight 1446 and the accident flight.

**N/A in this table indicates not available.

Factual Information

AIRCRAFT Accident Report

1.12 Wreckage and Impact Information

The airplane came to rest on a magnetic heading of about 340° at the south side of an intersection located on the northwest corner of MDW. The airplane was resting on the engines, both main landing gear, and the nose of the fuselage, with the nose landing gear collapsed and folded aft. The damage to the airplane was largely limited to the forward lower fuselage, engine cowlings and components, forward portions of the wings, and other wing components,$^{28}$ with limited damage farther aft. The rear part of an automobile was found damaged beneath the forward portion of the airplane's left fuselage. Postaccident interviews and physical evidence indicate that the automobile was northbound on the roadway and was struck from behind by the airplane.

Postaccident examination and testing of components in the airplane's throttle, antiskid,$^{29}$ ground spoiler, and wheel brake systems revealed no evidence of preimpact anomalies. In addition, investigators examined the engine controls and the throttle quadrant (including the thrust levers) in the flight deck area and associated linkages below the cockpit floor level; no evidence of preimpact anomalies was found.

1.13 Medical and Pathological Information

In accordance with Federal regulations, postaccident drug testing was conducted on urine specimens obtained from the captain and first officer;$^{30}$ test results were negative. In addition, both pilots volunteered blood samples for analysis within 24 hours of the accident. These test results were negative for alcohol and a wide range of drugs, including drugs of abuse.$^{31}$

The Cook County Medical Examiner's Office reported the cause of death of the automobile passenger as "compressional asphyxia." Other postaccident medical information indicated that another automobile occupant received serious injuries, including multiple fractures, head injuries, and right shoulder pain, and 21 people (1 flight attendant, 17 airplane passengers, and 3 automobile occupants/pedestrians) received minor injuries, including multiple aches and pains, sprains/strains, contusions and abrasions, and a whiplash-type injury, as a result of the accident.

Factual Information

AIRCRAFT Accident Report

1.14 Fire

No evidence of an in-flight or a postcrash fire was found.

1.15 Survival Aspects

According to postaccident interviews and airport documentation, the first ARFF units arrived at the airplane about 2 minutes after the accident and assisted with the evacuation. The captain instructed a flight attendant to open the left front door and told the first officer to help passengers at the bottom of that door's evacuation slide.$^{32}$ He used a megaphone to advise passengers that they should evacuate through the front of the airplane. According to City of Chicago records, about 14 minutes after the accident, ARFF personnel positioned mobile stairs at the right rear door and assisted passengers in exiting through that door as well.

The first officer and about half of the airplane passengers evacuated through the left front cabin door. The captain, three flight attendants, and about half of the passengers evacuated through the right rear door using the mobile stairs provided by ARFF personnel. During postaccident interviews, flight attendants described the evacuation as “orderly” and stated that passengers deplaned calmly. The right front, left rear, and right and left overwing exits were not opened during the evacuation.

1.16 Tests and Research

1.16.1 Airplane Simulation and Performance Studies

A postaccident engineering study was conducted to examine the deceleration times and distances required for the accident flight and the four other SWA 737-700 airplanes that landed before it. The Safety Board's airplane performance study identified an airplane braking ability (braking coefficient)$^{33}$ that would replicate the accident airplane's ground speed and runway deceleration performance and quantified the effects that different winds, ground spoiler deployment schedules, and reverse thrust throttle settings and stowage schedules would have had on the airplane's stopping performance.

Factual Information

AIRCRAFTAccident Report

Simulations that replicated the accident airplane configuration, use of deceleration devices, and weather$^{34}$ and runway conditions (see case #31 in table 3) showed that, under these conditions, the airplane would have required about another 753 feet beyond the end of the runway to come to a stop. A simulation case performed under the same conditions but with an equivalent headwind instead of tailwind component (see case #33 in table 3) showed that the airplane could have stopped about 584 feet before the departure end of the runway. A simulation case performed under identical airplane configuration, weather, and runway conditions, but using SWA routine/planned deceleration procedures to decelerate,$^{35}$ showed that the airplane would likely have stopped about 1,351 feet beyond the end of the runway (see case #53 in table 3). Under the same conditions and if the pilots had used Boeing's reverse thrust procedures$^{36}$ (see case #54 in table 3), simulations showed that the airplane would likely have stopped about 531 feet beyond the end of the runway. However, simulations in which maximum reverse thrust was selected 2 seconds after touchdown and maintained until the airplane came to a complete stop (see case #60 in table 3) showed that the airplane could have stopped about 271 feet before the departure end of the runway.

Table 3. Stopping distances and runway exit speeds for various deceleration scenarios calculated during postaccident airplane performance simulations.

The previous four SWA 737-700 airplanes landed on runway 31C about 1853, 1901, 1902, and 1904; one of these airplanes exited the runway at taxiway B (the last taxiway before the runway end), the other three airplanes exited at the runway-end taxiway. FDR data indicated that the flight crews on these four airplanes deployed reverse thrust (three out of the four flight crews commanded maximum reverse thrust) early in the landing roll. The Safety Board's study showed that timely and sustained application of reverse

Factual Information

AIRCRAFT Accident Report

thrust (including maximum reverse thrust as needed)$^{37}$ could have been used to stop the accident airplane on the runway.

The study showed that the accident airplane landed in generally deteriorating runway surface conditions; the flight's braking ability was about five times worse than would be expected on a bare and dry runway. The study also stated that the calculated ground roll distances were most sensitive to the airplane braking coefficient magnitude, winds, and time delay to commanded reverse thrust under the landing conditions. However, the study noted that the landing distances would have been less sensitive to similar wind and time delay variations if the landings were conducted on a dry or wet runway.

1.17 Organizational and Management Information

1.17.1 Southwest Airlines Information

SWA began service on June 18, 1971, and is based in Dallas, Texas. At the time of the accident, SWA operated about 3,000 scheduled daily domestic departures to 62 destinations and had more than 31,000 employees. The company's all-737 fleet consisted of 194 737-300s, 25 737-500s, and 222 737-700s.

Five other runway-related accidents or incidents involving SWA have occurred since 1983,$^{38}$ including three lateral runway excursions and two runway overruns, one of which involved a contaminated runway surface (heavy rain).

1.17.2 Southwest Operations Guidance Information

1.17.2.1 Thrust Reverser Procedures and Information

SWA policies and procedures specified the use of thrust reversers for all landings, regardless of runway length or condition. At the time of the accident, SWA's FAA-approved flight operations manual (FOM) stated, in part, that after the airplane touches down on the runway, the pilots should do the following:

Initiate reverse thrust: Raise the reverse thrust levers to the reverse idle interlocks. After the interlocks release, modulate reverse thrust, as required. Avoid exceeding engine limits. Minimum reverse thrust is 65 percent N₁ [engine fan speed]. When required, reverse thrust to engine limits may be used. Initiating reverse thrust at touchdown is an important factor in

Factual Information

AIRCRAFT Accident Report

minimizing brake temperatures, minimizing brake and tire wear, and reducing stopping distances.

The SWA FOM also stated the following:

Under braking advisories less than 'GOOD' use Normal Landing Procedures except for the following:

[Manual] Brakes and thrust reversers should be applied together.[39]

Use thrust reversers as soon as possible during landing roll.

In addition, the SWA FOM stated the following:

Both pilots will monitor systems for warning flags, lights, or out of tolerance conditions.

The [first officer] will advise the captain of deviations from established policies, procedures, and/or regulations.

SWA pilots are trained to move the thrust reverser levers aft smoothly and promptly after touchdown and to keep their forearms on the throttle knobs to keep the throttles at idle during thrust reverser deployment. If the throttle levers are forward of the idle detent by about 1/4 inch,$^{40}$ the reverse thrust levers cannot be operated. A postaccident survey of SWA personnel and pilots, a review of SWA maintenance records, and a review of aviation safety reporting system (ASRS) data revealed no evidence of systemic thrust reverser difficulties. Several SWA pilots did report difficulties deploying the thrust reversers when they tried to move the reverse thrust levers past the interlock position too rapidly; those pilots reported that the levers moved readily when they tried to deploy the thrust reversers again after the interlocks released. Postaccident interviews with the previous 10 flight crews for the accident airplane revealed that they reported no difficulty deploying the thrust reversers.

According to SWA personnel, there was no policy allowing pilots to apply a credit for the use of reverse thrust during their landing distance assessments (which would increase the calculated stopping margin for a landing) until 1998, when a reverse thrust credit was incorporated into landing distance calculations for the 737-700 model only. SWA pilots received instruction regarding the reverse thrust credit during differences training when qualifying for the 737-700 model. However, until 1 week before the accident, the information in two out of three FOM locations incorrectly indicated that reverse thrust was not included in 737-700 OPC landing distance calculations. At the time of the accident, the information was correct in two of the three FOM locations. Most SWA

Factual Information

AIRCRAFT Accident Report

pilots interviewed after the accident were aware of the OPC reverse thrust credit for the 737-700; however, some were not.

1.17.2.2 Autobrake Procedures and Information

At the time of the accident, SWA planned to implement a policy requiring the use of autobrakes under certain landing conditions on December 12, 2005 (4 days after the accident). Previously, SWA's policy did not permit the use of autobrakes because the company's fleet was not then fully equipped with autobrakes. As the fleet became fully equipped, the company took steps to implement autobrake use. In preparation, SWA provided its pilots with a self-study training module on the autobrake system and related SWA procedures (which both accident pilots had completed). SWA pilots were also provided with a series of bulletins regarding the repeatedly delayed start-date for autobrake usage. The most recent of these bulletins was issued December 8, 2005, and noted that the company's autobrake procedures and policies were to be used by SWA pilots beginning December 12, 2005, and therefore were not in effect (or authorized) on the day of the accident.$^{41}$

During postaccident interviews, the pilots told Safety Board investigators that they had read the daily read-before-flight (RBF) letters before the accident flight but that they failed to notice the new delay in autobrake procedure implementation.$^{42}$ CVR evidence and postaccident statements indicated that they both believed that the autobrake policy was in effect for the accident flight. A previous autobrake-related RBF letter indicated that the autobrake policy would be in effect as soon as materials were available in the cockpit. On the day of the accident, “flow” cards and checklists with information regarding autobrake procedures had been placed in SWA airplanes.

When using autobrakes, pilots can select from several autobrake system settings, including the following:

· Maximum (MAX): Should be used when minimum stopping distance is required.$^{43}$

· Medium (MED): Should be used for wet or slippery runways or when landing rollout distance is limited.

· Minimum (MIN): These settings provide a moderate deceleration effect suitable for all routine operations.

1.17.2.3 On Board Performance Computer-Related Guidance and Information

Pilots may use a variety of aids when performing airplane performance and landing distance calculations. Options include tabular performance charts and on board electronic

Factual Information

AIRCRAFTAccident Report

computing devices (also known as OPCs at SWA). The FAA evaluates and approves operators' procedures for the use of electronic computing devices with an interactive interface, and advisory guidance regarding the certification and operational approval process for these devices is provided in AC 120-76A.$^{44}$ AC 120-76A addresses human factors design issues and contains references to other sources for detailed human factors guidance, including a series of reports developed by the Department of Transportation (DOT) in conjunction with the FAA regarding human factors in the design and evaluation of OPC-type devices.$^{45}$ The advisory material states that the results of calculations should be displayed in a manner that is understood easily and accurately and that users should be aware of any assumptions upon which the flight performance calculations are based.

Tabular charts preceded on board electronic computing devices and are still used by many airlines today. These charts present critical information and assumptions through notations directly on the applicable chart or on an introductory performance page. To calculate landing distance using a chart, pilots survey rows and columns of values, select the most appropriate value for conditions, and adjust for inputs accordingly. Use of charts sometimes requires mathematical adjustments or interpolations to account for values that are not exactly listed. OPC-like devices help reduce the pilots' workload by eliminating the need for pilot adjustments and interpolations; however, research shows that it is important for pilots to be aware of the critical underlying performance calculation assumptions.$^{46}$

As previously stated, SWA provides its pilots with an OPC, and the company's FOM provides guidance regarding the use of that OPC. The SWA FOM identifies, in part, the following runway conditions with regard to OPC use:

WET-FAIR – to be used when braking action is reported as fair; and

WET-POOR- to be used when braking action is reported as poor.

The SWA FOM further states the following:

The [OPC-calculated] landing distance information is provided to give an indication of the braking effort necessary to stop the airplane within the available landing length....Individual pilot braking technique and

Factual Information

AIRCRAFTAccident Report

experience will provide equivalent braking efforts that can then be related to the OPC output. The MAX distance is based on maximum manual braking (without the use of thrust reversers) at touchdown.

The approximate stop margins calculated by the OPC are based on three different levels of deceleration as defined by the autobrake system and are based on touching down 1,500 feet from the [runway approach] threshold. The MIN, MED, and MAX values are calculated using the deceleration rates for [associated autobrake settings]. The stop margins include the effects of reverse thrust (-300/-500: stop margins do not include the effects of reverse thrust).[47]

Additionally, according to SWA's FOM, company procedures authorize pilots to land using a MAX autobrake setting, “provided a positive stopping margin is computed” by the OPC.

Specific OPC-related training was provided to SWA pilots during 1 day of dispatch training and two additional classroom training periods. During training, one scenario addressed use of the OPC from takeoff to landing during a normal flight, whereas another addressed use of the OPC from takeoff to landing during an abnormal flight.$^{48}$ Additionally, upon completion of the specific OPC training, pilots spent 3 classroom days with a check airman instructor who covered additional FOM topics, including use of the OPC.

Most SWA pilots, instructors, and check airmen who were interviewed told investigators that the company's pilots had adapted well to the use of the OPC and had a good understanding of and trusted the system. There were no procedures in place for pilots to verify or check the numbers calculated by the OPC with another independent source.

Postaccident examination of the data stored on the accident OPC confirmed that the pilots had entered the expected airplane touchdown weight and updated weather data. As previously noted, evidence indicated that the pilots selected WET-FAIR and WET-POOR as possible runway conditions and that the OPC estimated 560 and 40 feet, respectively, of runway remaining under those conditions. (As previously noted, SWA procedures permit company pilots to land with any positive calculated stopping margin.) Based on its assumptions, the OPC display would reflect the landing distance associated with a maximum tailwind component of 5 knots for poor braking action even if the

Factual Information

AIRCRAFT Accident Report

computed tailwind component exceeded 5 knots. Figures 4 and 5 show OPC- displayed results of OPC calculations based on the accident conditions with fair and poor braking action, respectively. Note that in both figures the OPC display shows the tailwind value of 8 knots even though the displayed landing distance is based on the OPC tailwind limit of 5 knots. In figure 5, the white “8T” with a red background and the “Wind limits: 5T/10X” remark in white with a black background near the bottom of the display indicate that the tailwind limits for poor braking action were exceeded.

![WET FAIRRunway Condition:Airport IdentifierMDWKMDWAir Conditioning:Elev./Pressure Altitude620/BLEEDS ON482 FTMaximum OAT:Anti-lce:ENGINE ON53℃/128"FWind:090/11 MAGN-KTSLanding WeightLB119.7Temp/DP:3/5°C (27/23°F)Landing Flaps40Altimeter:30.07 In HgOuick Tumn:1512L8App ClbCk Wing Frost if Fuel Temp<+CVRef125Approx Stop MarginRwyLengthWindsMin2MedV AppMax tM)31C5826-DT8T/ 7X-810]35056014515 MMS1555MMS1751MMS1950MMS:Co-Arour91.3MEL/CDLModule MenuReturn\n](5/c30bHCsB7t5ziiaOum9G8B/pdf_78ab0cf185284213efdf3845e35acd1e_d32fefc5ba1ef1167290b72f43a949027490560193474857/tmp_zip_img/7e07cb80-84f3-45c0-a1a6-d1a55618e883.png)

Figure 4. OPC display showing the results of OPC calculations based on the accident conditions with fair braking action.

The Safety Board's investigation revealed that if SWA OPCs had used the actual tailwind component of 8 knots instead of the company limit of 5 knots, the stopping margin for poor braking action would have been -260 feet. Because of its negative value, this number would have been presented as bracketed white digits inside of a red block (instead of the standard black digits against white background) to alert the pilots that they could not safely land on the runway. The Board notes that calculations performed using Boeing's more conservative data, an 8-knot tailwind component, and poor braking action indicated that the airplane would have stopped 2,070 feet beyond the end of the runway. Similar calculations performed using fair braking action indicated that the airplane would have stopped 260 feet beyond the end of the runway. A review of SWA guidance and

Factual Information

AIRCRAFT Accident Report

training regarding OPC assumptions revealed one reference in the OPC section of the flight reference manual (FRM) but none in the FOM. Further, no references were made to this topic during initial, recurrent, or OPC-related ground training.

![Runway Condition:WET POORMDW KMDWAirport Identifier:482 FTAir ConditioningBLEEDS ONElev./Pressure Altitude620/128°FAnti-lce:ENGINE ONMaximum OAT:53/Wind090/11 MAGN-KTS119.7LBLanding WeightTemp/DP:-3/5°C [27/Z3°F)40Landing Flaps:Altimeter:30.07 In HgQulck Turn:151.2LBApp ClbCk Wing Frost if Fuel Temp<+DVRef125Approx Stop MarginMax (MVApp:RwryLengthWindsMin(2)Med(3)31C5826-DT8T7X[-730]-304014515° MMS155SMMS:175 MMS195O MMS:Go-Around:91.3Wind limits:5T/10XMEL/CDLReturnModule Menu\n Note: the white “8T” with a red background and the “Wind limits: 5T/10X” remark in white with a black background near the bottom of the display indicate that the tailwind limits for poor braking action were exceeded.

Figure 5. OPC display showing the results of OPC calculations based on the accident conditions with poor braking action.

As a result of its investigation of the July 31, 1997, accident involving a Federal Express McDonnell Douglas MD-11 that crashed while landing on runway 22R at Newark International Airport, Newark, New Jersey,$^{49}$ the Safety Board determined that some flight crewmembers may lack proficiency in the operation of airplane performance computing devices and that confusion about calculated landing distances may result in potentially hazardous miscalculations of available runway distances after touchdown. In August 2000, the Safety Board issued Safety Recommendation A-00-95, which asked the FAA to require principal operations inspectors (POI) assigned to Part 121 operators that

Factual Information

AIRCRAFT Accident Report

use auxiliary performance computers $^{50}$ to review and ensure the adequacy of training and procedures regarding the use of this equipment and interpretation of the data generated, including landing distance data.

As a result of this recommendation, in August 2002, the FAA issued Flight Standards Information Bulletin for Air Transportation 02-03, which was intended to 1) call attention to the importance of operating procedures and pilot training related to OPCs and 2) cause operators and POIs to review those procedures and related training to ensure their adequacy, if OPCs are to be used by the operator. In December 2002, Safety Recommendation A-00-95 was classified “Closed-Acceptable Action.”

1.17.2.4 Mixed Braking Action Report and Tailwind Limitation Guidance

SWA guidance indicates that mixed braking action reports are not unexpected during routine operations and company policy requires pilots to defer to the more critical braking action assessment when mixed braking action conditions are reported. Specifically, SWA's FAA-approved FOM, chapter 3, "Normal Operations," pages 3.23.1 through 3.23.5, states the following:

Braking action reports less than good are classified according to the most critical term [emphasis added] (fair, poor, nil, or combinations). Operations are prohibited on all surfaces classified as nil.

The Safety Board's review of SWA training materials revealed that, at the time of the accident, the topic of mixed conditions was not routinely or explicitly introduced to pilots during training. Further, the topic was not addressed in the FOM sections regarding braking action and runway friction reports, entering runway conditions into the OPC, and/or programming the OPC for landing. After the accident, SWA published a revision to chapter 3 of the FOM, which added, "If a combination is given (e.g., fair to poor), use the more restrictive of the two." In addition, SWA implemented pilot training specific to interpretation of braking action reports, including mixed conditions.$^{51}$

According to SWA's FOM, chapter 2 ("Operational Considerations"), page 2.2.6 "landing is not authorized ... when wind limitations are exceeded." The FOM, chapter 2, page 2.2.9, indicates that SWA's maximum tailwind component for landing under poor braking action conditions is 5 knots; under all other conditions, the maximum tailwind component for landing is 10 knots. As previously noted, when the wind limits for a given braking action are exceeded, the OPC displays a description of the limits on the bottom of the screen in white letters with black background, but uses SWA's programmed maximum tailwind component (not the actual computed component) to calculate landing distance. For an example, see the OPC display in figure 5 ("Wind limits: 5T/10X").

Factual Information

AIRCRAFTAccident Report

1.17.3 Southwest Airlines Postaccident Actions

As a result of this accident, SWA revised its operational policies and procedures and guidance as follows:

● Amended sections of its FOM to reinforce the company's policy requiring pilots to enter the most restrictive braking action report in the OPC for landing distance assessments and provided additional training specific to braking action reports, including mixed conditions.$^{52}$

● Revised its OPC to standardize the use of thrust reverser credit in landing distance assessments for all airplane types and to modify the landing output screens to show the amount of reverse thrust needed to obtain the calculated distances.

● Reinforced thrust reverser policies regarding the immediate deployment of thrust reversers after landing.

● Revised the procedures for use of thrust reverse to be consistent with the Boeing guidance, such that pilots are to begin reducing the reverse thrust at 60 knots instead of 80 knots.

● Clarified FOM guidance regarding the responsibility of the monitoring pilot to monitor thrust reverser deployment and to call out any specific related deviation.

● Implemented an autobrake familiarization period before autobrake use (in addition to the existing flight crew autobrake training and related information package) and revised FOM to include a technical description of the autobrake system. SWA required that pilots complete at least four familiarization landings (two as the flying pilot and two as the monitoring pilot) on dry runways with ample stopping margins before using the autobrake system on a routine basis.

● Added a 15 percent safety margin to its arrival landing distance calculations and revised its OPC to reflect the additional margin.$^{53}$

1.18 Additional Information

1.18.1 Airplane Landing Performance Information

Two categories of airplane landing distance performance information are pertinent to normal commercial airplane operations. The first, preflight (or dispatch) landing distance

Factual Information

AIRCRAFTAccident Report

performance data, is used during flight planning to determine the maximum takeoff weight at which the airplane can depart an airport and, after its planned fuel burn, land on the available landing distance at the destination/alternate airport. This determination is based on specific 14 CFR requirements for dry or wet/slippery runway conditions. Dispatch landing distance calculations are intended to ensure that dispatched airplanes will be able to land safely at the intended destination airport or a planned alternate and are based on estimated landing weights and forecast conditions. According to Federal regulations, the dry and wet/slippery landing performance data used for dispatch calculations are obtained by multiplying the numbers $demonstrated^{54}$ during certification landings on a level, smooth, dry, hard-surfaced runway by factors of 1.67 and 1.92, respectively.$^{55}$

The second category, arrival (or operational) landing distance information, is used by pilots while en route and uses updated information, including runway conditions, weather, and planned configurations, to determine the landing distance required. Airplane landing performance data for conditions other than bare and dry are typically calculated rather than demonstrated via a flight test. Operational landing distance assessments are intended to ensure that the arrival weather and runway surface conditions and the planned airplane configuration, pilot technique, and deceleration devices will result in a safe landing distance at the arrival weight.

Dispatch planning distance calculations are required and standardized by U.S. and international aviation authorities. However, U.S. Federal regulations do not require or standardize arrival landing distance assessments, nor do they specify safety margins for such assessments.

1.18.1.1 Previously Issued Urgent Safety Recommendation Related to Landing Distance Assessments

As a result of this accident, on January 27, 2006, the Safety Board issued urgent Safety Recommendation A-06-16, which asked the FAA to do the following:

Immediately prohibit all 14 CFR Part 121 operators from using the reverse thrust credit in landing performance calculations.

The stated intent of this recommendation was to ensure adequate landing safety margins for landings on contaminated runways. The FAA responded in part by conducting an internal review of existing regulations, orders, notices, ACs, International Civil Aviation Organization (ICAO) and foreign country requirements, airplane manufacturer-developed material, independent source material, and the current practices of air carrier operators.

Factual Information

AIRCRAFTAccident Report

The FAA does not require landing performance calculations at the time of arrival, nor does it impose standards for these manufacturer-supplied or operator-packaged landing performance data or the use of such data. Therefore, the FAA observed numerous inconsistencies and wide variation in operators' practices regarding airplane landing performance calculations at the time of arrival. These inconsistencies were observed in numerous related areas, including the circumstances under which the landing distance for the time of arrival was calculated; the data used for such calculations, which were either provided by the manufacturer or developed by the operator or a third-party vendor; the currency of landing distance assessment data; application of safety margins; the existence of landing distance performance information; and the application of credit for the use of thrust reversers. Landing distance performance information is available in a wide variety of informational documents and is available for a range of runway or braking action conditions using various airplane deceleration devices and settings under a variety of meteorological conditions, depending on the operator and the source.

During the Safety Board's investigation of the SWA flight 1248 accident, investigators determined that two different operators were using manufacturer-supplied landing performance data that were not the most suitable or currently available. Further, in some cases, the landing performance data presented by the operator and/ or third-party vendor were less conservative (provided a larger stopping margin) than the manufacturer's data for the same conditions (as was the case with SWA's data in this accident). The operational landing performance data used to define landing limitations may be based on a wide range of assumptions, depending on the manufacturer and whether the data have been modified before presentation to pilots. Although operators practices may differ, manufacturer-provided dispatch landing performance data are typically included in an airplane flight manual, while arrival landing performance data are included in the airplane's quick reference handbook for accessibility in the cockpit. (Both dispatch and arrival landing performance data are typically available to operators using electronic flight bags [EFB].)

On June 7, 2006, the FAA published an "Announcement of Policy for Landing Performance After Departure for All Turbojet Operators," which stated, in part, that the FAA considered a 15 percent margin as the minimum acceptable safety margin between the expected actual airplane landing distance and the available runway landing distance at the time of arrival. In a June 13, 2006, letter to the Safety Board, the FAA stated its belief that the actions described in its June 7 notice would yield a greater safety benefit than a blanket prohibition against taking credit for use of thrust reversers. The Board supported the FAA's planned action and its timely implementation. As a result, the FAA planned to issue mandatory Operations Specification (OpSpec) N 8400.C082 to all 14 CFR Part 91 subpart K, 121, 125, and 135 turbojet operators, requiring the following:

● Use of an operationally representative air distance;

● Use of data at least as conservative as the manufacturer's data;

Factual Information

AIRCRAFT Accident Report

· Use of the worst reported braking action for the runway during landing distance assessments; and

· Operators' addition of an extra margin of at least 15 percent to the landing distance calculation.$^{56}$

Further, OpSpec N 8400.C082 would require POIs to ensure that operators' flight crew and dispatcher training programs provide information about all aspects and assumptions of actual landing distance performance determinations.

The FAA intended that operators comply with OpSpec N 8400.C082 by October 2006. However, the FAA encountered considerable industry opposition to its June 7 proposal, and, on August 31, 2006, decided not to issue the mandatory OpSpec but, rather, to pursue formal rulemaking regarding these issues. In the interim, the FAA published Safety Alert for Operators (SAFO) 06012, compliance with which was voluntary. SAFO 06012 suggested that operators (1) establish procedures that require assessing the landing distance as close as practicable to the time of arrival if conditions have adversely changed since the preflight landing distance assessments, (2) apply a safety margin of at least 15 percent to the calculated airplane landing distance when such assessments are required at the time of arrival, and (3) provide information regarding all aspects of actual landing distance performance assessments in their flight crew and dispatcher training programs, among others. FAA personnel told Safety Board staff that the FAA intended to pursue formal rulemaking in the area of landing distance assessments and believed that operators would voluntarily comply with SAFO 06012 in the interim.

The Safety Board is currently investigating two additional accidents involving contaminated runway overruns by air carrier airplanes. On February 18, 2007, a Shuttle America Embraer EMB-170 ran off the end of snow-contaminated runway 28 at Cleveland Hopkins International Airport in Cleveland, Ohio. This ongoing investigation has revealed that Shuttle America did not require its pilots to perform landing distance assessments based on conditions at the time of arrival.$^{57}$ Additionally, on April 12, 2007, a Pinnacle Airlines Bombardier Regional Jet CL600-2B19 ran off the end of snow-covered runway 28 at Cherry Capital Airport in Traverse City, Michigan. This ongoing investigation has revealed that Pinnacle had incorporated an arrival landing distance assessment

Factual Information

AIRCRAFT Accident Report

requirement consistent with SAFO 06012;$^{58}$ however, the accident flight crew in this case did not perform an arrival landing distance assessment.$^{59}$

In a May 8, 2007, response regarding Safety Recommendation A-06-16, the Safety Board stated, “A year after this urgent recommendation was issued, the FAA has not yet taken any effective action in response to it.” The Board cited FAA-issued guidance advising the use of a 15 percent safety factor in landing distance assessments but noted that the FAA was unable to say how many Part 121 operators had adopted that guidance. In its letter, the Board classified Safety Recommendation A-06-16, “Open–Unacceptable Response.”

1.18.1.2 Landing Distance Assessment Technical Bulletin

In January 2007, Safety Board staff attended a meeting with FAA, Boeing, SWA, and SWA Pilots Association (SWAPA) personnel at which the history and practices related to landing distance assessments at the time of arrival were discussed. Figure 6 shows a related draft winter operations guide that was developed by an industry group.

SWA is currently incorporating the information contained in this guide, which it plans to incorporate in October 2007, and Boeing attached similar guidance to a bulletin, dated August 23, 2007, that was issued to all operators of Boeing turbojet airplanes.$^{60}$ The Boeing guidance recommends that operators develop arrival landing distance assessment procedures for their flight crews to use to ensure that a full-stop landing can be made on the arrival runway in the conditions (weather and runway) existing at the time of arrival and with the deceleration means and airplane configuration to be used. The Boeing guidance also recommends that the landing distance assessment use the most adverse braking condition in the landing distance assessment and that an additional safety margin be applied to the resultant landing distance.

Factual Information

AIRCRAFT Accident Report

BRAKING ACTION

PIRLPS

When braking action conditions less than Good are encountered, pilots are expected to provide a PIREP based on the definitions provided in the table below. Until FAA guidance materials are revised to replace the term Fair with Medium, these two terms may be used interchangeably. The terms "Good to Medium" and "Medium to Poor" represent an intermediate level of braking action, not a braking action that varies along the runway length. If braking action varies along the runway length, such as the first half of the runway is Medium and the second half is Poor, clearly report that in the PIREP (e.g., "First half Medium, last half Poor").

Correlating Expected Runway Conditions:

The correlation between different sources of runway conditions (e.g., PIREPs, runway surface conditions and MU values) are estimates. Under extremely cold temperatures or for runways that have been chemically treated, the braking capabilities may be better than the runway surface conditions estimated below. When multiple sources are provided (e.g., braking action medium, runway covered with ice and runway MU is 27/30/28) conflicts are possible. If such conflicts occur, consider all factors including data currency and the type of airplane a PIREP was given from. A valid PIREP or runway surface condition report are more reliable indicators of what to expect than reported runway MU values.

Runway Friction MU Reports

MU values in the U.S. are typically shown as whole numbers (40) and are equivalent to the ICAO standard decimal values (40). Zero is the lowest friction and 100 is the highest MU friction. When the MU values for any one-third zone of an active runway is 40 or less, a report should be given to ATC by airport management for dissemination to pilots. The report will identify the runway, the time of measurement, the type of friction measuring device used, MU values for each zone and the contaminant conditions (e.g., well snow, dry snow, slush, deicing chemicals). While the table below includes information published by ICAO correlating runway friction measurements to estimated braking actions, the FAA cautions that no relable correlation exists. Runway MU values can vary significantly for the same contaminant condition due to measuring techniques, equipment calibration, the effects of contamination on the friction measuring device and the time passage since the measurement. Do not base landing distance assessments solely on runway MU friction reports. If MU is the only information provided, attempt to ascertain the depth and type of runway contaminants to make a better assessment of actual conditions.

BRAKING ACTION

Note: The KAO term Unrelliable and SNOTAM code of "9" indicates commission is outside the approved operational range for the fraction, measuring equipment in use and therefore Mu values are not provided. This typically occurs in Poor or worse conditions (greater than 1/3" of met, major, check or standing water) whereby a potential for hydroplaning should be expected. Use PIREP and the depth and type of visors, costness to anzez actual braking condition.

This page is advisory information as developed by a team of US airline technical pilots and other interested parties. The creation of the table was initiated by a FAA workshop on runway condition reporting in held in August of 2006.

Figure 6. Draft winter operations guide that was developed by an industry group.

Factual Information

AIRCRAFT Accident Report

1.18.2 Contaminated Runway and Landing Information

1.18.2.1 Runway Surface Condition Reports

Three methods typically used to describe a runway's surface condition are: 1) runway contaminant type and depth observations, 2) ground surface vehicle friction measurements,$^{61}$ and 3) pilot braking action reports. Safety Board public hearing testimony indicated that, regardless of the method used, the reported runway surface conditions may differ from the actual runway surface conditions encountered by a landing flight.

In SAFO 06012, the FAA stated that joint industry and international government tests have not established a reliable correlation between any of these runway surface condition description methods and an airplane's braking ability. In part, the FAA attributed this to the fact that runway surface conditions can change significantly in very short periods of time, depending on precipitation, accumulation, usage, temperature, direct sunlight, and runway maintenance/treatment. Runway contaminant type and depth reports may also be adversely affected by the observer's vantage point and/or a lack of uniformity of contaminants across the runway's surface. The FAA also stated that operators should not base their landing distance calculations solely on ground surface vehicle runway friction measurements because extensive testing did not indicate that "a repeatable correlation exists through the full spectrum of runway contaminant conditions."$^{62}$

Further, pilot braking action reports are subjective, reflecting individual pilot expectations, perceptions, and experiences, and are sensitive to airplane type and the actual deceleration methods used to slow or stop the airplane. Mixed pilot braking action reports (for example, fair for the first half of the runway and poor for the second half), and conflicting braking action reports from different sources (for example, an air carrier pilot, a general aviation pilot, or a ground vehicle) can also make the interpretation and use of such reports more difficult. The FAA acknowledges that braking action reports are subjective and advises pilots to consider all available information and make landing decisions based on the most restrictive reports, the pilots' experience, and sound judgment.

1.18.2.2 Correlation Between Runway Surface Condition and Airplane Braking Ability

During its investigation of this accident, the Safety Board noted that different methods and terminologies were used throughout the aviation industry to define the relationship between runway surface condition and an airplane's braking ability (also

Factual Information

AIRCRAFT Accident Report

termed “airplane braking coefficient” in this report). For example, the European Aviation Safety Agency (EASA) and Joint Aviation Authorities (JAA) state that a correlation between contaminant type and depth and the effective braking ability of an antiskid-controlled braked wheel “may be used to [calculate airplane landing performance conservatively] in the absence of any direct test evidence.” Both Boeing and SWA calculate operational airplane landing performance based on correlations between airplane braking ability and braking action reports.$^{63}$ Transport Canada provides guidance that can be used to correlate ground surface vehicle friction survey measurements to airplane performance on certain winter-contaminant surfaces in the form of Canadian Runway Friction Index (CRFI) tables in its Aeronautical Information Manual.$^{64}$

Existing FAA guidance on runway surface condition reporting, contained in AC 91-6A, “Water, Slush, and Snow on the Runway,” dated May 24, 1978, does not correlate runway braking action and an airplane’s braking ability. In August 1989, the FAA issued a draft AC (91-6B), “Performance Information for Operation with Water, Slush, Snow, or Ice on the Runway,” that proposed that such a correlation be used “if the braking performance is based on analysis rather than tests.” However, the draft AC was never published, and the guidance contained in AC 91-6A remains in effect.

The FAA allows airplane manufacturers and operators (like Boeing and SWA) to define custom braking action/airplane braking ability correlations. SAFO 06012 advocates the use of a specific correlation between reported braking action and runway contaminant type and depth to predict turbojet landing performance when manufacturer-supplied wet or contaminated runway landing distance data are unavailable. In addition, SAFO 06012 stated, “The FAA considers the data developed for showing compliance with the European contaminated runway certification...to be acceptable for making landing distance assessments for contaminated runways at the time of arrival.”

ICAO published yet another method used to define the relationship between runway surface condition and an airplane's estimated braking action. This correlation of the measured runway braking action (MU reading) to estimated braking action is shown in table 4.

Table 4. Correlation of the measured runway braking action to estimated braking action.

Factual Information

AIRCRAFT Accident Report

1.18.2.2.1 Canadian Runway Friction Index

A detailed method of measuring and reporting friction on contaminated runways to determine landing distances has been in use in Canada for about 30 years. Runway friction values obtained from decelerometers (DEC) are reported as CRFI values and are included in surface condition reports and notices to airmen. The information contained in the CRFI tables is based on field test performance data of airplanes braking on winter-contaminated surfaces and provides recommended landing distances based on the CRFI values. Figure 7 shows the CRFI values for various runway surface conditions, highlighting the CRFI values for loose snow 3 millimeters (mm) deep or less on pavement, which ranged from 0.16 to 0.76.

〔图〕插图

Figure 7. CRFI values for various runway surface conditions. Note that the CRFI values for loose snow 3 mm deep or less on pavement ranged from 0.16 to 0.76 (see the bold horizontal line).

1.18.2.2.2 International Runway Friction Index

In January 1996, the Joint Winter Runway Friction Measurement Program (JWRFMP), consisting of a group of representatives from international organizations,$^{65}$ convened to do the following:

· Study methods of friction measurement and define an International Runway Friction Index (IRFI) for worldwide use;

Factual Information

AIRCRAFTAccident Report

● Establish an international methodology whereby a common indication of runway conditions could be established worldwide; and

● Study the operational performance of aircraft on contaminated surfaces and establish a relationship with the harmonized IRFI.

In contrast to the CRFI, which used only DECs in measuring friction values, the IRFI was designed to use readings from a variety of friction testing devices (DEC and continuous friction measurement equipment [CFME] from multiple manufacturers). The results of this study were incorporated into American Society for Testing and Materials report 2100-02, "Standard Practice for Calculating the International Runway Friction Index," which prescribed methods for calculating the IRFI for winter surfaces and produced a harmonized scale for expressing pavement friction characteristics, regardless of the friction measurement equipment used. The IRFI obtained by using this practice has not been extended to address the braking performance of an aircraft; therefore, no tables of recommended landing distances based on the IRFI exist at this time.

Several FAA publications$^{66}$ indicate that the FAA does not believe that it is possible to predict aircraft braking performance from MU values obtained from runway friction surveys. Further, according to the FAA's Aeronautical Information Manual, “no correlation has been established between MU values and the descriptive terms ‘good,’ ‘fair,’ ‘poor,’ and ‘nil’ used in braking action reports.”

1.18.2.3 Previous Contaminated Runway-Related Safety Recommendations

In 1982, the Safety Board conducted a special investigation to examine commercial airplane operations on contaminated runways.$^{67}$ As a result of this investigation, the Board issued several contaminated runway-related safety recommendations to the FAA. Safety Recommendation A-82-152 asked that the FAA do the following:

Amend 14 CFR 139.31 and ... 139.33 to require that airports certified under 14 CFR Part 139 and located in areas subject to snow or freezing precipitation have an adequate snow removal plan, which includes criteria for closing, inspecting, and clearing contaminated runways following receipt of "poor" or "nil" braking action reports and to define the maximum snow or slush depth permissible for continued flight operations.

On November 18, 1987, the FAA issued Amendment 139-14 to Part 139, requiring snow and ice control plans in ACMs at airports where snow and icing conditions regularly occur. As a result of this action, the Safety Board classified Safety Recommendation A-82-152 “Closed – Acceptable Action.”

Factual Information

AIRCRAFT Accident Report

Safety Recommendation A-82-155 asked that the FAA do the following:

Convene an industry-government group to develop standardized criteria for pilot braking assessments and guidance for pilot braking action reports for incorporation into pilot training programs and operations manuals.

The FAA formed the Joint Aviation/Industry Landing and Takeoff Performance task group to review this recommendation, among others. The task group included representatives from Aerospace Industries Association, Air Line Pilots Association, Air Transport Association of America, Flight Safety Foundation, Inc., National Air Carrier Association, Inc., and the Regional Airline Association. However, because the FAA provided no evidence of progress in this area after 4 years, the Safety Board classified Safety Recommendation A-82-155 “Closed-Unacceptable Action.”

Safety Recommendation A-82-168 asked that the FAA do the following:

In coordination with the National Aeronautics and Space Administration [NASA], expand the current research program to evaluate runway friction measuring devices which correlate friction measurements with airplane stopping performance to examine the use of airplane systems such as antiskid brake and inertial navigation systems to calculate and display in the cockpit measurements of actual effective braking coefficients attained.

In a response letter dated April 1, 1983, the FAA indicated that it was working with NASA to form a runway braking action test program. In a January 1984 letter, the FAA indicated that it was involved with NASA in efforts to develop a method for obtaining runway braking condition information with a more quantitative basis than subjective pilot reports. However, in a May 5, 1987, letter, the FAA expressed concern that such a system would encourage operations from a runway with a very low friction coefficient and, further, that it would be of little value because of the differences in braking performance between dissimilar aircraft models.

In response, the Safety Board stated that it did not believe that the FAA and NASA had conducted sufficient research to conclude that objective measurements taken from dissimilar airplanes would not be meaningful and that “such reports would be very useful to airport operators as a means of detecting the degradation of runway conditions in winter weather and would provide a basis upon which the pilots of large airplanes could make better decisions.” Therefore, in April 1988, the Board classified Safety Recommendation A-82-168 “Closed–Unacceptable Action.”

As a result of the December 20, 1995, accident involving a Tower Air 747 at John F. Kennedy International Airport,$^{68}$ the Safety Board issued Safety Recommendation A-96-164, which asked that the FAA do the following:

Factual Information

AIRCRAFT Accident Report

Require the appropriate Aviation Rulemaking and Advisory Committee to establish runway friction measurements that are operationally meaningful to pilots and air carriers for their slippery runway operations (including a table correlating friction values measured by various types of industry equipment), and minimum coefficient of friction levels for specific airplane types below which airplane operations will be suspended.

In its response, the FAA stated that it did not consider it technologically feasible to establish runway friction measurements that were operationally meaningful to pilots and air carriers for slippery runway operations. The FAA noted its participation in the JWRFMP, which had a goal of developing the IRFI and correlating it with airplane stopping capability. However, the FAA maintained that there were serious shortcomings in several operationally significant aspects of the IRFI standard, in addition to the historical record of failures attempting to correlate ground friction measurements with airplane performance. The FAA did not expect any new developments related to this recommendation.

In June 2002, the Safety Board responded that, although the FAA's effort to develop an operationally meaningful runway friction measurement tool was unsuccessful, it did result in the development of an international standard for determining a runway friction index. The Board also stated that proposed testing might yield more meaningful tools and encouraged the FAA to continue its efforts in this area. However, the Board acknowledged that the technology to convert the runway friction index into an operational tool did not exist at the time and, therefore, classified Safety Recommendation A-96-164 "Closed—Reconsidered."

As a result of the June 1, 1999, accident involving an American Airlines MD-82 at Little Rock National Airport in Little Rock, Arkansas,$^{69}$ the Safety Board issued Safety Recommendation A-01-54, which asked that the FAA do the following:

For all 14 CFR Part 121 and 135 operators, require the use of automatic brakes, if available and operative, for landings during wet, slippery, or high crosswind conditions, and verify that these operators include this procedure in their flight manuals, checklists, and training programs.

On June 21, 2004, the FAA issued a notice (N8400.68) to its POIs, recommending the use of autobrakes for landings in adverse conditions caused by weather and directing POIs to convey the information in N8400.68 to their respective certificate holders. Because issuance of this notice met the intent of the recommendation, the Safety Board classified Safety Recommendation A-01-54 “Closed-Acceptable Alternate Action.” According to SWA representatives, the company’s efforts to equip its airplanes with autobrakes and develop and implement related procedures stemmed, in part, from these actions.

Factual Information

AIRCRAFTAccident Report

1.18.3 Previous Runway Safety Area Safety Recommendations

As a result of its investigation of the May 6, 2003, accident involving a Southwest Airlines airplane that overran the end of the runway after landing at Burbank, California,$^{70}$ the Safety Board issued Safety Recommendations A-03-11 and -12, which addressed RSAs and asked that the FAA do the following:

Require all 14 Code of Federal Regulations Part 139 certified airports to upgrade all runway safety areas that could, with feasible improvements, be made to meet the minimum standards established by Advisory Circular 150/5300-13. These upgrades should be made proactively, not only as part of other runway improvement projects. (A-03-11)

Require all 14 Code of Federal Regulations Part 139 certified airports to install engineered materials arresting systems in each runway safety area available for air carrier use that could not, with feasible improvements, be made to meet the minimum standards established by Advisory Circular 150/5300-13, "Airport Design." The systems should be installed proactively, not only as part of other runway improvement projects. (A-03-12)

In an August 7, 2003, letter, the FAA indicated that it agreed with the intent of these recommendations and stated that FAA Order 5200.8, "Runway Safety Area Program," established a program to bring all RSAs up to current standards, whenever possible. The letter stated that the FAA's goal was to upgrade 456 RSAs by 2007 and that such improvements "may be initiated at any time." The FAA stated that its goal was to upgrade at least 65 RSAs per year through 2007 and that 71, 68, and 74 RSAs were upgraded in fiscal years 2000, 2001, and 2002, respectively. The FAA also noted that eight EMAS beds had already been installed and that several more installations were planned. The Board asked the FAA to provide annual updates on RSAs that could not meet the standards and the specific alternatives that would be used to improve the safety of these RSAs.

The issue of RSA improvements was discussed at the Safety Board’s June 2006 public hearing that was held for the accident involving SWA flight 1248. In response to questioning during this hearing, FAA personnel indicated that, under current FAA policy, it is possible that some RSAs will not meet the dimensional standards or have arrester beds installed even after the FAA considers its improvement projects successfully completed. In a July 7, 2006, letter, the FAA indicated that 208 RSA upgrades and 15 EMAS installations had been completed though fiscal year 2005. The letter further stated that more than 90 percent of the RSA upgrades would be completed by 2010, and all RSA

Factual Information

AIRCRAFT Accident Report

upgrades would be completed by 2015. A recent update from FAA personnel indicated that 303 RSA improvement projects were completed. The update further indicated that 37 RSA upgrades and 5 EMAS installations were completed in fiscal year 2006 and that 20 RSA upgrades and 1 EMAS installation had been accomplished to date in fiscal year 2007. Safety Recommendations A-03-11 and -12 are currently classified "Open—Acceptable Response."

AIRCRAFTAccident Report

2. ANALYSIS

2.1 General

The pilots were properly certified and qualified under Federal regulations. No evidence indicated any medical or behavioral conditions that might have adversely affected their performance during the accident flight. There was no evidence of flight crew fatigue.

The accident airplane was properly certified and was equipped, maintained, and dispatched in accordance with industry practices.

No evidence indicated any failure of the airplane's powerplants, structures, or systems that would have affected the airplane's performance during the accident landing.$^{71}$

The pilots received thorough weather information for MDW and two alternate airport destinations in their dispatch documents and were well aware of the winter weather conditions in the area. They obtained numerous weather updates while en route from BWI to MDW and discussed conditions under which they would divert to one of the alternate destinations. Therefore, the Safety Board concludes that the pilots had adequate initial and updated weather information throughout the flight.

About 10 inches of snow accumulated at MDW on the day of the accident, and snow was falling at a moderate rate at the time of the accident. However, the accident runway had been recently cleared and treated with dece fluid, and four other SWA 737-700 airplanes landed and successfully stopped on runway 31C in the 21 minutes before the accident.$^{72}$ On the basis of this information, the Safety Board concludes that MDW personnel monitored runway conditions and provided appropriate snow removal services on the night of the accident.

This analysis will discuss the flight crew's decisions and actions, the clarity of assumptions used in OPCs, company policies and guidance, arrival landing distance assessments and safety margins, runway surface condition assessments and braking action reports, airplane-based friction measurements, and RSAs.

Analysis

AIRCRAFTAccident Report

2.2 Pilots' Decision to Land, Knowledge, and Actions

During its investigation, the Safety Board evaluated the pilots' decision to land at MDW and their actions during the approach and landing. Section 2.2.1 details the pilots' use of braking action reports, which included mixed braking actions, during their arrival landing distance assessments. Section 2.2.2 discusses the information displayed by the OPC during the arrival landing distance assessment and the pilots' awareness of the underlying OPC assumptions. Section 2.2.3 explains the pilots' use of autobrakes and reverse thrust during the accident landing. Integral to these issues is the pilots' awareness of SWA guidance and policies relevant to their decision and actions during the accident landing. These issues are addressed in this and subsequent sections.

2.2.1 Interpretation and Use of Mixed Braking Action Reports

As previously noted, the accident pilots were aware of the inclement weather in the Chicago area before they left BWI and obtained updated weather information throughout the flight. The Safety Board's review of recorded CVR information indicated that weather, landing performance assessments, landing criteria (including autobrake usage), and suitable alternates dominated the crew's conversation during the 2-hour flight.

Although not required by FAA regulations, SWA policies required the company's pilots to perform a landing distance calculation before the approach, using updated weather, airplane configuration,$^{73}$ and runway conditions. On the basis of the most current ATIS report for MDW, the accident pilots evaluated and discussed performance calculations for both fair and poor reported braking conditions. Although the pilots' calculations resulted in positive stopping margins for both fair and poor braking conditions (560 and 40 feet, respectively), and company policy indicated that landing was authorized with any positive stopping margin, the crew was concerned about the small positive stopping margin with poor braking action. Information from the CVR and postaccident interviews indicates that the pilots were also aware of a company policy for a maximum 5-knot tailwind component with a reported braking action of poor. Updated wind information resulted in a landing tailwind component of 8 knots. The pilots verbalized the decision not to land if the braking action was reported as poor for the full length of the runway.

As the airplane neared MDW, air traffic controllers provided the accident pilots with mixed runway 31C braking action reports. These reports indicated that the braking action was good or fair for the first half of runway 31C and poor for the second half. (The Safety Board notes that the accident flight was cleared for the approach to runway 31C because approach visibility requirements precluded approaches to all other MDW runways on the night of the accident.) However, the MDW controller did not routinely follow FAA procedures requiring controllers to include the type of airplane from which the braking action reports were made; in this case, the reports were provided by the pilots of several arriving 737s. Further, the controller did not provide the accident pilots with a report obtained from the pilot of a smaller airplane that described the braking action as

Analysis

AIRCRAFT Accident Report

poor, as required. Therefore, the Safety Board concludes that the MDW ATCT controller did not follow FAA guidance when he did not provide all of the required braking action report information.$^{74}$

All of the braking action reports provided by ATC to the accident pilots were mixed and reported poor braking action on some portion of the runway. For example, 8 to 9 minutes before touchdown, the pilots received a braking action report of “fair...except at the end it’s poor,” and 3 minutes before touchdown they received a braking action report of “good for the first half, poor for the second half.” SWA policy requires pilots to defer to the more critical braking action assessment when they receive mixed braking action reports. Therefore, because “poor” braking conditions were reported for a portion of the runway and SWA guidance indicates a maximum 5-knot tailwind to land if such conditions are reported, the pilots should not have landed at MDW. The Safety Board concludes that because the pilots did not use the more critical braking action term (poor) during their landing distance assessment (which, combined with the associated tailwind limitation, would have required them to divert), they were not in compliance with SWA’s policies.

The pilots did not discuss interpretation of mixed runway condition reports, although their behavior and other discussion suggests that they interpreted the runway condition as closer to fair than poor. They stated during postaccident interviews (and CVR evidence indicates) that they were not aware of SWA's guidance regarding mixed braking action reports. On the day of the accident, three preceding company aircraft (same make, model, policies, and procedures) landed with braking action reports containing the term poor and with similar wind conditions. Based on this and information obtained from postaccident interviews, it appears that other SWA pilots also were not aware of the mixed braking action report guidance in the FOM or did not adhere to it. The fact that other SWA pilots decided to land at MDW in these conditions likely influenced the accident pilots' decision to land; the accident pilots were less likely to consider their decision to land as contrary to company guidance if other SWA crews landed in similar conditions.

SWA guidance regarding how to provide a braking action report includes an example of a mixed condition report, indicating that mixed conditions were not unexpected during routine operations. However, the Safety Board's review of SWA training materials revealed that the topic of mixed conditions was not routinely introduced to pilots during training and was absent in the FOM for the topics of braking action and runway friction reports, entering runway condition into the OPC, and programming the OPC for landing, all of which defined the runway condition categories.

The Safety Board notes that, after this accident, SWA amended the wording in its FOM to clarify its policy regarding mixed braking action reports and provided its pilots with additional training specific to braking action reports, including mixed conditions.

Analysis

AIRCRAFT Accident Report

2.2.2 On Board Performance Computer Displays and Underlying Assumptions

The Safety Board evaluated the clarity of the information displayed to the pilots on the SWA OPC and the underlying assumptions (including reverse thrust credit) upon which the resultant landing distance assessments were based. Pilots use a variety of aids to accomplish airplane performance calculations, including tabular performance charts. The information on tabular charts is designed to be clear and readily available;$^{75}$ however, pilots must survey rows and columns and select the most appropriate value, apply required adjustments, and sometimes interpolate between listed values. SWA provides its pilots with an OPC for such calculations. Using an OPC or similar electronic computing device instead of tabular charts can decrease the pilots' workload because the computing device can automatically apply adjustments and interpolate based on the operator's programming. However, if pilots misunderstand the output because they are unaware of critical performance calculation assumptions, use of an electronic computing device can lead to errors in decision-making.

For example, as the accident pilots neared MDW, they used the OPC to calculate the airplane's landing distance multiple times, assessing updated weather conditions and stopping margins on runway 31C under both fair and poor braking action conditions. All of the resultant OPC calculations indicated that they could land and stop the airplane in the available runway length. The OPC indicated a stopping margin of about 560 feet before the end of the runway for fair braking action and about 40 feet before the end of the runway for poor braking action. However, evidence indicates that the landing distances displayed on the OPC could have been misleading to the crew because the pilots were not aware of at least two underlying OPC assumptions, neither of which was displayed on the OPC. Both of these assumptions resulted in OPC indications showing larger (more favorable) stopping margins.

One OPC assumption that the accident pilots were not aware of was that stopping margins displayed by the OPC for poor runway conditions were in some cases based on a lower tailwind component than that which was presented. Typically, the stopping margin output corresponded to the presented tailwind component. However, the tailwind component exceeded the 5-knot limit for poor runway conditions, but the displayed stopping margin was instead based on the tailwind limit of 5 knots, not the actual 8-knot tailwind component, as entered by the flight crew. Although in these cases the actual tailwind component is highlighted with white text on a red background, and the tailwind component limits are presented at the bottom of the display in white text on a black background, there is no indication that the stopping margin is not based on the presented tailwind component.

Analysis

AIRCRAFT Accident Report

Therefore, the Safety Board concludes that if the pilots had been presented with stopping margins associated with the input winds or had known that the stopping margins calculated by the OPC for the 737-700 already assumed credit for the use of thrust reversers, the pilots may have elected to divert.

Another OPC-programming factor observed by the Safety Board is that the airplane performance data programmed into the OPC by SWA was less conservative than the airplane performance data recommended by Boeing for braking action reports worse than good; this resulted in more favorable displayed stopping margins. Calculations performed using the Boeing-recommended data for a landing on runway 31C and the actual tailwind component of 8 knots showed that the airplane would require a longer landing distance than available under both fair and poor braking action conditions (an additional 260 and 2,070 feet beyond the departure end of the runway, respectively).$^{80}$ The Safety Board concludes that if Boeing's recommended airplane performance data were used in SWA's OPC calculations, the resulting negative stopping margins for even fair braking action conditions would have required the pilots to divert.

After this accident, SWA redesigned its arrival landing distance performance calculations to consistently reflect the assumption of two-engine reverse thrust and revised its OPC display to show the reverse thrust level assumed based on the conditions. Additionally, SWA modified its OPC display to consistently present output associated with the actual tailwind component. When the tailwind component exceeds authorized limits for landing (5 knots for poor braking action, 10 knots for good or fair braking action) a numeric stopping margin value is not presented. Finally, SWA amended its FOM guidance and policies regarding OPC reverse thrust assumptions to ensure consistency and to clarify the assumption of reverse thrust use across all 737 models. In response to this accident, the FAA issued SAFO 06012 to all turbojet operators, encouraging them to require pilots to perform arrival landing assessments if the weather conditions, runway, or airplane landing configuration has changed since the dispatch calculation and to train pilots regarding all aspects and assumptions used in these assessments. However, the Safety Board notes that operators are not required to comply with FAA guidance material such as this SAFO.$^{81}$

FAA advisory material regarding electronic flight performance calculations $^{82}$ suggests that the output be displayed in a manner that is understood easily and accurately and that users of such devices should be aware of any assumptions upon which the flight performance calculations are based. There is no specific guidance suggesting that these assumptions be as clear to pilots as similar information would be on a tabular chart, however. Such clarity is critical because airplane performance data and related OPC assumptions are not consistent across manufacturers, airplane models, or operators

Analysis

AIRCRAFT Accident Report

and may be based on information other than what the pilots entered. In the case of the accident flight, the SWA OPC screen did not display OPC assumptions (for example, the thrust reverser credit assumptions) when they were applicable; this information would have been readily available on a tabular chart. Therefore, the Safety Board concludes that presentation of the OPC assumptions upon which landing distance calculations are based is critical to a pilot's decision to land. Therefore, the Safety Board believes that the FAA should require all 14 CFR Part 121 and 135 operators to ensure that all on board electronic computing devices they use automatically and clearly display critical performance calculation assumptions.

As a result of its evaluation of the accident pilots' decision to land and their actions during the approach and landing, the Safety Board determined that if the pilots had been aware of existing company guidance and policies in several areas, including runway braking action reports and the underlying assumptions factored into OPC stopping margin calculations, they would have made a better-informed landing decision. Accident evidence indicated that other SWA pilots were similarly unaware of SWA's guidance and policies in these areas. Therefore, the Safety Board concludes that SWA did not provide its pilots with clear and consistent guidance and training regarding company policies and procedures in several areas, including interpretation of braking action reports and the assumptions affecting landing distance assessments. Therefore, the Safety Board believes that the FAA should require all 14 CFR Part 121 and 135 operators to provide clear guidance and training to pilots and dispatchers regarding company policy on surface condition and braking action reports and the assumptions affecting landing distance/stopping margin calculations, to include use of airplane ground deceleration devices, wind conditions and limits, air distance, and safety margins.

2.2.3 Thrust Reverser Usage and Autobrakes

According to SWA procedures, the flying pilot was required to deploy the thrust reversers as soon as possible after nosewheel touchdown for all landings. SWA guidance especially emphasized immediate deployment of reverse thrust when braking actions were reported to be less than good. The accident pilots reported that they were aware of the company's reverse thrust policies and routinely carried them out; however, for the accident landing, the captain (the flying pilot) did not deploy reverse thrust immediately after the airplane touched down. During postaccident interviews, the captain stated that he tried to deploy the thrust reversers promptly after touchdown but was not successful. SWA procedures also required the monitoring pilot to be attentive for procedural deviations during all landings. The first officer stated that, when he realized that the captain had not deployed the thrust reversers, he moved the thrust levers to command reverse thrust (thrust reverser activation was initiated about 15 seconds after touchdown according to FDR data). FDR data indicated that the thrust reversers were eventually fully deployed about 18 seconds after touchdown, and the pilots held maximum reverse thrust until the airplane came to a stop off the end of the runway.

The Safety Board's review of FDR data from four SWA 737s that landed and came to a stop on runway 31C at MDW during the 21 minutes before the accident indicated

Analysis

AIRCRAFTAccident Report

that reverse thrust on these airplanes was deployed promptly after landing. Postaccident calculations showed that, if the pilots had promptly initiated and maintained maximum reverse thrust throughout the landing roll, the airplane would not have run off the end of the runway. Therefore, the Safety Board concludes that the pilots would have been able to stop the airplane on the runway if they had commanded maximum reverse thrust promptly after touchdown and maintained maximum reverse thrust to a full stop.

Despite the captain’s reported difficulties in his initial attempt to deploy the thrust reversers, they extended normally in a coordinated manner for the first officer. The captain’s seat position was the same as he routinely used, and the CVR recorded no comments or utterances indicating that the pilots were having difficulty with the thrust reverser levers. Further, postaccident examination of the throttle quadrant and reverse thrust systems provided no evidence of mechanical irregularity or failure; the levers were in a position to be deployed at any time during the landing rollout. In addition, postaccident interviews with other SWA pilots indicated that most had not experienced any difficulty deploying the thrust reversers, nor had they heard of others doing so, aside from occasionally not waiting long enough at the interlock position. Any difficulties that were described by SWA pilots were reportedly resolved immediately upon second attempt.$^{83}$ Finally, the pilots who had flown the accident airplane for the 10 flights before the accident reported experiencing no difficulties in deploying the thrust reversers in that airplane. Therefore, the Safety Board concludes that the pilots’ delay in deploying the thrust reversers cannot be attributed to mechanical or physical difficulties.

SWA planned to implement a new policy the week after the accident that would have required the use of autobrakes during landings under some conditions, including the accident landing conditions.$^{84}$ In preparation, SWA provided its pilots with a self-study training module on the system and related procedures. Despite having completed the training module, neither of the accident pilots had previous operational experience with autobrakes. Information from the CVR indicates that although both pilots expressed concern, the captain, in particular, was hesitant to use the autobrakes for the first time in the weather and runway conditions that existed for the accident landing. The pilots discussed possible contingencies (for example, autobrake failure, loss of directional control, and reversion to manual braking). They ultimately agreed that use of the autobrakes would allow them to stop in the shortest distance and used the autobrakes on maximum setting during the accident landing.

Use of autobrakes when landing on short or slippery runways required a change in the sequence of landing tasks for both the flying pilot and the monitoring pilot. Before

Analysis

AIRCRAFTAccident Report

SWA's new autobrakes procedures took effect, procedures required the flying pilot to manually apply wheel brakes and deploy the thrust reversers simultaneously as soon as possible after touchdown. However, with the use of autobrakes, only one of these two tasks was required at touchdown; the prompt manual application of wheel brakes was no longer necessary. Research indicates that carrying out new procedures requires more effort and cognitive resources than does carrying out routine procedures and limits the number of tasks that can be carried out simultaneously.$^{85}$ Because of the pilots' concerns regarding the autobrakes and their unfamiliarity with the system's operation, it would have been natural for them to focus on the autobrake system's performance after the airplane touched down.

During postaccident interviews, both pilots reported that they were preoccupied by the autobrake system during the accident landing. The captain reported that his focus on the autobrake system performance distracted him from trying to deploy the thrust reversers again after his first attempt was unsuccessful. The first officer had the additional task of monitoring the autobrakes light on the front instrument panel during the landing rollout, although he reported that he maintained his focus outside of the cockpit and on their stopping performance. Research also indicates that activities that have been grouped together in an automatic task sequence require substantial effort to separate. 86 In this case, applying the wheel brakes would normally be accomplished with deployment of the thrust reversers, and omitting one of these linked activities (wheel brakes) could help explain omission of the other (thrust reversers). The pilots stated that, as the landing roll continued, they were not satisfied with the airplane's deceleration, and FDR data indicated that, about 12 seconds after touchdown, they transitioned from autobrakes to maximum manual wheel braking. FDR data indicated that the thrust reversers deployment was initiated 15 seconds after touchdown, with full thrust reverser deployment occurring 18 seconds after touchdown.

According to postaccident interviews with SWA personnel, similar distractions were observed in SWA pilots during the development of the company's autobrake program. SWA check airmen and their first officers reported concern prior to use and difficulty with the transition from using autobrakes to manual braking after touchdown; some were so distracted that they delayed reverse thrust application. Pilots also indicated that these challenges persisted for the first few landings only, until they had the chance to acclimate to the new procedures. At the time of the accident, SWA's planned implementation of its autobrakes procedures did not include a familiarization period with the use of the

Analysis

AIRCRAFT Accident Report

autobrakes,$^{87}$ nor was one required by regulations.$^{88}$ However, feedback from other SWA pilots should have alerted SWA management and the company's FAA POI to the need for a familiarization or transition period.

The Safety Board concludes that the pilots' first use of the airplane's autobrake system during a challenging landing situation led to the pilots' distraction from the otherwise routine task of deploying the thrust reversers promptly after touchdown. Had SWA implemented an autobrake familiarization period in advance, such a period would have allowed pilots to become comfortable with the changed sequence of landing tasks. The Safety Board further concludes that the implementation of procedures requiring thrust reverser status confirmation immediately after touchdown may prevent pilots from inadvertent failure to deploy the thrust reversers after touchdown. Therefore, the Safety Board believes that the FAA should require all Part 121 and 135 operators of thrust reverser-equipped airplanes to incorporate a procedure requiring the non-flying (monitoring) pilot to check and confirm the thrust reverser status immediately after touchdown on all landings.

The Safety Board notes that the timing and nature of this autobrake policy change was specific to SWA, based on its operation of a fleet of only one model airplane (the 737) and the company's desire to implement the policy simultaneously throughout that fleet. After this accident, the company voluntarily amended its autobrake policy and training program, delaying the implementation date and requiring a familiarization period, which allowed SWA pilots to first use the autobrakes in good conditions and with large stopping margins.$^{89}$ In addition, SWA provided its pilots with specific instructions that the monitoring pilot was to monitor the reverse thrust levers during the landing sequence and to make a specific callout in the event of deviation from SWA reverse thrust procedures.

2.3 Landing Distance Assessments

Preflight landing distance calculations (assessments) are required by Federal regulation while arrival landing distance calculations (assessments) are not. This section discusses the differences between preflight and arrival landing distance calculations and evaluates the need for both. This section also discusses related content in the FAA's proposed OpSpec, recent SAFO, and observed industry landing distance practices.

Analysis

AIRCRAFT Accident Report

2.3.1 Preflight and Arrival Landing Distance Calculations/ Assessments

The FAA requires Part 121 operators to perform preflight landing distance calculations before they depart on a flight, in part, to determine the maximum takeoff weight at which the airplane can depart, travel to the destination, and safely land on the available landing distance at the destination and/or alternate airport. Although preflight landing distance assessments are standardized by Federal regulations, the assessments do not attempt to comprehensively account for the actual conditions, configuration, and pilot techniques that exist and/or occur at the time of arrival.$^{90}$ The manufacturer's flight test data upon which these calculations are based are primarily accumulated during demonstrated landings on a dry, smooth, hard-surfaced runway without the effects of reverse thrust. To account for variations in landing conditions, pilot techniques, and other operational uncertainties, the FAA requires operators to factor in a significant safety margin in excess of the demonstrated landing distance during their preflight landing distance assessments.$^{91}$ The Safety Board's review of SWA dispatch documents for the accident flight indicated that, based on preflight calculations, the accident airplane was legal to depart BWI intending to land at MDW.

Arrival landing distance assessments assist pilots in ensuring that they will be able to land the airplane and safely stop on the intended runway given the arrival weather and runway surface conditions and the planned airplane configuration, landing technique, and use of deceleration devices. Like preflight landing distance calculations, arrival landing distance calculations/assessments are typically developed by an operator or contractor based on data provided by the manufacturer. However, unlike the preflight data, specific FAA approval is not required for the data used by operators in their arrival landing distance assessments because those assessments are not required.

Although the FAA does not require operators to perform arrival landing distance assessments, many Part 121 operators (including SWA) do require their pilots to perform landing distance assessments before every landing. However, because the FAA does not require or standardize arrival assessments as it does preflight assessments, operators are allowed to set their own policies and use data from various sources (for example, the manufacturer, in-house personnel, an outside contractor, etc.). Depending on the source, the data used may be less conservative than the manufacturer's data and may contain embedded assumptions related to landing and deceleration techniques, the airplane's braking ability for a given runway surface condition report, and/or the application of additional safety margins. If pilots are unaware of these embedded assumptions, they might believe that they need less landing distance than they actually do or have an inaccurate perception of how much braking effort will be needed on landing. Depending on an operator's policies, pilots may not be required to conduct arrival landing assessments; may conduct such assessments based on variable landing performance data sources,

Analysis

AIRCRAFTAccident Report

assumptions, and calculation methods; or may conduct such assessments based on data that include no additional safety margin.

SWA required its pilots to perform arrival landing distance assessments for each landing and developed a system, primarily based on Boeing's performance data, to account for actual conditions and planned procedures/techniques. However, FAA personnel did not approve the data or calculation methods developed by SWA. The resultant system used data that were less conservative than Boeing recommended for braking reports worse than good. Although SWA and FAA personnel were aware that actual arrival conditions cannot be perfectly defined, planned procedures cannot always be accomplished, and the resultant variations will not always yield a conservative safety margin, the data programmed into SWA's OPC did not account for reasonable operational variations. This is of particular concern because SWA's policies at the time of the accident and its new autobrake policy authorize landing with even the smallest of positive calculated stopping margins.

The Safety Board notes that, although not required by the FAA, SWA's arrival landing distance assessment practices exceeded those of many other operators; yet, the safety margin was inadequate to prevent this accident. The Safety Board notes that preflight safety margins alone may not be sufficient to ensure adequate stopping margins at arrival. This investigation has shown that an arrival landing distance assessment should be conducted before arrival and should incorporate the following six basic components:

● Approved aerodynamic performance data obtained from demonstrated flight test landings;

● A set of defined operational procedures and assumptions (for example, touchdown at 1,500 feet, reverse thrust deployment promptly after touchdown, etc.);

● Actual arrival condition data (weather, airplane configuration, runway surface condition, etc.);

● A physics-based method for calculating airplane performance;

● A minimum acceptable standard for correlating the airplane's braking ability to the runway surface condition; and

● A minimum acceptable safety margin/factor that accounts for reasonable operational variations and uncertainties.

At the time of the accident, SWA had incorporated the first four components into their arrival landing distance assessments and prescribed the fifth component. After the accident, SWA incorporated the sixth component by adding an additional 15 percent safety margin to account for operational variations and uncertainties into its arrival landing distance assessments.

Analysis

AIRCRAFT Accident Report

2.3.2 Safety Alert for Operators Discussion and Industry Practice

Regarding Landing Distance Assessments

As previously noted, although the FAA is on record as advocating arrival landing distance assessments, there is currently no requirement, FAA-approved data, minimum correlation standards, or minimum safety margin for such assessments. As a result, operators remain free to choose whether and how they perform such assessments.

As a result of the SWA flight 1248 accident, the Safety Board issued urgent Safety Recommendation A-06-16, which asked the FAA to prohibit all 14 CFR Part 121 operators from using reverse thrust credit in landing performance calculations. The stated intent of this recommendation was to ensure adequate landing safety margins on contaminated runways. In response, in June 2006, the FAA issued an advance notice of its intent to issue mandatory OpSpec N 8400.C082, which would have required all Part 121, 135, and 91 subpart K turbojet operators to conduct landing performance assessments (not necessarily a specific calculation) before every arrival based, in part, on planned touchdown point, procedures and data at least as conservative as the manufacturer's, updated wind and runway conditions, and an additional 15 percent safety margin. However, the FAA subsequently decided not to issue the mandatory OpSpec at that time and, in August 2006, published SAFO 06012 as an interim guidance measure. SAFO 06012 addressed similar issues to the mandatory OpSpec, but operator compliance with the SAFO is, by definition, voluntary. Although the FAA published SAFO 06012 with the intent of pursuing rulemaking in the area of landing distance assessments, in the interim, operators are still not required to comply with its recommendations and, currently, many operators do not.

For example, on February 18, 2007, a Shuttle America Embraer ERJ-170 ran off the end of snow-contaminated runway 28 at Cleveland Hopkins International Airport, Cleveland, Ohio.$^{92}$ The investigation to date has revealed that Shuttle America did not require its pilots to perform (and therefore did not incorporate landing distance safety margins into) arrival landing distance assessments. About 2 months later, a Pinnacle Airlines Bombardier Regional Jet CL600-2B19 ran off the end of snow-covered runway 28 at Cherry Capital Airport in Traverse City, Michigan.$^{93}$ By contrast, the investigation into this accident showed that Pinnacle's OpSpecs required its pilots to perform arrival landing distance assessments (including a minimum 15 percent safety margin) per SAFO 06012,$^{94}$ however, the pilots did not perform the required assessment before the accident landing. If an arrival landing distance assessment had been performed, given the existing conditions, Pinnacle's OpSpecs would have dictated that a diversion was required.

Analysis

AIRCRAFT Accident Report

The Safety Board is concerned that, because of operational and conditional variations, it is possible for an airplane to use more of the landing runway than preflight (dispatch) calculations predicted and for pilots to continue to run off the end of contaminated runways. During a January 2007 meeting, Safety Board, FAA, Boeing, SWA, and SWAPA personnel discussed landing distance assessment and runway surface condition issues. A subsequent Boeing document recommended that operators develop arrival landing distance assessment procedures for their flight crews to use to better ensure that a full-stop landing can be made on the arrival runway in the conditions existing at the time of arrival (weather and runway) and with the deceleration means and airplane configuration to be used, consistent with SAFO 06012. The circumstances of the flight 1248 accident (among others) demonstrate that conditions $^{95}$ can change between dispatch and arrival and that there is a safety benefit to landing distance assessments at both times.

The Safety Board notes that the FAA concluded in SAFO 06012 that operator compliance with preflight landing distance planning requirements alone “does not ensure that the airplane can safely land within the distance available on the runway in the conditions that exist at the time of arrival, particularly if the runway, runway surface condition, meteorological conditions, airplane configuration, airplane weight, or use of airplane ground deceleration devices is different than that used in the preflight calculation.” In addition, the FAA stated that “a landing distance assessment should be made under the conditions existing at the time of arrival in order to support a determination of whether conditions exist that may affect the safety of the flight and whether operations should be restricted or suspended.”

2.3.3 Landing Distance Assessments Summary

Existing FAA regulations do not specify either the type of arrival landing distance assessment that should be performed or specify a safety margin that should be applied. The FAA-advocated minimum safety margin of 15 percent for arrival landing distance assessments published in SAFO 06012 is based on historic links to the FAA-mandated additional 15 percent factor for wet/slippery preflight planning requirements and the 15 percent factor embedded in the EASA and JAA operational requirements for contaminated runway landing performance. Although during public hearing testimony the FAA stated that the 15 percent landing safety margin has not been substantiated by a specific data collection and evaluation effort, the Safety Board is convinced that a defined landing safety margin is necessary for air carrier operations on contaminated runways. The Board was encouraged when the FAA proposed OpSpec N 8400.C082, which would have required operators of transport-category airplanes to incorporate a 15 percent safety margin in arrival landing distance calculations. The proposed 15 percent safety margin identified in FAA OpSpec N 8400.C082 would have satisfied the intent of Safety Recommendation A-06-16. However, the FAA subsequently sought voluntary operator implementation of such actions through SAFO 06012; although SAFO 06012 contains

Analysis

AIRCRAFT Accident Report

similar information to OpSpec N 8400.C082, compliance with the SAFO is not required by the FAA.$^{96}$

Because the FAA has not required actions to address the Board's urgent safety recommendation, flight crews of transport-category airplanes may still be permitted to land in wet, slippery, or contaminated runway conditions, without performing arrival landing distance assessments that incorporate adequate safety margins. As another winter season approaches, the urgent need for such margins becomes more critical. The Safety Board concludes that because landing conditions may change during a flight, preflight landing assessments alone may not be sufficient to ensure safe stopping margins at the time of arrival; arrival landing distance assessments would provide pilots with more accurate information regarding the safety of landings under arrival conditions. Further, the Safety Board concludes that although landing distance assessments incorporating a landing distance safety margin are not required by regulation, they are critical to safe operation of transport-category airplanes on contaminated runways. Therefore, the Safety Board believes that the FAA should require all 14 CFR Part 121, 135, and 91 subpart K operators to accomplish arrival landing distance assessments before every landing based on a standardized methodology involving approved performance data, actual arrival conditions, a means of correlating the airplane's braking ability with runway surface conditions using the most conservative interpretation available, and including a minimum safety margin of 15 percent. The Board recognizes that development of such a standardized methodology will take time. Therefore, the Safety Board further believes that, until a standardized methodology as described in the previous recommendation can be developed, the FAA should immediately require all 14 CFR Part 121, 135, and 91 subpart K operators to conduct arrival landing distance assessments before every landing based on existing performance data, actual conditions, and incorporating a minimum safety margin of 15 percent. Because the objectives of this recommendation and Safety Recommendation A-06-16 are identical, the Safety Board classifies A-06-16 "Closed—Unacceptable Action/Superceeded." Because the FAA has had adequate time to require landing distance assessments and implement a landing distance safety margin, but has not, A-06-16 was classified "Open—Unacceptable Response" on May 8, 2007. The superceding safety recommendation will maintain the status of "Open—Unacceptable Response."

Analysis

AIRCRAFT Accident Report

2.4 Runway Surface Condition Assessments

The Safety Board has long been concerned about runway surface condition assessment issues.$^{97}$ During this investigation, the Safety Board reevaluated the three methods currently used to assess a runway's surface condition before landing: 1) pilot braking action reports, 2) runway contaminant type and depth observations, and 3) ground surface vehicle friction measurements. The Board notes that all three methods have limitations and that, regardless of the method used, runway surface conditions may vary over time because of changes in precipitation, accumulation, traffic, direct sunlight, temperature, or as a result of runway maintenance/treatment. The Board further notes that no standardized and universally accepted correlation exists to define the relationship between the runway surface condition (using any of the three runway surface assessment methods) and an airplane's braking ability.

This section discusses the accuracy and limitations associated with each method of runway surface condition assessment. Pilot braking action reports, contaminant type and depth reports, and airport runway surface friction measuring devices are discussed in sections 2.4.1, 2.4.2, and 2.4.3, respectively. Runway surface condition assessments are summarized in section 2.4.4, and correlating runway surface condition to airplane landing performance/braking ability is discussed in section 2.4.5.

2.4.1 Braking Action Reports

Pilot braking action reports are commonly used by arriving pilots to predict landing runway conditions. However, Safety Board safety recommendation communications, public hearing testimony, and flight 1248 accident evidence indicate that pilot braking action reports are subjective and can vary significantly depending on the reporting pilot's experience level and the type of airplane in use.

The FAA has frequently acknowledged (most recently in SAFO 06012) that pilot braking action reports are subjective and reflect individual pilot expectations, perceptions, and experiences. Further, braking action reports are sensitive to airplane type and the actual deceleration methods used to slow or stop the airplane. In addition, an arriving pilot may have to interpret mixed pilot braking action reports (for example, fair-to-poor braking action reported on a landing runway) or conflicting runway condition

Analysis

AIRCRAFT Accident Report

reports (for example, a pilot braking action report that conflicts with a runway friction measurement).$^{98}$

In SAFO 06012, the FAA defined a reliable braking action report as a braking action report submitted from a turbojet airplane with landing performance capabilities similar to those of the airplane being operated. The FAA recommends in the SAFO that pilots should use all available information and make decisions based on experience and sound judgment; however, the FAA has not yet provided standardized procedures or specific criteria for pilots to use in the development and delivery of braking action reports.$^{99}$

Since this accident, the FAA has hosted an industry workshop that attempted to address this issue. A mid-2006 industry working group produced guidance regarding runway surface condition assessments that has since been disseminated to all operators of Boeing turbojet airplanes in an August 2007 bulletin. SWA is incorporating the working group guidance into its materials and training and plans to publish related revisions in October 2007 (see figure 6).$^{100}$

2.4.2 Contaminant Type and Depth

A field report or observation of the type and depth of contaminant on the runway, typically conducted by airport personnel, may also be used to assess the runway surface condition. However, these observations may also be subjective and dependent on the observer's experience and vantage point, the timing of the observation, and rapidly changing conditions. The FAA has not established and defined a standard correlation between an airplane's braking ability and reports of contaminant type and depth.

The Safety Board notes, however, that many airplane manufacturers worldwide (for example, Airbus and Embraer) provide their operators with contaminant type and depth options for landing distance calculations. Further, European agencies (EASA and JAA) require operators to account for contaminated runway conditions and define a minimally acceptable standard that manufacturers can use to correlate contaminant type and depth to airplane landing performance. In practice (and as stated in SAFO 06012), the FAA considers the data developed for showing compliance with EASA and JAA contaminated runway certification or operating requirements acceptable for U.S. arrival landing distance assessments.

Analysis

AIRCRAFTAccident Report

2.4.3 Airport Runway Surface Friction Measuring Devices

Runway friction measuring devices were originally developed for use by airports for runway maintenance purposes and were not intended for use in assessing airplane landing performance. Although the FAA funds purchase of these devices for airports and believes that measurements are useful in identifying trends in runway surface condition, FAA representatives have stated that these devices cannot be reliably correlated with airplane performance or pilot braking action reports. Specifically, FAA statements and testimony at the Safety Board's public hearing on this accident indicate that ground surface vehicle friction measurements should not be used to predict airplane stopping performance, in part, because of 1) unresolved variability in equipment design and calibration; 2) changes over time in temperature, sunlight, precipitation, accumulation, and operating traffic; and 3) the results of maintenance and/or treatment of a runway.

MDW friction readings were less conservative than the available braking action reports and the postaccident calculated runway 31C surface condition. The runway 31C friction measurement taken at MDW 30 minutes before the accident landing (immediately after the most recent runway cleaning) was 0.67, which a Transport Canada public hearing witness correlated with expected "bare and dry" runway surface condition performance. A measurement taken just after the accident was 0.40, which was considered fairly good according to a public hearing witness from NASA. According to CRFI data for various runway surface conditions, both measurements (0.67 and 0.40) were within the range of normal values observed with 3 mm or less of loose snow on the runway. Measurements for this surface condition ranged from 0.16 to 0.76 (see figure 7 in section 1.18.2.2.1). The broad range of measurements possible with a single contaminant demonstrates that this type of runway friction measurement device cannot reliably be used to predict airplane stopping performance under these contaminant conditions (3 mm or less of loose snow).

The Safety Board has previously issued safety recommendations supporting efforts to correlate friction measurement device readings to airplane performance. Boeing does not attempt to correlate runway friction measurements to airplane performance; however, many operators (including SWA) have developed tables that correlate friction measurements to braking action reports. Internationally, Transport Canada provides CRFI tables that correlate ground surface vehicle friction survey measurements to airplane performance for certain contamination conditions; however, use of the CRFI is optional. The Canadian academic community and members of the international research community also support the use of the IRFI, which is not fully operational or widely supported by the aviation industry. For both the CRFI and the IRFI, runway friction measurements are subject to contaminant type and depth constraints.

2.4.4 Runway Surface Condition Assessments Summary

The Safety Board concludes guidance on braking action and contaminant type and depth reports would assist pilots, ATC, operator dispatch, and airport operations personnel in minimizing the subjectivity and standardization shortcomings of such reports. Further, the Safety Board concludes that using the most conservative interpretation of runway

Analysis

AIRCRAFT Accident Report

braking action or surface condition reports from mixed or conflicting reports (for example, a fair-to-poor braking action report or a pilot braking action report that conflicts with a runway friction measurement) would increase the landing safety margin. Therefore, the Safety Board believes that the FAA should develop and issue formal guidance regarding standards and guidelines for the development, delivery, and interpretation of runway surface condition reports.

2.4.5 Correlating Runway Surface Condition to Airplane Landing Performance

The Safety Board is concerned that the FAA currently provides no minimally acceptable standard for U.S. operators to use to correlate runway surface condition reports to airplane braking ability.$^{101}$ Although a draft AC, dated August 1989, proposed a correlation between runway condition (braking action) and an airplane's braking ability, the FAA never published it. SAFO 06012, issued by the FAA in 2006, also advocated the use of a specific correlation between reported braking action and runway contaminant type and depth to predict turbojet landing/stopping performance but only if the manufacturer-supplied wet or contaminated runway data were unavailable.

Operators need a method to relate any of the three runway surface condition reports and airplane braking ability to determine an airplane's landing performance. However, because the FAA has defined no acceptable correlation standards, manufacturers, operators, and/or third-party suppliers develop their own standards to fulfill their needs.$^{102}$ This practice results in variable estimates of an airplane's actual landing performance capability and different landing safety margins being used across even operators of the same make and model airplane. The Safety Board notes that flight crews preparing to land similar airplanes on similar runways, under similar actual conditions should not obtain arrival landing distance results that permit one flight crew to land while the other flight crew cannot, based solely on the operator's choice of how to correlate a runway surface condition report to the airplane's braking ability.

Further, required arrival landing distance assessments should include an additional safety margin to account for variations in actual landing conditions and operational techniques. The current lack of standards in manufacturer-supplied and operator-packaged arrival landing data complicates the validation of both the airplane's basic landing performance capability and adequate safety margins. The Safety Board's investigation of this accident revealed arrival landing distance implementation errors that resulted in latent safety risks at two air carriers. The Safety Board concludes that an

Analysis

AIRCRAFT Accident Report

adequate safety margin would account for operational variations and uncertainties when factored into arrival landing distance assessments. Further, the Safety Board concludes that establishment of a means of correlating the airplane's braking ability with the runway surface condition would provide a more accurate assessment of the airplane's basic landing performance capability. Therefore, the Safety Board believes that the FAA should establish a minimum standard for 14 CFR Part 121 and 135 operators to use in correlating an airplane's braking ability to braking action reports and runway contaminant type and depth reports for runway surface conditions worse than bare and dry.

2.5 Airplane-Based Friction Measurements

The circumstances of this accident demonstrate the need for a method of quantifying the runway surface condition in a more meaningful way to support airplane landing performance calculations.$^{103}$ The Safety Board and industry practice of analyzing an airplane's actual landing performance in the aftermath of an accident based on airplane-recorded data demonstrates that runway surface condition and braking effectiveness information can be extracted from recorded data.$^{104}$ These practices have shown that if the necessary parameters are recorded, specific calculations and operational procedures performed at lower rollout speeds (for example, wheel brake application for several seconds below 60 knots) can be used to quantify the runway surface condition and estimate the airplane's potential braking ability.$^{105}$ Thus, airplane braking coefficient/ runway surface condition data derived from one type of landing airplane could be used to estimate another type of airplane's braking ability and landing distance.$^{106}$

During a postaccident meeting in January 2007, Boeing, FAA, SWA, and SWAPA personnel agreed that this approach to obtain runway surface condition and braking effectiveness data has technical merit. However, the technical and operational feasibility issues associated with an airplane-based friction measurement system have not been evaluated on a test bed or an in-service air carrier airplane to date. A measurement

Analysis

AIRCRAFT Accident Report

system installed on in-service airplanes could provide runway surface condition data that would surpass information produced by methods currently in use (including ground friction surveys, pilot braking action reports, and type and depth reports), without interfering with traffic flow. Such a system could provide unparalleled runway surface condition quantification and trend information of direct use to pilots, ATC, and airport maintenance.

The Safety Board concludes that development and implementation of an operationally feasible, airplane-based, airplane braking ability/runway surface condition measurement and communication system would provide high value information to subsequent landing airplanes; the benefits of such a system during inclement weather would likely meet or exceed all existing runway surface condition reporting systems, with no resultant interruption to traffic operations. Therefore, the Safety Board believes that the FAA should demonstrate the technical and operational feasibility of outfitting transport-category airplanes with equipment and procedures required to routinely calculate, record, and convey the airplane braking ability required and/or available to slow or stop an airplane during the landing roll. If feasible, the FAA should also require operators of transport-category airplanes to incorporate use of such equipment and related procedures into their operations.

2.6 Runway Safety Areas

The Safety Board's investigation of this accident revealed that FAA and MDW airport personnel had been discussing RSA improvements off the ends of MDW runways for about 5 years before the accident; however, no such improvements had been made when the accident occurred. Correspondence between the FAA and MDW personnel indicated that the option of acquiring land to develop dimensionally standard RSAs (which would extend 1,000 feet beyond the ends of the MDW runways) was determined to be both undesirable $^{107}$ and economically infeasible. Further, realigning the runways on the available airport property was not possible, and shortening the runways to improve RSAs was not practical given the operational requirements of the airplanes operating at MDW.

A practicability study contracted by MDW concluded that insufficient space existed for standard EMAS installations off the ends of MDW runways. The study did not address nonstandard EMAS installations, and, throughout most of the FAA/MDW correspondence, the FAA did not reference the installation of nonstandard EMAS beds off the end of MDW runways. However, although the FAA had no official guidance regarding nonstandard EMAS installations until 2005, agency personnel were aware of the feasibility of such installations and had approved nonstandard EMAS installations at several other airports at the time of the accident. The Board's postaccident calculations indicated that even a nonstandard EMAS installation off the end of runway 31C at MDW would have stopped the accident airplane before it left airport property and thus would have prevented the collision with the automobile.

Analysis

AIRCRAFT Accident Report

Therefore, the Safety Board concludes that the absence of an EMAS installation in the limited overrun area for runway 31C contributed to the severity of the accident; even a nonstandard EMAS installation would have safely stopped the airplane before it left airport property. After the accident, the FAA approved the installation of nonstandard EMAS beds at the ends of runways 31C, 13C, 4R, and 22L at MDW. By early December 2006, the first portion (170 feet long and 170 feet wide) of an EMAS bed had been installed off the departure end of runway 31C, with an additional, 40-foot long portion planned. Airport and City officials indicated that the installation of EMAS beds at the ends of affected MDW runways would be completed by winter 2007, pending relocation of localizer antennas at the ends of runways 13C, 4R, and 22L.

AIRCRAFT Accident Report

3. CONCLUSIONS

3.1 Findings

1. The pilots were properly certified and qualified under Federal regulations. No evidence indicated any medical or behavioral conditions that might have adversely affected their performance during the accident flight. There was no evidence of flight crew fatigue.

1. The accident airplane was properly certified and was equipped, maintained, and dispatched in accordance with industry practices.

1. No evidence indicated any failure of the airplane's powerplants, structures, or systems that would have affected the airplane's performance during the accident landing.

1. The pilots had adequate initial and updated meteorological information throughout the flight.

1. Chicago Midway International Airport personnel monitored runway conditions and provided appropriate snow removal service on the night of the accident.

1. The Chicago Midway International Airport air traffic control tower controller did not follow Federal Aviation Administration guidance when he did not provide all of the required braking action report information.

1. Because the pilots did not use the more critical braking action term (poor) during their arrival landing distance assessment (which, combined with the associated tailwind limitation, would have required them to divert), they were not in compliance with Southwest Airlines' policies.

1. If the pilots had been presented with stopping margins associated with the input winds or had known that the stopping margins calculated by the on board performance computer for the 737-700 already assumed credit for the use of thrust reversers, the pilots may have elected to divert.

1. If Boeing's recommended airplane performance data were used in Southwest Airlines' on board performance computer calculations, the resulting negative stopping margins for even fair braking action conditions would have required the pilots to divert.

1. Presentation of the on board performance computer assumptions upon which landing distance calculations are based is critical to a pilot's decision to land.

1. Southwest Airlines did not provide its pilots with clear and consistent guidance and training regarding company policies and procedures in several areas, including

Conclusions

AIRCRAFT Accident Report

interpretation of braking action reports and the assumptions affecting landing distance assessments.

1. The pilots would have been able to stop the airplane on the runway if they had commanded maximum reverse thrust promptly after touchdown and maintained maximum reverse thrust to a full stop.

1. The pilots' delay in deploying the thrust reversers cannot be attributed to mechanical or physical difficulties.

1. The pilots' first use of the airplane's autobrake system during a challenging landing situation led to the pilots' distraction from the otherwise routine task of deploying the thrust reversers promptly after touchdown. Had Southwest Airlines implemented an autobrake familiarization period in advance, such a period would have allowed pilots to become comfortable with the changed sequence of landing tasks.

1. The implementation of procedures requiring thrust reverser status confirmation immediately after touchdown may prevent pilots from inadvertent failure to deploy the thrust reversers after touchdown.

1. Because landing conditions may change during a flight, preflight landing assessments alone may not be sufficient to ensure safe stopping margins at the time of arrival; arrival landing distance assessments would provide pilots with more accurate information regarding the safety of landings under arrival conditions.

1. Although landing distance assessments incorporating a landing distance safety margin are not required by regulation, they are critical to safe operation of transport-category airplanes on contaminated runways.

1. Guidance on braking action and contaminant type and depth reports would assist pilots, air traffic control, operator dispatch, and airport operations personnel in minimizing the subjectivity and standardization shortcomings of such reports.

1. Using the most conservative interpretation of runway braking action or surface condition reports from mixed or conflicting reports (for example, a fair-to-poor braking action report or a pilot braking action report that conflicts with a runway friction measurement) would increase the landing safety margin.

1. An adequate safety margin would account for operational variations and uncertainties when factored into arrival landing distance assessments.

1. Establishment of a means of correlating the airplane's braking ability with the runway surface condition would provide a more accurate assessment of the airplane's basic landing performance capability.

1. Development of an operationally feasible, airplane-based, airplane braking ability/ runway surface condition measurement and communication system would provide

Conclusions

AIRCRAFT Accident Report

high value information to subsequent landing airplanes; the benefits of such a system during inclement weather would likely meet or exceed all existing runway surface condition reporting systems, with no resultant interruption to traffic operations.

1. The absence of an engineering materials arresting system (EMAS) installation in the limited overrun area for runway 31C contributed to the severity of the accident; even a nonstandard EMAS installation would have safely stopped the airplane before it left airport property.

3.2 Probable Cause

The National Transportation Safety Board determines that the probable cause of this accident was the pilots' failure to use available reverse thrust in a timely manner to safely slow or stop the airplane after landing, which resulted in a runway overrun. This failure occurred because the pilots' first experience and lack of familiarity with the airplane's autobrake system distracted them from thrust reverser usage during the challenging landing.

Contributing to the accident were Southwest Airlines' 1) failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations; 2) programming and design of its on board performance computer, which did not present inherent assumptions in the program critical to pilot decision-making; 3) plan to implement new autobrake procedures without a familiarization period; and 4) failure to include a margin of safety in the arrival assessment to account for operational uncertainties. Also contributing to the accident was the pilots' failure to divert to another airport given reports that included poor braking actions and a tailwind component greater than 5 knots. Contributing to the severity of the accident was the absence of an engineering materials arresting system, which was needed because of the limited runway safety area beyond the departure end of runway 31C.

AIRCRAFTAccident Report

4. RECOMMENDATIONS

4.1 New Recommendations

As a result of this investigation, the National Transportation Safety Board makes the following recommendations to the Federal Aviation Administration:

Immediately require all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators to conduct arrival landing distance assessments before every landing based on existing performance data, actual conditions, and incorporating a minimum safety margin of 15 percent. (A-07-57) Urgent (Supercedes Safety Recommendation A-06-16 and classified "Open-Unacceptable Response.")

Require all 14 Code of Federal Regulations Part 121 and 135 operators to ensure that all on board electronic computing devices they use automatically and clearly display critical performance calculation assumptions. (A-07-58)

Require all 14 Code of Federal Regulations Part 121 and 135 operators to provide clear guidance and training to pilots and dispatchers regarding company policy on surface condition and braking action reports and the assumptions affecting landing distance/stopping margin calculations, to include use of airplane ground deceleration devices, wind conditions and limits, air distance, and safety margins. (A-07-59)

Require all 14 Code of Federal Regulations Part 121 and 135 operators of thrust reverser-equipped airplanes to incorporate a procedure requiring the non-flying (monitoring) pilot to check and confirm the thrust reverser status immediately after touchdown on all landings. (A-07-60)

Require all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators to accomplish arrival landing distance assessments before everylanding based on a standardized methodology involving approved performance data, actual arrival conditions, a means of correlating the airplane's braking ability with runway surface conditions using the most conservative interpretation available, and including a minimum safety margin of 15 percent. (A-07-61)

Develop and issue formal guidance regarding standards and guidelines for the development, delivery, and interpretation of runway surface condition reports. (A-07-62)

Recommendations

AIRCRAFT Accident Report

Establish a minimum standard for 14 Code of Federal Regulations Part 121 and 135 operators to use in correlating an airplane's braking ability to braking action reports and runway contaminant type and depth reports for runway surface conditions worse than bare and dry. (A-07-63)

Demonstrate the technical and operational feasibility of outfitting transport-category airplanes with equipment and procedures required to routinely calculate, record, and convey the airplane braking ability required and/or available to slow or stop the airplane during the landing roll. If feasible, require operators of transport-category airplanes to incorporate use of such equipment and related procedures into their operations. (A-07-64)

4.2 Previously Issued Recommendation Resulting From This Accident Investigation and Classified in this Report

As a result of the SWA flight 1248 accident investigation, the Safety Board issued the following urgent safety recommendation to the FAA on January 27, 2006:

Immediately prohibit all 14 Code of Federal Regulations Part 121 operators from using reverse thrust credit in landing performance calculations. (A-06-16)

This recommendation (previously classified “Open–Unacceptable Response” on May 8, 2007) is classified “Closed–Unacceptable Action/Superceded” by Safety Recommendation A-07-57 in section 2.3 of this report.

BY THE NATIONAL TRANSPORTATION SAFETY BOARD

Mark V. Rosenker

Chairman

Deborah A. P. Hersman

Member

Robert L. Sumwalt

Vice Chairman

Kathryn O'Leary Higgins

Member

Steven R. Chealander

Member

Adopted: October 2, 2007

AIRCRAFT Accident Report

5. APPENDIXES

APPENDIX A

INVESTIGATION AND PUBLIC HEARING

Investigation

The National Transportation Safety Board was notified about the accident on December 8, 2005, shortly after it occurred. A full go-team arrived at the accident scene early the next morning. The go-team was accompanied by representatives from the Safety Board's Office of Transportation Disaster Assistance and Public Affairs and by then Chairman-designee Ellen Engleman Conners.

The following investigative groups were formed during the course of this investigation: Structures, Systems, Powerplants, Air Traffic Control, Meteorology, Operations, Human Performance, Airport/Survival Factors, Airplane Performance, Flight Data Recorder, and Cockpit Voice Recorder.

Parties to the investigation were the Federal Aviation Administration (FAA); Boeing Commercial Airplane Company; Southwest Airlines, Inc. (SWA); Southwest Airlines Pilots Association (SWAPA); National Air Traffic Controllers Association (NATCA); the City of Chicago; CFM International; SWA Employee Association Dispatch; Transport Workers Union #556; and SWA AMFA. The Safety Board received submissions on this accident from SWA, SWAPA, Boeing, and the City of Chicago.

Public Hearing

A public hearing was held on June 21 and 22, 2006, in Washington, D.C. Then-Acting Chairman Mark V. Rosenker presided over the hearing.

The issues discussed at the public hearing were the accuracy and dissemination of runway friction measurements, the adequacy of runway safety areas on the ends of runways, and aircraft landing performance. Parties to the public hearing were the FAA, SWA, SWAPA, Boeing Commercial Airplane Company, and the City of Chicago.

AIRCRAFTAccident Report

APPENDIX B

Cockpit Voice Recorder

The following is a transcript of the Honeywell model 6022 cockpit voice recorder installed on Southwest Airlines flight 1248, a Boeing 737-74H, N471WN, which ran off the departure end of runway 31C after landing at Chicago Midway International Airport, Chicago, Illinois, on December 8, 2005.

LEGEND

CAM Cuckpit area microphone voice or sound source

CTR Transmission from FAA Carrier controller

EXECUB2 Transmission from Exec Jet 202

GZKF Transmission from landing aircraft G3KF

HOT Crewmember hot microphone voice or sound sound

NAV Signal from ground-based navigational aid

OPS Transmission Company operations center at Highway airport.

RDO Radio transmission from N471WN

9M1952 Transmission from Southwest Airlines Right 1H02

TWR Transmission from Highway lower

-1 Voica identified as the captain

-2 Vokon identified as the first officer

-? Vokon unidentified

• Uninkelligible wird

• Explive

Propar nama

( ) Questionable insertion

... Pausa

• Vokou cutoff

Note 1: All times are Central Standard Time (CST).

Note 2: Words shown with excuse vowels, letters, or dream out syllable are a phonetic representation of the words as spoken.

Note 3: A non-permanent word or phrase, where noted, refers to a word or phrase not directly related to the operation, control or condition of the alarm.

Note 4: Only radio transmissions to and from the accident account were transcribed.

Appendix B

AIRCRAFT Accident Report

Appendix B

AIRCRAFT Accident Report

Appendix B

AIRCRAFTAccident Report

Appendix B Accident Report

FT

Appendix B

AIRCRAFTAccident Report

National Transportation Safety Board

77

INTRA-COCKPIT COMMUNICATION

AIR-GROUND COMMUNICATION

TIME (CST)SOURCE

CONTENT

TIME (CST)SOURCE

CONTENT

and folks good evenin' ah again from the guys up front thank you so much for your patience this evenin' ah with our troubles with mother nature we sure do appreciate your understanding are at thirty nine thousand feet we're gonna make a slow climb to forty thousand feet here in just a couple minutes our friends at air traffic controller (tell) us its gonna be a pretty smooth flight this evenin' [sound similar to seatbelt warning tone] the seatbelt signs comin' off so folks if you wanna get up and stretch your legs or move about you sure can do so well please folks while you're in your seats always stay buckled up just in case we do find a few unexpected bumps along the way. ah folks as long as the flight attendants are busy trying to get their service out you sure can do them a big favor by trying to keep those aisles clear they really do appreciate it and so do we no lines up by the forward lavatory and you can't stand up in the forward galley area ah these are FAA security regulations and each of us want to thank you here in advance for complying'. ahhh pretty strong headwinds right now folks are out of the West at about a hundred and fifty knots 'bout a hundred seventy five mile an hour right on the nose ah normal a normally our speed across the ground is close to about five hundred miles an hour right now it's only about three hundred and fifty or so so it's not gonna help us make up any time at all right now about four hundred and fifty miles to go. showin' us ah - touchin' down in Chicago at about and hour twenty minutes or so 'bout an hour twenty five minutes we should have you safely at the gate, folks as we get closer * we'll keep you posted get you up to date on the latest for the Chicago weather. for now folks again ah thanks so much for your patience and understanding this evening we really do appreciate it and finally folks one extra note ah we have three great flight attendants and I promise ya they didn't have a single thing to do with us gettin' off to the late start this evenin' so folks please be kind to them 'cause they're gonna take excellent care of you thanks so much folks again and good evenin'.

Appendix B

AIRCRAFT Accident Report

Appendix B

AIRCRAFT Accident Report

Appendix B

AIRCRAFT Accident Report

National Transportation Safety Board

8

INTRA-COCKPIT COMMUNICATION

AIR-GROUND COMMUNICATION

Appendix B

AIRCRAFT Accident Report

Appendix B AIRCRAFT Accident Report

F1

Appendix B

AIRCRAFTAccident Report

Appendix B AIRCRAFT Accident Report

Appendix B

AIRCRAFT Accident Report

Appendix B AIRCRAFT Accident Report

Appendix B

AIRCRAFTAccident Report

References

References

17:37:32.9

HOT-1 says it's a requirement.

References

References

References

References

References

17:39:55.9 HOT-2 maybe there is once we get in here there might be something further down the road that.

References

CAM-1 we haven't had it that long. 17:40:49.9 CAM-2 no.

17:41:06.9

HOT-1 where's that sucker . 17:41:11.5

HOT-2 I'm hoping that in the like the normal.

17:41:14.5 CAM-2 or in the approach it might have some guidance on it. 17:41:21.9

HOT-1 zero eight zero at ten. huh.

References

References

References

17:43:00.4 HOT-2 zero eight zero at ten, must be right on the limit.

References

References

References

References

References

References

References

17:50:07.1 HOT-2 okay. 17:50:07.9

HOT-1 since we're gettin' in that area. 17:50:28.7

PA-1 ah flight attendants go ahead and take your seats for a few minutes as well. folks I've asked the flight attendants to take their seats so ah make sure that you're in your seats as well seatbelts fastened thank you.

17:50:39.4 CAM-2 (yeah).

References

References

References

References

References

References

17:54:43.1 HOT-2 here's some completely useless knowledge for ya.

this is great when you have two alternates.

References

References

References

References

References

References

References

References

References

References

References

HOT-1 be where ya gotta be.

18:03:28.5 CAM-1 I picked it up for a guy so he could be home with his three year old and ah six year old.

18:03:33.3 CAM-2 aren't you a nice guy.

18:03:35.9 CAM-2 where ya gonna be.

References

References

References

References

18:08:00.9 CAM-1 #.

18:08:02.9 CAM-2 we gotta check if it's fair.

References

References

References

References

References

18:10:55.9 CAM-? * one thousand (three). 18:11:02.4 CAM-1 one oh nine nine three fifteen inbound seventeen hundred at HOBEL that's (ten ten) eighty seven.

18:11:07.9

HOT-1 eight seventeen the decision height two hundred we'll keep in the radar altimeter.

References

18:11:35.3 RDO-2 okay where's everybody holdin '? 18:11:39.3 CAM-1 (alright) we'll slow 'er down.

18:11:43.4

HOT-1 so anyway six thirteen touchdown ah we got the minsafes there they're at twenty eight and thirty four north.

18:11:50.0

HOT-1 ahmm.

18:11:53.0

HOT-1 we got all those special aircrew certification required we got that ah lead in REILs VASIs HIRLs RVR three one center must be operating and DME required. ahmm need three thousand RVR three degree glideslope. if we have to go missed approach it's climb to eleven hundred feet then ah climbing left turn to twenty one via heading one five zero * the PEON VOR zero zero one until crossing the IGECY. 18:12:31.9

HOT-1 -intersection then climb to twenty six. fracken a.

References

References

References

18:13:56.6

CAM-1 two eight zero.

18:13:57.7 CAM-2 okay.

18:13:58.0 CAM-1 here we go.

18:14:11.2 CAM-2 ah we have this missed in here? ah three one center eleven hundred one fifty IGECY * .

18:14:19.7

HOT-1 and all the altitudes in there good.

18:14:21.5

HOT-2 ahhh what's the eight seventeen. we need three thousand. or five (eighths). okay. that's good enough for me.

18:14:40.5

HOT-1 I'll hold around two twenty does that sound good to you?

18:14:42.8

HOT-2 sure.

18:14:43.1

HOT-1 you know actually I don't need this anymore.

18:14:44.9

HOT-2 you don't need it?

18:14:46.1 HOT-1 I don't believe so.

References

References

References

References

References

References

References

References

18:18:33.0 RDO-2 okay great three fifty heading and two ten Southwest twelve forty eight.

References

References

Appendix B

National Transportation Safety Board

A I R C R A F T Accident Report

147

References

References

References

References

References

References

References

18:24:06.9

CAM-1 okay sir we're goin' down to one six thousand.

References

References

References

References

18:27:27.5 HOT-1 haven't gotten any on the outside on the very eh outer edge do we?

18:27:31.4

HOT-2 ah vee looks like ah on top --18:27:33.9

HOT-1 I mean we have it there but we don't have any antiice on there.

References

References

References

References

References

References

References

References

References

Abstract

INTRA-COCKPIT COMMUNICATION AIR-GROUND COMMUNICATION TIME (CST) SOURCE CONTENT TIME (CST) SOURCE CONTENT DCA06MA009 CVR Group Chairman's Factual Report Attachment II -Transcript -Page 97 18:33:17.1 CTR Midway altimeter (three) zero zero and I have holding instructions advise when you're able to copy.

References

References

References

References

References

References

18:37:24.0 PA-1 well folks you've probably felt that ah we've slowed here ahm we're gonna have to hold here for about ah twenty minutes it looks like ah 'till they clear the runway off they've been off and on doing that ah as we've been flying into Chicago to get the braking action ah such that we can land. so ah it's still snowing so ah the plows are workin' on the runway we're gonna hold and let 'em do their job and then ah and then ah once they ah get then we'll be heading into Chicago so they gave us a fifty five after the hour expected approach clearance time and ah that's when we expect to ah leave the holding pattern and head to (Chicago) *. 18:38:28.9

HOT-1 * ETA zero zero four three eh? alright then we'll have about ah twelve minutes in the fix eleven twelve. ten thousand feet.

References

18:38:42.0 HOT-2 we got a lot a extra gas so that's not.

References

References

References

References

References

18:42:47.0 HOT-2 well let's do this wa how many we don't really have two much time forty three.

18:42:49.9

HOT-1 ah let's just enter here.

References

References

References

References

References

18:47:01.9

HOT-1 here we go. HOT-2 we're in a three hundred it wouldn't be so awesome.

References

References

References

References

18:51:00.9

HOT-2 some of my favorite people had to go and it was too bad $ he was * awesome guy to fly with outta Chicago.

18:51:07.6

HOT-2 I flew ah with $ his second to last night. 18:51:11.9

HOT-1 is that right?

References

References

18:51:56.4 PA ah folks just to give you a fast update we are estimating one more turn in the hold they're accepting aircraft back in ah Chicago Midway right now I think we're about three or four in the stack so hopefully we'll be heading that way as soon as we are we'll get back to ya but in the meantime folks thanks so much for your patience and hopefully we'll have you headin' towards the airport here in just a couple a minutes thanks.

18:52:18.6

HOT-1 well eighteen thirty's goin'.

18:52:21.9

HOT-2 yea and there is one more behind them and eh I thought they're at six the guys in front of us but.

18:52:26.4

HOT-1 yeah.

18:52:33.0 HOT-1 the other two seven zero.

18:52:34.7

HOT-2 yeah they're heading back up.

18:52:46.1 HOT-2 it's good that they're plowin'.

18:52:58.9

HOT-1

Uniform.

18:53:00.5

HOT-2 yeah that's another new one.

References

References

18:53:49.0 HOT-2 at three quarters I could probably undo the RVR less than four thousand. we'll leave it in just in case.

18:53:53.1

HOT-1 ahhhh well leave it in for now yeah that's the worst case.

18:54:02.6

HOT-1 well yeah.

References

References

References

References

References

18:57:51.5

HOT-1 right cross so. comin' like this so I'll be lookin out this way here. little bit *.

18:57:57.4

HOT-2 yeah.

18:58:05.7

HOT-1 we'll be kinda doin' HUD. * doin' it on the HUD.

once we get down there.

18:58:09.9

HOT-2 yeah HGS.

18:58:14.6

HOT-2 whatta we got six?

References

References

18:59:00.2 CAM-1

Hmmum.

18:59:05.6 CAM-2 so it'll be nineteen *.

References

References

19:00:30.5 CAM-2 yea.

19:00:30.7 CAM-1 they can think that far ahead today. 19:00:52.6

HOT-1 zero tree zero here we go.

19:00:54.5

HOT-2 yeah V-P-Z Valperazo.

19:01:11.7

HOT-1 he might take us through uh.

19:01:13.4

HOT-2 yea I'm going to hard altitude these.

19:01:15.9 CTR Southwest twelve forty eight descend and maintain six thousand.

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

References

Appendix B

National Transportation Safety Board

A I R C R A F T Accident Report

224

National Transportation Safety Board

A I R C R A F T Accident Report

225

Appendix C

FAA sAFety Alert For operAtors 06012

Approved by AFS-1

Page 1

SAFO

Safety Alert for Operators

U.S. Department

SAFO 06012

of Transportation

DATE: 8/31/06

Federal Aviation Administration

Flight Standards Service Washington, DC

http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo

A SAFO contains important safety information and may include recommended action. SAFO content should be

especially valuable to air carriers in meeting their statutory duty to provide service with the highest possible degree of safety in the public interest.

Subject: Landing Performance Assessments at Time of Arrival (Turbojets)

1. Purpose. This SAFO urgently recommends that operators of turbojet airplanes develop

procedures for flightcrews to assess landing performance based on conditions actually existing at time of arrival, as distinct from conditions presumed at time of dispatch. Those conditions

include weather, runway conditions, the airplane’s weight, and braking systems to be used. Once the actual landing distance is determined an additional safety margin of at least 15% should be

added to that distance. Except under emergency conditions flightcrews should not attempt to

land on runways that do not meet the assessment criteria and safety margins as specified in this SAFO.

1. Discussion: This SAFO is based on the FAA’s policy statement published in the Federal

Register on June 7, 2006, and incorporates revisions based on public comments received by the FAA. Accordingly, the FAA has undertaken rulemaking that would explicitly require the

practice described above. Operators may use Operation/Management Specification paragraph

C382 to record their voluntary commitment to this practice, pending rulemaking.

Operators engaged in air transportation have a statutory obligation to operate with the highest possible degree of safety in the public interest.

1. Applicability:

a. This SAFO applies to all turbojet operators under Title 14 of the Code of Federal

Regulations (14 CFR) parts 121, 135, 125, and 91 subpart K. The intent of providing this

information is to assist operators in developing methods of ensuring that sufficient landing

distance exists to safely make a full stop landing with an acceptable safety margin on the runway to be used, in the conditions existing at the time of arrival, and with the deceleration means and airplane configuration that will be used. The FAA considers a 15% margin between the expected actual airplane landing distance and the landing distance available at the time of arrival as the

minimum acceptable safety margin for normal operations.

b. The FAA acknowledges that there are situations where the flightcrew needs to know the absolute performance capability of the airplane. These situations include emergencies or

abnormal and irregular configurations of the airplane such as engine failure or flight control

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

226

Approved by AFS-1

Page 2

malfunctions. In these circumstances, the pilot must consider whether it is safer to remain in the air or to land immediately and must know the actual landing performance capability (without an added safety margin) when making these evaluations. This guidance is not intended to curtail

such evaluations from being made for these situations.

c. This guidance is independent of the preflight landing distance planning requirements of

part 121, section 121.195, part 135, section 135.385, and part 91, section 91.1037.

d. This 15% safety margin should not be applied to the landing distance determined for

compliance with any other OpSpec/MSpec requirement. The landing distance assessment of this guidance is independent of any other OpSpec/MSpec landing distance requirement. The

minimum landing distance should comply with all applicable landing distance requirements.

Hence, the minimum landing distance at the time of arrival should be the longer of the landing

distance in this guidance and that determined to be in compliance with any other applicable

OpSpec/MSpec.

e. This guidance does not apply to Land and Hold Short Operations (LAHSO).

1. Definitions: The following definitions are specific to this guidance and may differ with those definitions contained in other published references.

a. Actual Landing Distance. The landing distance for the reported meteorological and

runway surface conditions, runway slope, airplane weight, airplane configuration, approach

speed, use of autoland or a Head-up Guidance System, and ground deceleration devices planned to be used for the landing. It does not include any safety margin and represents the best

performance the airplane is capable of for the conditions.

b. Airplane Ground Deceleration Devices. Any device used to aid in the onset or rate of airplane deceleration on the ground during the landing roll out. These would include, but not be limited to: brakes (either manual braking or the use of autobrakes), spoilers, and thrust reversers. c. At Time of Arrival. For the purpose of this guidance means a point in time as close to

the airport as possible consistent with the ability to obtain the most current meteorological and

runway surface conditions considering pilot workload and traffic surveillance, but no later than the commencement of the approach procedures or visual approach pattern.

d. Braking Action Reports. The following braking action reports are widely used in the

aviation industry and are furnished by air traffic controllers when available. The definitions

provided below are consistent with how these terms are used in this guidance.

Good – More braking capability is available than is used in typical deceleration on a nonlimiting runway (i.e., a runway with additional stopping distance available). However, the landing distance will be longer than the certified (unfactored) dry runway landing

distance, even with a well executed landing and maximum effort braking.

Fair/Medium – Noticeably degraded braking conditions. Expect and plan for a longer

stopping distance such as might be expected on a packed or compacted snow-covered

runway.

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

227

Approved by AFS-1

Page 3

Poor – Very degraded braking conditions with a potential for hydroplaning. Expect and plan for a significantly longer stopping distance such as might be expected on an icecovered runway.

Nil – No braking action and poor directional control can be expected.

NOTE: Conditions specified as “nil” braking action are not considered safe,

therefore operations under conditions specified as such should not be

conducted. Do not attempt to operate on surfaces reported or expected to

have nil braking action.

e. Factored Landing Distance. The landing distance required by 14 CFR part 25, section

1. 125 increased by the preflight planning safety margin additives required by the applicable

operating rules. (Some manufacturers supply factored landing distance information in the

Airplane Flight Manual (AFM) as a service to the user.)

f. Landing Distance Available. The length of the runway declared available for landing.

This distance may be shorter than the full length of the runway.

g. Meteorological Conditions. Any meteorological condition that may affect either the air or ground portions of the landing distance. Examples may include wind direction and velocity, pressure altitude, and temperature. An example of a possible effect that must be considered

includes crosswinds affecting the amount of reverse thrust that can be used on airplanes with tail mounted engines due to rudder blanking effects.

h. Reliable Braking Action Report. For the purpose of this guidance, means a braking

action report submitted from a turbojet airplane with landing performance capabilities similar to those of the airplane being operated.

i. Runway Surface Conditions. The state of the surface of the runway: either dry, wet, or contaminated. A dry runway is one that is clear of contaminants and visible moisture within the required length and the width being used. A wet runway is one that is neither dry nor

contaminated. For a contaminated runway, the runway surface conditions include the type and depth (if applicable) of the substance on the runway surface, e.g., standing water, dry snow, wet snow, slush, ice, sanded, or chemically treated.

j. Runway Friction or Runway Friction Coefficient. The resistance to movement of an

object moving on the runway surface as measured by a runway friction measuring device. The resistive force resulting from the runway friction coefficient is the product of the runway friction coefficient and the weight of the object.

k. Runway Friction Enhancing Substance. Any substance that increases the runway

friction value.

l. Safety Margin. The length of runway available beyond the actual landing distance.

Safety margin can be expressed in a fixed distance increment or a percentage increase beyond

the actual landing distance required.

m. Unfactored Certified Landing Distance. The landing distance required by

section 25.125 without any safety margin additives. The unfactored certified landing distance

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

228

Approved by AFS-1

Page 4

may be different from the actual landing distance because not all factors affecting landing

distance are required to be accounted for by section 25.125. For example, the unfactored

certified landing distances are based on a dry, level (zero slope) runway at standard day

temperatures, and do not take into account the use of autobrakes, autoland systems, head-up

guidance systems, or thrust reversers.

1. Background: After any serious aircraft accident or incident, the FAA typically performs an internal audit to evaluate the adequacy of current regulations and guidance information in areas that come under scrutiny during the course of the accident investigation. The Southwest Airlines landing overrun accident involving a Boeing 737-700 at Chicago Midway Airport in December 2005 initiated such an audit. The types of information that were evaluated in addition to the

regulations were FAA orders, notices, advisory circulars, ICAO and foreign country

requirements, airplane manufacturer-developed material, independent source material, and the

current practices of air carrier operators. This internal FAA review revealed the following

issues:

a. A survey of operators’ manuals indicated that approximately fifty percent of the operators surveyed do not have policies in place for assessing whether sufficient landing distance exists at the time of arrival, even when conditions (including runway, meteorological, surface, airplane

weight, airplane configuration, and planned usage of decelerating devices) are different and

worse than those planned at the time the flight was released.

b. Not all operators who perform landing distance assessments at the time of arrival have

procedures that account for runway surface conditions or reduced braking action reports.

c. Many operators who perform landing distance assessments at the time of arrival do not

apply a safety margin to the expected actual landing distance. Those that do are inconsistent in applying an increasing safety margin as the expected actual landing distance increased (i.e., as a percentage of the expected actual landing distance).

d. Some operators have developed their own contaminated runway landing performance data or are using data developed by third party vendors. In some cases, these data indicate shorter

landing distances than the airplane manufacturer’s data for the same conditions. In other cases,

an autobrake landing distance chart has been misused to generate landing performance data for

contaminated runway conditions. Also, some operators’ data have not been kept up to date with the manufacturer’s current data.

e. Credit for the use of thrust reversers in the landing performance data is not uniformly

applied and pilots may be unaware of these differences. In one case, there were differences

found within the same operator from one series of airplane to another within the same make and model. The operator’s understanding of the data with respect to reverse thrust credit, and the

information conveyed to pilots, were both incorrect.

f. Airplane flight manual (AFM) landing performance data are determined during flighttesting using flight test and analysis criteria that are not representative of everyday operational

practices. Landing distances determined in compliance with 14 CFR part 25, section 25.125 and published in the FAA-approved AFM do not reflect operational landing distances (Note: some

manufacturers provide factored landing distance data that addresses operational requirements.) Landing distances determined during certification tests are aimed at demonstrating the shortest

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

229

Approved by AFS-1

Page 5

landing distances for a given airplane weight with a test pilot at the controls and are established with full awareness that operational rules for normal operations require additional factors to be added for determining minimum operational field lengths. Flight test and data analysis

techniques for determining landing distances can result in the use of high touchdown sink rates (as high as 8 feet per second) and approach angles of -3.5 degrees to minimize the airborne

portion of the landing distance. Maximum manual braking, initiated as soon as possible after

landing, is used in order to minimize the braking portion of the landing distance. Therefore, the landing distances determined under section 25.125 are shorter than the landing distances

achieved in normal operations.

g. Wet and contaminated runway landing distance data are usually an analytical computation using the dry, smooth, hard surface runway data collected during certification. Therefore, the wet and contaminated runway data may not represent performance that would be achieved in normal operations. This lack of operational landing performance repeatability from the flight test data,

along with many other variables affecting landing distance, are taken into consideration in the

preflight landing performance calculations by requiring a significant safety margin in excess of the certified (unfactored) landing distance that would be required under those conditions.

However, the regulations do not specify a particular safety margin for a landing distance

assessment at the time of arrival. This safety margin has been left largely to the operator and/or the flightcrew to determine.

h. Manufacturers do not provide advisory landing distance information in a standardized

manner. However, most turbojet manufacturers make landing distance performance information available for a range of runway or braking action conditions using various airplane deceleration devices and settings under a variety of meteorological conditions. This information is made

available in a wide variety of informational documents, dependent upon the manufacturer.

i. Manufacturer-supplied landing performance data for conditions worse than a dry, smooth runway is normally an analytical computation based on the dry runway landing performance

data, adjusted for a reduced airplane braking coefficient of friction available for the specific

runway surface condition. Most of the data for runways contaminated by snow, slush, standing water, or ice were developed to show compliance with European Aviation Safety Agency and

Joint Aviation Authority airworthiness certification and operating requirements. The FAA

considers the data developed for showing compliance with the European contaminated runway certification or operating requirements, as applicable, to be acceptable for making landing

distance assessments for contaminated runways at the time of arrival.

1. Recommended Action:

a. A review of the current applicable regulations indicates that the regulations do not specify the type of landing distance assessment that must be performed at the time of arrival, but

operators are required to restrict or suspend operations when conditions are hazardous.

b. 14 CFR part 121, section 121.195(b), part 135, section 135.385(b), and part 91, section

1. 1037(b) and (c) require operators to comply with certain landing distance requirements at the time of takeoff. (14 CFR part 125, section 125.49 requires operators to use airports that are

adequate for the proposed operation). These requirements limit the allowable takeoff weight to that which would allow the airplane to land within a specified percentage of the landing distance available on: (1) the most favorable runway at the destination airport under still air conditions;

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

230

Approved by AFS-1

Page 6

and (2) the most suitable runway in the expected wind conditions. Sections 121.195(d),

1. 385(d), and 91.1037(e) further require an additional 15 percent to be added to the landing

distance required when the runway is wet or slippery, unless a shorter distance can be shown

using operational landing techniques on wet runways. Although an airplane can be legally

dispatched under these conditions, compliance with these requirements alone does not ensure

that the airplane can safely land within the distance available on the runway actually used for

landing in the conditions that exist at the time of arrival, particularly if the runway, runway

surface condition, meteorological conditions, airplane configuration, airplane weight, or use of

airplane ground deceleration devices is different than that used in the preflight calculation. Part 121, sections 121.533, 121.535, 121.537, part 135, section 135.77, part 125, section 125.351, and part 91, sections 91.3, and 91.1009 place the responsibility for the safe operation of the flight

jointly with the operator, pilot in command, and dispatcher as appropriate to the type of

operation being conducted.

c. Sections 121.195(e) and 135.385(e), allow an airplane to depart even when it is unable to comply with the conditions referred to in item (2) of paragraph 5b above if an alternate airport is specified where the airplane can comply with conditions referred to in items (1) and (2) of

paragraph 5b. This implies that a landing distance assessment is accomplished before landing to determine if it is safe to land at the destination, or if a diversion to an alternate airport is required. d. Part 121, sections 121.601 and 121.603, require dispatchers to keep pilots informed, or for pilots to stay informed as applicable, of conditions, such as airport and meteorological

conditions, that may affect the safety of the flight. Thus, the operator and flightcrew use this

information in their safety of flight decision making. Part 121, sections 121.551, 121.553, and

part 135, section 135.69, require an operator, and/or the pilot in command as applicable, to

restrict or suspend operations to an airport if the conditions, including airport or runway surface conditions, are hazardous to safe operations. Part 125 section 125.371 prohibits a pilot in

command (PIC) from continuing toward any airport to which it was released unless the flight can be completed safely. A landing distance assessment should be made under the conditions

existing at the time of arrival in order to support a determination of whether conditions exist that may affect the safety of the flight and whether operations should be restricted or suspended.

e. Runway surface conditions may be reported using several types of descriptive terms

including: type and depth of contamination, a reading from a runway friction measuring device, an airplane braking action report, or an airport vehicle braking condition report. Unfortunately, joint industry and multi-national government tests have not established a reliable correlation

between runway friction under varying conditions, type of runway contaminants, braking action reports, and airplane braking capability. Extensive testing has been conducted in an effort to find a direct correlation between runway friction measurement device readings and airplane braking friction capability. However, these tests have not produced conclusive results that indicate a

repeatable correlation exists through the full spectrum of runway contaminant conditions.

Therefore, operators and flightcrews cannot base the calculation of landing distance solely on

runway friction meter readings. Likewise, because pilot braking action reports are subjective,

flightcrews must use sound judgment in using them to predict the stopping capability of their

airplane. For example, the pilots of two identical aircraft landing in the same conditions, on the same runway could give different braking action reports. These differing reports could be the

result of differences between the specific aircraft, aircraft weight, pilot technique, pilot

experience in similar conditions, pilot total experience, and pilot expectations. Also, runway

surface conditions can degrade or improve significantly in very short periods of time dependent

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

231

Approved by AFS-1

Page 7

on precipitation, temperature, usage, and runway treatment and could be significantly different

than indicated by the last report. Flightcrews must consider all available information, including runway surface condition reports, braking action reports, and friction measurements.

(1) Operators and pilots should use the most adverse reliable braking action report, if

available, or the most adverse expected conditions for the runway, or portion of the runway, that will be used for landing when assessing the required landing distance prior to landing. Operators and pilots should consider the following factors in determining the actual landing distance: the

age of the report, meteorological conditions present since the report was issued, type of airplane or device used to obtain the report, whether the runway surface was treated since the report, and the methods used for that treatment. Operators and pilots are expected to use sound judgment in determining the applicability of this information to their airplane’s landing performance.

(2) Table 1 provides an example of a correlation between braking action reports and

runway surface conditions:

Braking

Action

Dry (not reported)

Good Fair/Medium

Poor

Nil

Contaminant Dry

Wet

Dry Snow (< 20mm)

Packed or Compacted Snow

Wet Snow

Slush

Standing Water Ice

Wet ice

Table 1. Relationship between braking action reports and runway surface condition

(contaminant type)

NOTE: Under extremely cold temperatures, these relationships may be less

reliable and braking capabilities may be better than represented. This table

does not include any information pertaining to a runway that has been

chemically treated or where a runway friction enhancing substance has been

applied.

f. Some advisory landing distance information uses a standard air distance of 1000 feet from 50 feet above the runway threshold to the touchdown point. Unfactored dry runway landing

distances in AFMs reflect the distances demonstrated during certification flight testing. These unfactored AFM landing distance data include air distances that vary with airplane weight, but are also nominally around 1000 feet. A 1000 foot air distance is not consistently achievable in normal flight operations. Additionally, the use of automatic landing systems (autoland) and

other landing guidance systems (e.g., head-up guidance systems) typically result in longer air

distances. Operators are expected to apply adjustments to this air distances to reflect their

specific operations, operational practices, procedures, training, and experience.

g. To ensure that an acceptable landing distance safety margin exists at the time of arrival, the FAA recommends that at least a 15% safety margin be provided. This safety margin

represents the minimum distance margin that must exist between the expected actual landing

distance at the time of arrival and the landing distance available, considering the meteorological and runway surface conditions, airplane configuration and weight, and the intended use of

airplane ground deceleration devices. In other words, the landing distance available on the

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

232

Approved by AFS-1

Page 8

runway to be used for landing must allow a full stop landing, in the actual conditions and

airplane configuration at the time of landing, and at least an additional 15% safety margin.

h. Operator compliance can be accomplished by a variety of methods and procedurally

should be accomplished by the method that best suits the operator’s current procedures. The

operator’s procedures should be clearly articulated in the operations manual system for affected personnel. The following list of methods is not all inclusive, or an endorsement of any particular methods, but provided as only some examples of methods of compliance.

• Establishment of a minimum runway length required under the worst case meteorological and runway surface conditions for operator’s total fleet or fleet type that will provide

runway lengths that comply with this guidance.

• The requirements of this paragraph could be considered along with the other applicable preflight landing distance calculation requirements and the takeoff weight adjusted to

provide for compliance at the time of arrival under the conditions and configurations

factored in the calculation. This information, including the conditions/configurations/etc. used in the calculation, would be provided to the flightcrew as part of the release/dispatch documents. (However, this method may not be sufficient if

conditions/configurations/etc. at the time of arrival are different than those taken into

account in the preflight calculations; therefore, the flightcrew would need to have access to the landing performance data applicable to the conditions present upon arrival.

• Tab or graphical data accounting for the applicable variables provided to the flightcrew and/or dispatcher as appropriate to the operator’s procedures.

• Electronic Flight Bag equipment that has methods for accounting for the appropriate

variables.

NOTE: These are only some examples of methods of compliance. There are

many others that would be acceptable.

1. Summary of Recommendation.

a. Turbojet operators have procedures to ensure that a full stop landing, with at least a 15% safety margin beyond the actual landing distance, can be made on the runway to be used, in the conditions existing at the time of arrival, and with the deceleration means and airplane

configuration that will be used. This assessment should take into account the meteorological

conditions affecting landing performance (airport pressure altitude, wind velocity, wind

direction, etc.), surface condition of the runway to be used for landing, the approach speed,

airplane weight and configuration, and planned use of airplane ground deceleration devices. The airborne portion of the actual landing distance (distance from runway threshold to touchdown

point) should reflect the operator’s specific operations, operational practices, procedures,

training, and experience. Operators should have procedures for compliance with this guidance,

absent an emergency, after the flightcrew makes this assessment using the air carrier’s

procedures, if at least the 15% safety margin is not available, the pilot should not land the

aircraft.

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

233

Approved by AFS-1

Page 9

(1) This assessment does not mean that a specific calculation must be made before every

landing. In many cases, the before takeoff criteria, with their large safety margins, will be

adequate to ensure that there is sufficient landing distance with at least a 15% safety margin at

the time of arrival. Only when the conditions at the destination airport deteriorate while en route (e.g., runway surface condition, runway to be used, winds, airplane landing

weight/configuration/speed/deceleration devices) or the takeoff was conducted under the

provisions described in paragraph 5 (c) of this guidance, would a calculation or other method of determining the actual landing distance capability normally be needed. The operator should

develop procedures to determine when such a calculation or other method of determining the

expected actual landing distance is necessary to ensure that at least a 15% safety margin will

exist at the time of arrival.

(2) Operators may require flight crews to perform this assessment, or may establish other procedures to conduct this assessment. Whatever method(s) the operator develops, its procedures should account for all factors upon which the preflight planning was based and the actual

conditions existing at time of arrival.

b. Confirm that the procedures and data used to comply with paragraph 6 (a) above for

actual landing performance assessments yield results that are at least as conservative as the

manufacturer’s approved or advisory information for the associated conditions provided therein.

Although the European contaminated runway operations requirements are applied differently

than the requirements of this guidance, the operator may choose to use data developed for

showing compliance with the European contaminated runway operating requirements for making these landing distance assessments for contaminated runways at the time of arrival.

c. A safety margin of 15% should be added to the actual landing distance and require that the resulting distance be within the landing distance available of the runway used for landing. Note that the FAA considers a 15% margin to be the minimum acceptable safety margin.

d. If wet or contaminated runway landing distance data are unavailable, the factors in Table 2 should be applied to the pre-flight planning (factored) dry runway landing distances

determined in accordance with the applicable operating rule (e.g., sections 91.1037, 121.195(b) or 135.385(b). Table 2 should only apply when no such data are available. The factors in Table 2 include the 15% safety margin recommended by this guidance, and are considered to include

an air distance representative of normal operational practices. Therefore, operators do not need to apply further adjustments to the resulting distances to comply with the recommendations of

this guidance.

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

234

Approved by AFS-1

Page 10

Runway Condition

Reported Braking

Action

Factor to apply to

(factored) dry runway landing distance*

Wet Runway, Dry Snow

Good

1. 9

Packed or Compacted Snow

Fair/Medium

1. 2

Wet snow, slush, standing water, ice

Poor

1. 6

Wet ice

Nil

Landing is prohibited

Table 2. Multiplication factors to apply to the factored dry runway landing distances when the data for the specified runway condition are unavailable.

• The factored dry runway landing distances for use with Table 2 must be based on landing

within a distance of 60% of the effective length of the runway, even for operations where the

preflight planning (factored) dry runway landing distances are based on landing within a distance other than 60% of the effective length of the runway (e.g., certain operations under part 135 and subpart K of par t91). To use unfactored dry runway landing distances, first multiply the

unfactored dry runway landing distance by 1.667 to get the factored dry runway landing distance before entering Table 2 above.

NOTE: These factors assume maximum manual braking, autospoilers (if so

equipped), and reverse thrust will be used. For operations without reverse

thrust (or without credit for the use of reverse thrust) multiply the results of

the factors in Table 2 by 1.2. These factors cannot be used to assess landing

distance requirements with autobrakes.

e. The landing distance assessment should be accomplished as close to the time of arrival as practicable, taking into account workload considerations during critical phases of flight, using

the most up-to-date information available at that time. The most adverse braking condition,

based on reliable braking reports or runway contaminant reports (or expected runway surface

conditions if no reports are available) for the portion of the runway that will be used for the

landing should be used in the actual landing performance assessment. For example, if the runway surface condition is reported as fair to poor, or fair in the middle, but poor at the ends, the

runway surface condition should be assumed to be poor for the assessment of the actual landing distance. (This example assumes the entire runway will be used for the landing). If conditions change between the time that the assessment is made and the time of landing, the flightcrew

should consider whether it would be safer to continue the landing or reassess the landing

distance.

f. The operator’s flightcrew and dispatcher training programs should include elements that

provide knowledge in all aspects and assumptions used in landing distance performance

determinations. This training should emphasize the airplane ground deceleration devices,

settings, and piloting methods (e.g., air distance) used in determining landing distances for each make, model, and series of airplane. Elements such as braking action reports, airplane

configuration, optimal stopping performance techniques, stopping margin, the effects of excess speed, delays in activating deceleration devices, and other pilot performance techniques should be covered. All dispatchers and flightcrew members should be trained on these elements prior to operations on contaminated runway surfaces. This training should be accomplished in a manner consistent with the operator’s methods for conveying similar knowledge to flight operations

Appendix C

National Transportation Safety Board

A I R C R A F T Accident Report

235

Approved by AFS-1

Page 11

personnel. It may be conducted via operations/training bulletins or extended learning systems, if applicable to the operator’s current methods of training.

g. Procedures for obtaining optimal stopping performance on contaminated runways should be included in flight training programs. All flight crewmembers should be made aware of these procedures for the make/model/series of airplane they operate. This training should be

accomplished in a manner consistent with the operator’s methods for conveying similar

knowledge to flight operations personnel. It may be conducted via operations/training bulletins or extended learning systems, if applicable to the operator’s current methods of training. In

addition, if not already included, these procedures should be incorporated into each airplane or simulator training curriculum for initial qualification on the make/model/series airplane, or

differences training as appropriate. All flight crewmembers should have hands on training and validate proficiency in these procedures during their next flight training event, unless previously demonstrated with their current employer in that make/model/series of airplane.