1976_美国_AAR7617.pdf

8 U.S. DEPRINMENT OF COMMERCE National Technical Information Services

NTISUB/B/104-76/017

Mercer Airines, Inc., Douglas DC-6/YC-112A, N901MA Near Van Nuys Airport, Van Nuys, CA, Feb. 8, 1976

National Transportation Safety Board, Washington, D'C

18 Aug 76

TECHNICAL REPORT DOCUMENTATION PAGE.

15. Supplementary Notes:

1. Abstract At 1044 P.s.t. February 8, 1976, Mercer Airlines Flight 901 crashed while attempting an emergency landing on runway 34L at the Van Nuys Airpcrt, Van Nuys, California. The No. 3 engine had separated from the aircraft during takeoff from runway 15 at the Hollywood-Burbank Airport, Burbank, California; the No. 2 engine failed while en route from Burbank to Van Nuys. The aircraft crashed on a golf course about 1 mile short of the threshold of runway 34L at Van Nuys.

Of the six persons on board the aircraft, three flightcrew members were killed; two flight attendants and a nonrevenue company employee were injured slightly. One person on the ground was injured slightly. During a postaccident fire, ten firemen were burned; three, seriously. The aircraft was destroyed.

The National Transportation Safety Board determines that the probable cause of this accident was the degraded performance of the aircraft after two engines failed. The dual failure was precipitated by the in-flight failure of the No. 1 blade of the No. 3 propeller assembly. The failure of the propeller blade resulted from a fatigue crack which originated in the leading edge under the deler boot. The crack had not been detected during an improperly performed overhaul. ∠

Ac a result of its investigation of this accident, the Safety Board issued three recommendations to the Federal Aviation Administration.

NTSB Form 1765.2 (Rev. 9/74)

TABLE OF CONTENTS

NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. 20594

AIRCRAPT ACCIDENT REPORT

Adopted: August 18, 1976

MERCER AIALINES, INC. DOUGLAS DC-6/YC-112A, N901MA NEAR VAN NUYS, CALIFORNIA FEBRUARY 8, 1976

SYNOPSIS

At 1044 P.s.t. February 8, 1976, Mercer Airlines Flight 901 crashed while attempting an emergency landing on runway 34L at the Van Nuys Airport, Van Nuys, California. The No. 3 engine had separated from the aircraft during takeoff from runway 15 at the Hollywood-Burbank. Airport, Burbank, California; the No. 2 engine failed while en route from Burbank to Van Nuys. The aircraft crashed on a golf course about 1 mile short of the threshold of runway 34L at Van Nuys.

Of the six persons on board the aircraft, three flightcrew members were killed; two flight attendants and a nonrevenue company employee were injured slightly. One person on the ground was injured slightly. During a postaccident fire, ten firmen were burned; three, seriously. The aircraft was destroyed.

The National Transportation Safety Board determines that the probable cause of this accident was the degraded performance of the aircraft after two engines failed. The dual failure was precipitated by the in-flight failure of the No. 1 blade of the No. 3 propeller assembly. The failure of the propeller blade resulted from a fatigue crack which originated in the leading edge under the deicer boot. The crack had not been detected during an improperly p :formed overhaul.

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1. INVESTIGATION

1.1 History of the Flight

On February 8, 1976, Mercer Airlines Flight 901, a Douglas DC-6/YC-112A, (N901MA), was being ferried from Burbank, California, to Ontario, California. There were three flightcrew members, two cabin crewmembers, and one nonrevenue company employee on board the aircraft.

The cockpit voice recorded (CVR) transcript indicated that while the aircraft was taxing at the Hollywood-Burbank Airport, the crew discussed a problem with the fuel pressure and the boost pump on the No. 3 engine. The hydraulically operated windshield wipers had been turned on because of rain. Also, there was a comment recorded on CVP, "That one inverter sounds awful."

At 1035:00, 1/ Flight 901 was cleared by the Hollywood-Burbank Tower to make a rolling takeoff on runway 15. During acceleration, the flight engineer stated, "Look at that warning light on No. 3." There was no verbal response from any other crewmember. The aircraft was accelerated normally to $V_1$ and $V_2$, was rotated, and was lifted off without difficulty. Shortly after the captain called for gear and flaps up, a loud noise was heard and the flight engineer announced that they had lost the No. 3 engine. Ground witnesses eaw a flash of fire, black smoke, flying objects from the No. 3 engine, and the No. 3 engine separate from the aircraft. The first officer informed the captain that the engine had separated. The aircraft continued to climb and began a right turn.

At 1036:09, the crew of Flight 901 advised the Hollywood-Burbank Tower that they were returning to the airport and were declaring an emergency. They then requested and received clearance for a landing on runway 07.

At 1036:21, the local controller advised the flight that there was "trash" across the intersection of runways 07/25 and 15/23. The crew requested that crash equipment stand by, and the tower again advised them of debris across the intersection. The crew then inquired as to whether they could land on runway 07 or divert to the Van Nuys Airport. The local controller advised that there would be no problem with landing on runway 07 but that they might strike some of the debris on the intersection. During this period the reading of the emergency checklist was heard in the background. The captain elected to continue the approach and engine power was reduced to METO. 2/ Immediately after the power was reduced, the crew saw that the No. 2 propeller reverse light was illuminated. Though incomplete, the emergency checklist was discontinued at that time.

1. All times are Pacific standard time based on the 24-hour clock.

2/ Maximum except takeoff.

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The captain called Zor gear down and full flaps. As the approach continued, the first officer called out the airspeeds and, after reporting 115 kn, he said, "You got it made."

Ground witnesses reported that, as the aircraft circled the Hollywood-Burbank Airport, only the nose gear was extended. As the aircraft approached runway 07 for the emergency landing, witnesses reported that the main gear was also extended. The witnesses did not see the position of the flaps.

The aircraft touched down near the end of runway 07; the captain called for flap retraction and "gate." 3/ The engine sounds increased, and the first officer advised the captain that the propellers were not going into reverse and to use the brakes. As the engine sound decreased, the captain replied that nothing was happening. The first officer said, "Get your air--get your air." The captain replied, "I'm doing it!" Maximum power was then applied; the aircraft again took off, and cleared the blast fence at the end of the runway by approximately 30 feet. The captain called for gear and flaps up. The first officer advised that the flaps were up as he positioned the gear handle to "up." Ground witnesses saw the aircraft begin a slow, climbing turn to the right.

At 1039:35, the crew advised the Hollywood-Burbank Tower that they had no brakes and that they were proceeding to the Van Nuys A.rport, 6 mai to the west. The crew then saw that the No. 2 oil pressure was low and that there was no BMEP 4/4 indication. Attempts to feather the No. 2 propeller were not successful, and the No. 2 engine stopped with the propeller blades at a positive, low pitch angle.

Ground witnesses reported that as the aircraft was proceeding toward Van Nuys Airport, the main gear was extended. The crew requested the Hollywood-Burbank Tower to inform the Van Nuys Tower that the flight would need to land on runway 34 and to have the emergency equipment stand by. This request was relayed to Van Nuys by the Burbank coordinator over the land line between the two towers. The flight contacted the Van Nuys Tower and was cleared by the local controller to enter traffic on the east side of the airport for a leading on runway 16, which was the active runway. The crew again requested runway 34 with the added information, ". . . that's about all we're going to make."

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At 1043:22, the Van Nuys local controller cleared the flight to land on runway 34L, and the creer reported they had no brakes. As the aircraft approached the airport from the southeast, it was losing altitude and airspeed. The crew realized that they could not reach the airport and the captain commented that the windshield wipers were inoperative. The flight engineer explained that the windshield wipers did not work because the hydraulic system was inoperative. The throttles were retarded and a forced landing was attempted on the Woodley Municipal Golf Course, about 1-mile south of the Van Nuys Airport.

The aircraft touched down on its main landing gear and bounced three times. The nose of the aircraft struck a 24-inch-high concrete foundation of a partially constructed building. The aircraft came to rest against a house trailer parked nearby. A fire erupted about 20 minutes after the crash while firemen were engaged in rescue activities.

The accident occurred during daylight hours at 1044:25 on February 8, 1976. The geographic coordinates of the accident site are 34°11′N latitude and 118°29′W longitude.

1.2 Injuries to Persons

1.3 Damage to Aircraft

The aircraft was destroyed.

1.4 Other Damage

A partially constructed building and a house trailer at the golf course were destroyed. Fairways, greens, a tee, and a power line were damaged.

1.5 Crew Information

The crew of Flight 901 was certified and trained in accordance with current FAA regulations. (See Appendix B.)

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1.6 Aircraft Information

1.6.1 $\blacktriangle$ Ircraft

The aircraft was certified in accordance with existing regulations. All maintenance checks and airworthiness directives had been performed as required. The most recent heavy maintenance check was accomplished by Mercer Airlines on December 13, 1975; total aircraft time was 10,226 hours. Total time of the aircraft at the time of the accident was 10,280.4 hours. (See Appendix C.)

At takeoff, the aircraft's gross weight was 64,579 lbs., including 9,600 lbs. of 100/130 octane aviation fuel. The center of gravity (c.g.) forward limit (landing gear extended) was 14 percent MAC, and the rear forward limit (landing gear extended) was 35 percent MAC. The weight and c.g. for the flight were within prescribed limits.

1.6.2 Propellers

The propellers installed on N901MA were Curtiss-Wright electric propellers, type C632-S. Propeller No. 3, serial. No. 153465, had been overhauled in September 1975, and had been installed on N901MA in November 1975; it had accumulated 85 hours since installation.

The documents from the propeller overhaul facility indicated that the No. 1 propeller had been inspected magnetically (Magnaflux), but the specific parts inspected were not listed. Interviews with the overhaul facility's management personnel and the magnetic inspection facility's personnel established that the blades had been magnetically inspected, but that the rubber deicing boots, which cover about 45 inches of the intoard portion of the 75-inch blades' leading edge, had not been removed from the blades during the inspection. Personnel from both facilities stated that the rubber boots usually were not removed from the blades if the heating elements checked out electrically and if the rubber material had not been damaged or frayed.

Publication 5-3B3-550, dated March 1, 1962, is Curtis-Wright's most recent overhaul manual for C632-S propellers. Part 3B3 of the manual pertains to the overhaul of the blades in general. Chapter 63.2, dated September 1, 1957, together with Model Difference Sheet 63.2-4MDS, dated November 1, 1960, describe the method to be used when magnetically inspecting the steel blades on the prcpeller. The instruction required that all steel blades be inspected over the entire external surface. The propeller overhaul facility did not have a copy of Chapter 63.2 or 63.2-4MDS in its library.

Mercur Airlines had the most recent propeller manual in its library; however, they had not determined which manuals or procedures were being used by the overhaul facility.

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14 CFR 121.367 and 14 CFR 145.2 specify that the certificate holder (operatr) shall have a program to insure that all maintenance, preventive maintenance, and alterations are performed in accordance with his (the operator's) manual.

14 CFR 121.363 places the responsibility for the airworthiness of an aircraft and its components on the certificate holder. It provides for the certificate holder to take arrangements with others to perform the required maintenance o.s. ions; however, it specifies that these arrangements do not relieve the certificate holder of the responsibility for assuring that the aircraft is airworthy.

The overhaul facility was under the surveillance of the maintenance inspectors of the Federal Aviation Administration's (FAA) Santa Monica General Aviation District Office. The Safety Board found no evidence that the FAA had noted or had informed the management of the overhsul facility that the overhaul facility did not possess the most current overhaul manual.

1.7 Meteorological Information

Meteorological observations at both the Hollywood-Burbank and Van Nuys Airports are made by FAA control tower personnel who have been certified by the National Weather Service.

At 102, the Burbank weather observation for February 8, 1976, was: "1,000 feet scattered, estimated 7,000 feet overcast, visibility--4 miles, light rain and fog, temperature--56°F, wind--180° at 4 kn, altimeter setting--29,97 in."

The Van Nuys weather observation was: "600 feet scattered, 1,000 feet scattered, estimated 8,000 feet overcast, visibility--10 miles, light rainshowers, temperature--55°F."

At 1045, an observation for Van Nuys was: "Special, 1,200 feet scattered, 10,000 feet overcast, visibility--10 miles, rainshowers, wind--130° at 4 kn, altiweter setting--29.93 in."

The accident occurred during daylight hours, under overcast skies, and in rainshowers.

1.8 Aids to Navigation

Not applicable.

1.9 Communications

Air-to-ground communications and land-line communications between the Hollywood-Burbank Tower and the Van Nuys Tower were normal.

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1.10 Aerodrome and Ground Facilities

Hollywood-Burbank Airport, elevation 775 feet m.s.l., has two runways -- 15/33 and 07/25. Runway 15/33 is 6,088 feet long and 150 feet wide, and has an asphalt surface. Runway 07/25 is 6,555 feet long and 150 feet wide and has an asphalt surface.

Van Nuys Airport, elevation 800 feet m.s.l., has two parallel runways -- 16/34, 16R/34L is 8,000 feet long and 150 feet wide and has an asphalt-concrete surface. 16L/34R is 4,000 feet long and 75 feet wide, and has an asphalt surface.

Instrument approach aids were available at both airports; however, they were not involved in this accident.

1.11 Flight Recorders

N901MA was not equipped with a flight data recorder, nor was it required. It was equipped with a United Data Control cockpit voice recorder, model 557Z, serial No. 1035. The recorder was not damaged by impact or ground fire. The tape was of good quality and contained a record of the entire flight beginning with the pre-engine start checklists. (See Appendix D.)

1.12 Wreckage

1.12.1 Components Seperated in Flight

The No. 3 engine, engine cowling, propeller, two pieces of lower fuselage skin, two pieces of the right (inboard) side cowling of the No. 2 engine, and the No. 2 propeller alternator separated from the aircraft during the initial takeoff from the Hollywood-Burbank Airport. Debris from the No. 3 engine was scattered across the intersection of runways 15/33 and 07/25.

The No. 1 blade of the No. 3 propeller was found on the runway. This blade had a chordwise fracture 43 inches from its clip. A 10-by 1.5-inch section was missing from the trailing edge of the blade. The remainder of the trailing edge was curled forward over the thrust face. A spanwise crease, about 24 inches long, extended outward from the fracture. There was a 9-inch cut through both faces of the blade and midway along the crease. At the leading edge, adjacent to the fracture, the blade was curled, torn, and kinked. Red paint, which covered the tip of the blade, was cubbed and scraped in a random pattern. Red paint was also found on the two pieces of the right (inboard) side cowling from the No. 2 engine which were recovered near the runway intersection.

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These two pieces of cowling had been penetrated from the outside. Directly in line with this rupture in the cowling, the front accessory case of the engine had beeo penetrated and a large hole was punctured in the casing. Fragments of the case material were found inside the engine case. The No. 2 propeller electrical junction box was flattened and bent inward through the hole. The terminal blocks were broken and several of the terminals disconnected. The drive gears for the oil scavenge pump, which are located at the bottom of the accessory case, were disengaged.

1.12.2 Main Wreckage

The aircraft came to rest on a magnetic heading of 232°, about 50 feet from the western edge of the Woodley Municipal Go'f Course and 1,200 feet south of Victory Boulevard in Van Nuys, California. The crash site is about 1-mile south of the threshold of runway 34L at the Van Nuys Airport. The elevation of the wreckage site was about 715 feet m.s.l.

The air aircraft had touched down on a magnetic heading of 278° and continued on that heading for about 1,710 feet until it struck the foundation of a partially constructed building. The aircraft rotated 46° to the left and slid about 140 feet; it came to rest against a house trailer.

A ground track, made by the outboard tire of the left main landing gear, began about 1,850 feet from the house trailer; the track was the first indication of ground contact. The main landing gear struts separate from the aircraft when it struck the concrete foundation. The wings, empennage, and fuselage, aft of fusclage station 261, remained essentially intact. The fiaps were retracted.

The fuselage was torn or broken across the entire width of the aircraft' at station 261. The forward portion of the fuselage was bent downward. The cockpit and forward portion of the passenger cabin were destroyed by impact.

The lower skin of the fuselage and the floor of the forward baggage compartment was torn and folded inward. The edges of the separation were jagged and the surfaces of the separation had deposits of a substance that appeared to be red paint.

Both horizontal stabilizers were streaked with oil; the left side of the fuselage was streaked with hydraulic fluid.

The left side fuselage tunnel, which is in the general area of the fuselage ice plate and below the cabin floor, had been punctured. The following lines are routed through this area: Nose gear actuatic.

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system, engine manifold pressure, emergency airbrake, and almost all of the cockpit electrical wiring. The hydraulic pressure for the wheel brakes and nose wheel steering are taken from the nose gear actuation line.

Many of the lines and much of the electrical wiring in the left side fuselage tunnel had been cut by the propeller blade. However, impact and fire damage prevented the identification of the lines and electrical wires that had been cut.

The emergency locator transmitter (ELT) was intact in its mounting and the antenna was connected. The ELT control switch was in the "Arm" position; however, the ELT did not activate. When tested by impact loads imposed from all directions, the unit did not activate; however, when tested in the manufacturer's test rig, the unit activated.

1.13 Medical and Pathological Information.

The cockpit crewmembers sustained fatal traumatic injuries when he aircraft hit the concrete foundation. Pathological examination showed no evidence of preexisting or incapacitating diseases. The C/R confirmed the pathological findings that all flightcw members were functioning during the emergency. The toxicological analyses were negative.

The two flight attendants sustained multiple contusions and abrasions to their heads and legs. The nonrevenue passenger sustained a slight confusion to the back of his head.

Three firemen sustained serious injuries consisting of second degree burns and damage to their air passages; seven firemen received minor burns. The occupant of the house trailer received abrasions when he evacuated the trailer.

1.14 Pire

There was no fire as a result of impact. The Los Angeles City Fire Department (LACFD) responded to the accident scene with 18 units. The first units arrived about 3 minutes after the accident. The fuel lines in the left wing's leading edge had ruptured and fuel had leaked under the forward section of the wreckage. Firemen and survivors described the fuel fumes outside the aircraft as "very strac"; " however, when they entered the aircraft in an attempt to rescue the flightcrew members, they did not smell fuel.

In order to reach the flighters members, a decision was made to separate the cockpit from the fuselage by using a carbide saw. 5/

5/ The type of carbide saw used to cut the fuselage had been tested and used by the LACFD for many years. It reportedly did not create sparl:3 unless it contacted ferrous metal during cutting operations.

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Before the cut was made, the area around the nose and wings of the aircraft was blankated with aqueous film-forming foam. In addition to the foam, firemen, who held charged handlines, and the crash unit, which had a turret and ground nozzles, were positioned around the nose of the aircraft. The aircraft's skin was sawed from the right forward door to the top of the fuselage. The cut was located approximately 3 inches behind the cockpit/fuselage production splice. No sparks were generated during this activity. A ladder was then placed against the left side of the fusc㘣㼱, aft of the cockpit, and a second cut which angled on the left side of the fuselage toward the production splice was started. Shortly thereafter, a large continuous stream of sparks was generated and fell to the ground. Immediately, a fire erupted and engulfed the firemen who were on or near the nose of the aircraft. The fire was extinguished in seconds by the firemen that had been prepositioned. The fire began about 20 minutes after the accident.

1.15 Survival Aspects

A California Highway Patrol helicopter landed within seconds of the crash, and its crew attempted to get into the cockpit. A person at the scene went to the rear exit and assisted the ca' in occupants away from the aircraft. Several other organizations discapched helicopters and ambulances to the scene, and the equipment stood by to assist in the evacuation. Helicopters were used to airlift seriously injured firement to the hospital.

The senior flight attendant was seated in the aisle seat, row 13, right side. Her legs were pinned under her seat and her weight was being supported by her seatbelt. Her situation was further complicated because the seats in row 12 had fallen toward her. The second flight attendant was seated in the aisle seat, row 14, right side. Her legs also were pinned under the seat when it tilted forward and caused her weight to be suspended on the seatbelt. She experienced some difficulty freeing herself because her weight was on the belt and because the seatbelt fabric was difficult to pull through the buckle. After she freed herself, she assisted the senior flight attendant. Both went to the left rear door, opened it without difficulty, and exited.

The nonrevenue passenger was not trapped nor did he have any difficulty releasing his seatbelt. He climbed over his seatback to reach the rear exit because the aisle was blocked by debris and loose seats.

Six rows of seats were torn from their fittings during the crash. The cbin, forward of row 7, was damaged extensively. The evacuation slide had fallen from the attach fittings on the door. It was not used in the evacuation.

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1.16 Test and Research

1.16.1 Metallurgical Tests

Safety Board metalliurgists examined the No. 1 blade of the No. 3 propeller. Microscopic examination of the chordwise fracture disclosed futigue markings emanating from the leading edge of the blade. Most of the fractures at the leading edge had been destroyed by mechanical damage following blade separation. In order to determine the precise origin of the fracture, a crack in the existing fracture plane was opened. Detailed examinations of the exposed fracture region disclosed that the fatigue began along the inside radius of the stcel blade shell in an area which contained trazing material. Fractographic and metallographic examination showed that the fatigue probably began in the steel blade as a result of prior cracks in the brazing material which intersected mismatches in the steel formed during the manufacture of the blade shell. Material properties of the steel blade met engineering drawing requirements.

1.16.2 Analysis of Red Paint S�ars

On March 5, 1976, the No. 1 blade of the No. 3 propeller, a section of metal from along the separation in the baggage floor, and sections of the right side cowling of the No. 2 engine were taken to the Federal Bureau of Investigation (FBI) laboratories for examination of the paint on the propeller and the red smears on the other pieces. The FBI report concluded that the paint particles from the metal from the baggage compartment floor could have originated from the propeller blade. The smears on the No. 2 engine cowling were of insufficient quantity to determine type or source.

2. ANALYSIS AND CONCLUSIONS

2.1 Analysis

The flight screw members were qualified and properly certified for the intended flight. The aircraft was properly equipped for the intended flight and the weight and c.g. were within the prescribed limits.

2.1.1 The Accident

The accident sequence was initiated when the No. 1 blade of the "3, 3 propeller separated at a point 43 inches from the propeller tip. Metallurgical examination showed that the failure of the No. 1 blade resulted from fatigue cracks that had origine along the inside radius of the steel blade shell. These fatigue cracks initiated from other cracks in the brzing material that intersected mismatches formed during the manufacture of the blade sh'1.

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The fatigue crack should have been directed during the last blade inspection. The crack probably remained undetected during the magnetic particle inspection because the overhaul facility did not remove the rubberized deciding boot along the lower portion of the blade. The crack was not visible when the propeller was installed on the engine.

The loss of one blade of the propeller caused an imbalance that instantly tore the No. 3 engine from the aircraft. The failed blade penetrated the lower fuselage near station 261 and traversed the width of the aircraft's fuselage. This was evidenced by the strip of lower fuselage skin found on the Hollywood-Burbank Airport and the red paint smears on the surfaces of the cut in the forward baggage compartment floors. The paint type matched that on the tips of all propeller blades; however, the No. 1 blade had the only scratch and scrape marks in the painted surface that would result from cutting through the fuselage.

As the blade traversed the fuselage, it severed most of the hydraulic and pneumatic lines and much of the electric wiring in the left fuselage tunnel. Although the damage inflicted during the impact and postaccident fire precluded identification of the lines and wirea that were severed, the nose gear actuation line (hydraulic), engine manifold pressure line (pneumatic), emergency airbrake (pneumatic), and the propeller control (electric) were among those damaged when the blade passed through the fuselage. This damage caused the loss of propeller control, including reversing, and the loss of hydraulic and emergency airbrakes.

The propeller blade exited the left side of the fuselage and penetrated the right inboard side of the No. 2 engine. As the blade penetrated the No. 2 engine's front accessory case, it caused the No. 2 propeller's alternator to separate and the drive gears of the oil scavenge pump to disengage. When the front accessory case was penetrated engine oil was lost in about 4 minutes. The lack of oil prevented lubrication of the engine components, and the engine failed shortly after the crew abandoned the attempted emergency landing at the Hollywood-Burbank Airport.

The separation of the No. 2 propeller junction box caused the propeller to remain fixed in pitch, regardless of any action the crew could take. This fixed pitch resulted in an additional drag component on the aircraft when the No. 2 engine failed and stopped rotating.

Considering the situation, the captain's decision to remain in the traffic pattern at Hollywood-Burbank Airport and to land as soon as possible was prudent.

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However, after landing with neither hydraulic nor emergency trakes available and with the aircraft being accelerated by forward thrust when reverse power was applied, and considering the runway length end the obstacles at the departure end of the runway, the captain had to decide instantly whether: (1) To apply maximum available power to the three operating engines and takeoff, or (2) to keep the aircraft on the ground and attempt to avoid the obstacles and buildings at the end of the runway through the use of differenticl engine power. In retrospect, the latter alternative may have been more prudent in view of the impending failure of the No. 2 engine.

In this respect , after the No . 3 engine failed , had the crew monitored the engines and hydraulic instruments more closely during the 3 minutes the aircraft was circling to make the emergency landing , they would have known that the oil in the No . 2 engine had been lost and that a severe hydraulic system problem existed . The hydraulic system problem would have been indicated by the loss of hydraulic fluid quantity and system pressure. Had the captain been aware of these conditions before he attempted to land , he may have elected to stay on the ground rather than again becoming airborne with an impending second engine failure .

Although the crew selected landing gear up after the second takeoff, the landing gear remained extended. As long as the No. 2 engine continued to operate, there was sufficient power for the aircraft to accelerate and climb. However, when the No. 2 engine failed, the drag that was created by (1) the flat plate area of the No. 3 nacelle, (2) the flat blade angle of the No. 2 propeller blades, and (3) the extend-landing gear was more than the two remaining operating engines could overcome. Paced with insufficient power to maintain altitude and airspeed, the crew had no alternative but to attempt a landing on the golf course. In addition, since the hydraulically operated windshield wipers were inoperative, rain restricted the forward visibility and the crew probably did not see the building before they reduced the throttles on engines Nos. 1 and 4.

The postcrash fire was ignited by sparks that were generated when the blue of the table saw contacted a steel bolt and steel nut which connected the cockpic to the cabin structure at the manufacturing splice. The sparks fell to the ground and ignited the fuel that had leaked from the aircraft.

Although firemen had covered the area around the nose of the aircraft with foam, the affectiveness of the foam was deteriorated by the movement: of the firesen through the mixture, by the action of the wind and rain, or by a combination of these elements. The disturbance of the foam allowed the highly volatile fumes of the spilled aviation gasoline to escape from under the layer of foam and to be ignited.

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The areas where the fuselage could be safely cut with a saw were not marked and the firemen did not know where they could saw without hazard. Since steel bolts are commonly used to connect the sections of the fuselage at manufacturing a plices, rescue personnel should be aware of areas where saws can be used without encountering ferrous festeners.

2.1.2 Inadequate Overhaul Procedures

The FAA certified overhaul facility contracted by the carrier to perform the required maintenance on the Curtiss-Wright electric propellers did not have a current or complete overhaul manual. Although the Federal Air Regulations permit a carrier to contract for maintenance work, they do not relieve the carrier of the responsibility for the airworthiness of his aircraft. The regulations make it incumbent upon the carrier to insure that a contractor is using current manuals, equipment, and procedures when performing maintenance work for the carrier.

The carrier, in this instance, did have the current manuals in its library; however, they had not inspected and assured the adquacy of their contractor's library or procedures. The overhaul facility was under surveillance of FAA inspectors. The lack of proper manuals and the use of improper procedures in overhauling the propeller was not detected by these inspectors.

The Safety Board believes that a review of applicable maintenance manuals and procedures for older aircraft and their subsystems must be more rigorously pursued by FAA approved repair stations and certificate holders, particularly when maintenance personnel do not have the opportunity to stay familiar with equipment or procedures.

2.2 Conclusions

(a) Findings

1. The aircraft was not airworthy at takeoff because of a fatigue crack in the No. 1 blade of the No. 3 propeller.

1. The fatigue crack was underneath the deicer boot and was not detected because the overhaul facility that inspected the propeller did not remove the deicer boot before performing a magnetic particle inspection.

1. The propeller inspection was not conducted in accordance with the propeller manufacturer's published criteria. The inspection facility did not have the manufacturer's current inspection publications.

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1. Neither the carrier nor the FAA detected the lack of current inspection publications in the repair facility.

1. The No. 1 blade of the No. 3 propeller failed just after takeoff and the loss of the blade caused an imbalance that caused separation, almost instantly, of the No. 3 engine from the aircraft.

1. The No. 1 blade of the No. 3 engine penetrated the lower fuseiage of the aircraft and penetrated the lower inboard side of the No. 2 engine.

1. As the blade passed through the fuselage, it severed pneumatic, hydraulic, and emergency airbrake lines as well as the electrical wiring for propeller controls and some engine instruments.

1. The flightcrev was not aware of the cause of this damage or that the No. 2 engine had been damaged.

1. The pilot attempted an emergency landing at Hollywood-Burbank Airport.

1. The pilot took off again after he found that he could not reverse the propellers and he had neither normal nor emergency airbrakes, and could not stop in the runway.

1. The pilot elected to divert to Van Nuys Airport where a longer clear runway was available.

1. The No. 2 engine failed en route to Van Nuys from damage caused by the propeller blade from the No. 3 engine.

1. The pilots could not feather the No. 2 propeller and the propeller stayed at a fixed-blade angle which created an additional drag component on the aircraft.

1. During the diversion to Van Nuys, the landing gears remained extended due to a loss of hydraulic system pressure and fluid through the severed hydraulic lines made by the propeller blade from the No. 3 engine. The crew did not know that the gear was extended and created additional unexpected drag on the aircraft.

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1. The drag created by the flat-plate area of the no. 3 engine nacelle, the windmilling No. 2 propeller, and the extended landing gear was more than the power from two operating engines could overcome.

1. The pilot attempted to land on a golf course about 1 mile short of runway 34L at the Van Nuys Airport when they determined that they could not stay airborne.

1. The aircraft was destroyed and the flightcrew killed by impact.

1. A fire occurred about 20 minutes after the accident when a carbide saw blade struck a steel bolt in the aircraft structure igniting fuel during an attempt to remove the flightcrew from the wreckage.

(b) Probable Cause

The National Transportation Safety Board determines that the probable cause of this accident was the degraded performance of the aircraft after two engines failed. The dual failure was precipitated by the in-flight failure of the No. 1 blade of the No. 3 propeller assembly. The failure of the propeller blade resulted from a fatigue crack, which originated in the leading edge under the delicer boot. The crack had not been detected during an improperly performed overhaul.

3. RECOMENDATIONS

As a result of this accident, the National Transportation Safety Board recommended on June 3, 1976, that the Federal Aviation Administration:

"Review the overhaul manuals for all metal propeller blades that are sheah equipped and insure that the manuals require that the surfaces of these blades beneath the sheaths be inspected either by removal of the sheath or by an alternate method which will detect cracks underneath the sheath. (Class 1-Urgent Followup.) (A-76-77)

"Remind 14 CFR 121 certificate holders of their responsibility for insuring the adequacy of maintenance of their aircraft and components, even if the maintenance is contracted to outside repair stations. (Class 1-Urgent Followup.) (A-76-78.)

• 17 -

"Review FAA surveillance procedures for certified repair stations to insure that they are adequate and that all repair stations maintain and use complete and current maintenance manuals. (Class II--Priority Followup.) (A-76-79.)"

BY THE NATIONAL TRANSPCKTATION SAFETY BOARD

/ε/ WEBSTER B. TODD, JR. Chairman

/s/ 2AY BAILEY V:ce Chairman

/s/ $\frac{\text{FRANCIS H. McADAMS}}{\text{Member}}$

/s/ PHILIP A. HOGUR Member

WILLIAM R. HALLEY, Member, did not participate in the adoption of this report.

August 18, 1976.

• 19 -

APPENDIX A

INVESTIGATION AND HEARING

1. Investigation

The National Transportation Safety Board was notified of the accident at 1430 e.s.t., February 8, 1976.

Working groups were established for operations/air traffic control, witnesses, human factors, powerplants/structures/maintenance records, systems, and cockpit voice recorder.

Parties to the investigation were: Mercer Airlines, Inc.; Federal Aviation Administration; Pratt and Whitney Aircraft Division-United Technologies Corporation; and Curtis-Wright Corporation.

The Los Angeles County Coroner's Office, Los Angeles Police Department, and the Los Angeles City Fire Department assisted the Safety Board during the investigation.

2. Hearing

No hearing was held.

• 20 -

APPENDIX B

CREW INFORMATION

Captain James R, Seccembe

Captain James R. Secombe, 38, was employed by Mercer Airlines on October 1, 1967. He hold ATP Certificate No. 1430499 issued on November 5, 1958, and was type rated on the IC-6 on April 23, 1970. He was assigned and qualified as a captain on April 24, 1970. He completed his last proficiency check on October 27, 1975, and his last line check on November 28, 1975. Captain Secombe's most recent first-class medical certificate was issued on August 4, 1975, with the limitation that "Holder shall wear correcting glasses while exercising the privileges of his airman certificate."

Captain Secombe had flown 20.8 hours during February and 45.1, 104.8, and 136.3 flight-hours in the last 30, 60, and 90 days, respectively. He had a total of approximately 20,558 flight-hours.

First Officer Jack R. Finger

First Officer Jack R. Finger, 55, was employed by Mercer Airlines on February 9, 1969. He held ATP Certificate No. 260308 issued on September 15, 1961, and was assigned and qualified as a second-in-command on the DC-6 on August 6, 1973. He completed his last proficiency check on October 25, 1975. First Officer Finger's most recent first-class medical certificate was issued on December 9, 1975, with the limitation that "Holder shall wear correcting glasses for near and far vision while exercising the privileges of his airman certificate.

First Officer Finger had flown 3.0 hours during February and 18.9, 59.8, and 67.8 flight-hours in the last 30, 60, and 90 days, respectively. He had a total of approximately 6,600 flight-hours.

Flight Engineer Arthur M, Bankers

Flight Engineer Arthur M. Bankers, 53, was employed by Mercer Airlines on June 30, 1975. He held Flight Engineer Certificate No. 1344191, issued on June 22, 1956, and was assigned and qualified as a DC-C Flight Engineer on June 30, 1975. He completed his least flight check on November 6, 1975. Flight Engineer Bankers most recent second-class medical certificate was issued on June 23, 1975, with the limitation that "Holder shall wear correcting glasses while exercising the privileges of his airman certificate."

Flight Engineer Bankers had flown 9.1 hours during February and 42.9, 65.9, and 91.4 flight-hours in the last 30, 60, and 90 days, respectively. He had a total of approximately 9,600 flight-hours.

• 21 -

APPENDIX C

AIRCRAFT INFORMATION

N90IMA a Dcuglas DC-6/YC-112A, serial No. 36326, was manufactured on February 11, 1946, under Army Air Corps Serial No. 45-873. It was manufactured under a military contract as a prototype aircraft for the U.S. Army Air Corps. It was later given to the Civil Aeronautics Administration, which used it exclusively as a ground trainer at the Aeronautical Center, Oklahoma City, Oklahoma. It was subsequently sold at auction as surplus property to Conners Airlines, Inc., of Miami, Florida.

Up to this time the aircraft had never been registered under civil certification. Conners Airlines modified the aircraft and it was certified in the transport category by the addition of Note 9 to the Federal Aviation Agency Aircraft Specification No. A-781. The aircraft was certified on August 20, 1956. It was operated by Conners Airlines and later by several other operators under U.S., Ecuadorian, Spanish, and Canadian registrations until it was acquired by Mercer Airlines in 1967.

N901MA was powered by four Fratt and Whitney R2800 engines. Each engine was equipped with Curtiss-Wright electric propellers, type C632-S.

Engine and propeller data were as follows:

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APPENDIX D

PARTIAL TRANSCRIPT OF

COCKPIT VOICE RECORDER

TAKEN FROM THE

MERCER AIRLINES DOUGLAS DC-6, N901MA

VAN NUYS, CALIFORNIA

FEBRUARY 8,1976

FROM 1834:55 TO 1844:37 G.M.T.

$$ (1034:55-1044:37 P.S.t.) $$

• 23 -

APPENDIX D

LEGEND

CAM Cockpit area microphone voice or sound source

RDO Radio transmission from Mercer Airways DC-6

-1 Voice identified as Captain

-2 Voice identified as First Officer

-3 Voice identified as Flight Engiaeer

-4 Cabin Attendant

-? Voice unidentified

UNK Unknown

• Unintelligible word

Nonpertinent word

% Break in continuity

( ) Questionable text

( ( ) ) Editorial insertion

--- Pause

LP Light airplane call sign unknown

BG Burbank ground control

BT Burbank Tower

VNT Van Nuys Tower

Warning

The reader of this report is cautioned that the transcription of a CVR tape is not a precise science but is the best product possible from an PSB group investigative effort. The transcript or parts thereof, if taken out of context, could be misleading. The attached CVR transcript should be viewed an accident investigation too to be used in conjunction with other evidence gathered during the investigation. Conclusions or interpretations should not be made using the transcript as the sole source of information.

INTRA-COCKPIT

AIR-GROUND COMMINICATIONS

TIME & SOURCE CONTENT

1834:55 BT Niner zero one, make a rolling takeoff

RDC-2 Niner zero one, say again

1835:00 BT Can you make a rolling takeoff, uh, PSA on final four miles or so

RDO-2 Okay, now we're (running) ((Extraneous conversation))

APPENDIX D

INTRA-COCKPIT

AIR-GROUND COMMUTICATIONS

TIME & SOURCE CONTENT

1836:03 PT PSA four five one go around-- go around four five one

PSA-451
Four fifty-one on the go
1836:09
RID-2
Niner zero one --- correction, niner
zero one returning --- requesting uh
may we return to the field --- declaring
an emergency --- I'd like runway seven
we lost an engine
BT
Sir, you're cleared to land, PSA go
around, circle the airport, please

INTRA-COCKPTT

AIR-GROUND COMMUNICATIONS

TIME & SOURCE CONTENT 1836:21 RDO-2 Nine oh one cleared to land BT Nine oh one, bunch of equipment, bunch of trash all over the intersection 1836:51 RDO-2 Niner zero one requesting equipment please 1836:55 BT Yes sir, it's on the way and I see there's debris at the intersection, debris on the intersection

APPENDIX D

INTRA-COCPIT

AIR-GROUND COMMUNICATIONS

APPENDIX D

APPENDIX p

INTRA-CCCKPIT

AIR-GROUND COMMITCATIONS

INTRA-COCKPIT

AIR-GROUND COMMITCATIONS

TIME & SOURCE

CONTRHT

TDZ & SOURCE

COSTIGET

CAM-2

See the runway?

CAM-2

I got it

CAM-2

All zIght

CAM-3

Look at that number three fuel tank

CAM-2

Do you want the gear?

1838:05

CAM-2

Rügt now

CAM-2

Okay, gear coming down

$$CAM=2$$

Listen we're going to reverse the outboards only. Hope the gear comes down all right

CAN-2

There it is

CäKıI

Flaps twenty. Make them --- yeah, just twenty, right now, okay?

1838:26

CAM-1

All right give me, uh, flaps full

CAM-2

Flaps full

CAM-2

Manifold, uh, two five, all right?

CAM-2

Speeds, Jack

CAX=2

One forty-five, one forty-five. Slow down quite a bit

INTRA-COCKPIT

AIR-GROUND COMMUNICATIONS

APPENDIX D

INTERA-COCPTT

AIR-GROUND COMMUNICATIONS

APPENDIX D

DWRA-COCKPIT

AIR-GROUND COMMICATIONS

INTRA-COCKPIT

TIME & SOURCE CONTENT 1840:35 CAM-3 Got no # oil pressure on number two engine CAM-1 What? CAM-3 No oil pressure on number two 1840:41 CAM-1 No BMEP either CAM-1 We're going to lose that #! CAM-2 You want to try one five? we can get it --- CAM-1 I don't know how we'll make it, Jack 1840:54 CAM-1 I want three four in --- ah where the # am I? I want three four. No, no, no, no! Three four at Van Nuys!

AIR-GROUND COMMUNICATIONS

TIME & SOURCE

CONTENT

1841:03

RD0-2 Niner zero one, we'll take three four at Van Nuys

1841:06

BT All right, six, and the wind is zero six zero at four

1841:11

RDO-2 Roger, zero six zero at four

APPENDIX D

-34-

I'MIRA-OCCIPTI

AIR-GROUND COMUNICATIONS

INTRA-COCKPIT

APPENDIX D

INTRA-COCKPIT

AIR-GROUND COMMUNICATIONS

TIME & SOURCE CONTENT 1842:25 RDO-2 We're not going to make one six right, we're going have to try for three four VNT (Cessna nine two mike) make a full stop VNT Cessna seven kilo yankee make a full stop this time. Also acknowledge 1842:43 VNT Cessna Charlie Charlie, be prepared for a possible go around for you, acknowledge CCC Charlie Charlie roger, Possible go around --- what's going on? 1842:51 VNT Ah it's a Mercer DC, uh, six, I think, going to use runway three four, got an engine problem, I don't have him in sight yet. I'll advise you if he gets close enough for you to have to go around 1843:10 This is niner zero one, would you clear the frequency for a minute, we are in an emergency. We are in an emergency and are just barely hanging in here

AIR-GROUND COMMUNICATIONS

TIME &

SOURCE CONTENT

RD0-2 Inner zero one, we are approaching the airport from the uh --- from the east and we'll be landing on runway three four, landing runway three four that's about all we're going to make

1843:22 VNT Runway three four left, clared to land on runway three four left

1843:29
300-2
Roger and we have no brakes at the present time, no brakes at the present time, niner zero one

VNT Cessia Charlie Charlie you're going to have to go around this time, enter right traffic again report downwind west

1843:37 CCC Charlie Charlie roger, going around VNT (Cherokee) three six cleared to land full stop

VNT (Cherokee) three six that's approved VNT Cessna

APPENDX D

INTRA-COCKPIT

AIR-GROUND COMONICATIONS

INTRA-COCKPIT

TIME 2

SOURCE

CONTENT

1844:28

CAM

((Initial sound of impact))

CAM-1 Gear

그런니:36

CAM

((Sound of second impact))

CAM?

表

1844:37

CAM

$$ (\text{Sound of third impact})) $$

End of Tape

AIR-GROUND COMMUNICATIONS

TIME &

SOURCE

CONTENT

APPKDIX D

• 40 “