AMERICAN AIRLINES FLIGHT 191
On May 25, 1979, American Airlines Flight 191 crashed on takeoff from Chicago O'Hare International Airport, Illinois, USA. All 271 people on board were killed, along with two people on the ground. With 273 fatalities, it is the deadliest aviation accident to have occurred in the United States.
The Flight 191 was a scheduled domestic passenger flight from Chicago O'Hare International Airport, Illinois to Los Angeles International Airport, California. The pilot-in-command was captain Walter Lux, who had been flying the DC-10 since its introduction in 1971. Captain Lux had logged around 22 000 flying hours, of which about 3 000 were in a DC-10. First Officer was James Dillard with 9 275 hours of flying experience, and the flight engineer was Alfred Udovich, who had 15 000 total flight hours to his credit. The aircraft involved was a McDonnell Douglas DC-10-10, registered as N110AA. The aircraft had been delivered new to American Airlines on February 25, 1972. At the time of the accident, the aircraft had flown just under 20 000 hours.
At 14:59 hours local time Flight 191 taxied from the gate at O'Hare Airport. The flight was bound for Los Angeles, California, with 258 passengers and 13 crewmembers on board. Maintenance personnel who monitored the flight's engine start, push-back, and start of taxi did not observe anything out of the ordinary. The weather at the time of departure was clear. Flight 191 was cleared to taxi into position on runway 32R and hold. At 15:02, the flight was cleared for takeoff. The takeoff roll was normal until just before rotation, just as the aircraft reached takeoff speed, the engine one and its pylon assembly separated from the left wing, ripping away a section of the leading edge with it. The combined unit flipped over the top of the wing and landed on the runway. In addition to the engine's failure, several related systems failed. The aircraft climbed to about 100 m above ground level while spewing a white mist trail of fuel and hydraulic fluid from the left wing. The engine separation severed the hydraulic fluid lines that controlled the leading-edge slats on the left wing and locked them in place, causing the outboard slats to retract under air load. The retraction of the slats raised the stall speed of the left wing to about 294 km/h. As a result, the left wing entered a full aerodynamic stall. With the left wing stalled, the aircraft began banking to the left, rolling over onto its side until it was partially inverted at a 112 degrees bank angle with its right wing over its left wing. The aircraft eventually slammed into a field around 1 400 m from the end of the runway. Large sections of aircraft debris were hurled by the force of the impact into an adjacent trailer park, destroying five trailers and several cars. The DC-10 had also crashed into an old aircraft hangar located at the edge of the airport at the former site of Ravenswood International Airport, which was used for storage. The aircraft was completely destroyed by the impact force and ignition of a nearly full load of 21 000 gallons of fuel. No sizable components other than the engines and tail section remained. In addition to the 271 people on board the aircraft, two employees at a nearby repair garage were killed, and two more were severely burned.
National Transportation Safety Board determined that the damage to the left-wing engine pylon had occurred during an earlier engine change at the American Airlines aircraft maintenance facility in Tulsa, Oklahoma, between March 29 and 30, 1979. On those dates, the aircraft had undergone routine service, during which the engine and pylon had been removed from the wing for inspection and maintenance.
The removal procedure recommended by McDonnell Douglas called for the engine to be detached from the pylon before detaching the pylon itself from the wing. However, American Airlines, as well as Continental Airlines and United Airlines, had developed a different procedure that saved about 200 man-hours per aircraft. This new procedure involved the removal of the engine and pylon assembly as a single unit, rather than as individual components. United Airlines' implementation involved the use of an overhead crane to support the engine and pylon assembly during removal and installation. The method chosen by American Airlines and Continental Airlines relied on supporting the engine and pylon assembly with a large forklift. If the forklift was incorrectly positioned, the engine and pylon assembly would not be stable as it was being handled, causing it to rock like a see-saw and jam the pylon against the wing's attachment points. Positioning had to be extremely accurate, or structural damage could result. During the maintenance of accident aircraft N110AA, although the forklift remained stationary, the forks supporting the entire weight of the engine and pylon moved downward slightly due to a normal loss of hydraulic pressure associated with the forklift engine being turned off. This caused a misalignment between the engine/pylon and wing. Because of that the pylon was jammed on the wing and the forklift had to be repositioned. Whether damage to the mount was caused by the initial downward movement of the engine/pylon structure or by the realignment attempt is unclear. Regardless of how it happened, the resulting damage, although insufficient to cause an immediate failure, eventually developed into fatigue cracking, worsening with each takeoff and landing cycle during the 8 weeks that followed. When the attachment finally failed, the engine and its pylon broke away from the wing. The structure surrounding the forward pylon mount also failed from the resulting stresses.
The investigation also revealed other DC-10s with damage caused by the same faulty maintenance procedure. Inspection of the DC-10 fleets of these three airlines revealed that while United Airlines' hoist approach seemed to be harmless, several DC-10s at both American Airlines and Continental Airlines already had fatigue cracking and bending damage to their pylon mounts caused by similar maintenance procedures. Removal of the engines and pylons as a unit was not an approved Maintenance Manual procedure. The field service representative from McDonnell Douglas stated the company would "not encourage this procedure due to the element of risk" and had so advised American Airlines. McDonnell Douglas, however, "does not have the authority to either approve or disapprove the maintenance procedures of its customers." The faulty procedure was banned, and in response to this accident, American Airlines was fined $500 000 by the U.S. government for improper maintenance procedures.
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