Science Fair Project Encyclopedia
American Airlines Flight 191
The flight originated from O'Hare International Airport in Chicago, Illinois to Los Angeles International Airport in Los Angeles, California. The aircraft was a Douglas DC-10-10, identified as N110AA on that day.
On takeoff from O'Hare the plane carried 258 passengers and 13 crew members. The captain was veteran Walter Lux, his first officer was James Dillard and the flight engineer was Alfred Udovich. At 15:02 CDT, the aircraft began its takeoff down Runway 32R (Right).
Shortly before the takeoff rotation began, with 6,000 feet of runway covered, tower controllers witnessed the number one engine (left wing) separate from the aircraft and fly up and over the wing to crash onto the runway. The aircraft continued in a normal climb momentarily to around 350 feet (AGL), as fuel and leaking hydraulic fluid spewed in a vapor trail behind the plane. Such an incident is survivable in a DC-10, the shift in center of gravity and mean aerodynamic chord was within tolerances, and the aircraft could have landed safely if the engine loss had not caused other failures. However, in subsequent flight simulation testing, only pilots who were aware of Flight 191's specific problems were able to successfully recover the stall.
The pilots aimed to reduce speed from 165 knots to the recommended engine-out climb speed of 153 knots, but the engine separation had severed the hydraulic lines that controlled the aircraft's leading-edge wing slats (retractable devices that increase a wing's lift during takeoff and landing). Further, the missing engine supplied the electricity to the captain's instruments - notably stall warning, slats disagreement, and stick shaker, which were only available to the captain and not replicated in the first officer's instruments. Unusually, the backup power to the captain's instruments was not engaged by the flight engineer. This meant that the pilots were unaware of the aircraft's true configuration.
As the hydraulic fluid bled away, the slats retracted on the left wing, raising that wing's stall speed from 124 knots to around 160 knots. As the pilots slowed the aircraft the left wing stalled, and with the right wing still providing lift the aircraft quickly entered an uncontrollable 112-degree left bank  and pitched nose-down from around 325 feet, slamming into an open field around 4,700 ft from the end of the runway at about 15:04 CDT after 31 seconds in the air. The aircraft disintegrated and burned, all 271 persons on board were fatally injured during the impact and explosion. In addition some wreckage was thrown into a nearby mobile home park killing two residents and seriously injuring two others.
The public impact of the accident was greatly enhanced by the dramatic video taken of the incident.
The NTSB Investigation
The resulting investigation by the National Transportation Safety Board (NTSB) was released on December 21 1979. It revealed the probable cause to be attributable to damage to the left wing engine pylon that occurred during an earlier engine change at American's aircraft overhaul facility in Tulsa, Oklahoma. The pylon was damaged due to a incorrectly executed engine removal procedure. The correct procedure called for removal of the engine prior to the removal of the engine pylon. To save time and costs, American Airlines instructed its mechanics to remove the engine together with the pylon all at one time. A large fork lift was used to hold the engine up while it was detached from the wing. During the procedure a crew shift change occurred, leaving the fork lift unmonitored for a period of time. A problem in the fork lift's hydraulic system caused it to tilt the engine while still under the wing. This exerted enough pressure on the engine pylon to create a large indentation and a serious fracture in its body. The fracture went unnoticed for several flights, getting worse with each flight that the plane had taken. During flight 191's takeoff, enough force was generated to finally cause the pylon to fail. With the failure of the rear pylon, the left engine detached from under the wing and tore away. With the loss of the engine and the position of the slats, the plane was destined for disaster. The NTSB concluded that given the circumstances of the situation, the pilots were not in any way to blame for the resulting accident.
Problems with DC-10s were discovered as a cause of the accident, including deficiences in both design specifications and maintenance procedures which made damage very likely. Since this tragedy happened just after a Western Airlines DC-10 had crashed in Mexico City and six years after a Turkish Airlines DC-10 crashed in Paris, the FAA quickly ordered all DC-10s to be stored (grounded) until all problems were solved. The result of the problem solving was an arguably more efficient and safe DC-10.
The crash in Chicago remains the largest single-aircraft air crash in United States history. Another flight with the same number, Delta Air Lines Flight 191, crashed at Dallas/Fort Worth International Airport in 1985. Neither company has ever used the 191 flight number again. In addition, Puerto Rican airline Prinair also had a fatal flight numbered flight 191.
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