S03E15 Chicago Air Crash: American Airlines Flight 191

February 4, 2013 | By | Comments More

American Airlines Flight 191, a DC-10, takes-off from Chicago’s O’Hare Airport. As the aircraft lifts off the runway the engine breaks free from the left wing and flies over and behind it, smashing onto the runway and leaving a gash in the wing leading edge. A leak of hydraulic fluid from the damaged wing leads to loss of hydraulic pressure, in turn causing the left wing slats to retract, depriving that wing of lift. The resulting asymmetric condition of the wings causes the DC-10 to roll rapidly to the left, becoming almost inverted. It crashes into a trailer park, killing all on board plus two on the ground. The cause is found to lie in time- and money-saving maintenance methods adopted by the airline, with the non-redundant design of the controls operating the DC-10’s flying surfaces ajudged a contributing factor.

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American Airlines Flight 191 was a regularly scheduled passenger flight from O’Hare International Airport in Chicago to Los Angeles International Airport. On May 25, 1979, the McDonnell Douglas DC-10-10 operating the flight crashed moments after takeoff from Chicago. All 258 passengers and 13 crew on board were killed, along with two people on the ground. Until the September 11 attacks, it was the deadliest air disaster in the history of the United States. It remains the deadliest aviation accident to occur on U.S. soil, as well as the second deadliest involving a DC-10, after Turkish Airlines Flight 981. It was also the third worst aviation disaster in history at the time, and is currently the tenth worst.

Investigators found that as the jet was beginning its takeoff rotation, engine number one on the left (port) wing separated and flipped over the top of the wing. As the engine separated from the aircraft, it severed hydraulic fluid lines and damaged the left wing, resulting in a retraction of the slats. As the jet attempted to climb, the left wing aerodynamically stalled while the right wing, with its slats still deployed, continued to produce lift. The jetliner subsequently rolled to the left and reached a bank angle of 112 degrees (partially inverted), before crashing in an open field near a trailer park near the end of the runway. The engine separation was attributed to damage to the pylon rigging structure holding the engine to the wing caused by faulty maintenance procedures at American Airlines.

While maintenance issues and not the actual design of the aircraft were ultimately found responsible for the crash, the accident and subsequent grounding of all DC-10s by the Federal Aviation Administration added to an already unfavorable reputation of the DC-10 aircraft in the eyes of the public caused by several other incidents and accidents involving the type. The investigation also revealed other DC-10s with damage caused by the same faulty maintenance procedure. Ultimately these problems were fixed and the aircraft type went on to have a long passenger career. It has since found a second career as a cargo airplane.

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The weather was clear, with a northeast wind at 22 knots (41 km/h). At 14:50 CDT, Flight 191 pushed back from gate K5 and was cleared to taxi to runway 32R. Maintenance crews present at the gate did not notice anything unusual during pushback, engine start, or taxi.

The flight began its takeoff roll at 15:02. Everything appeared normal until just after the plane reached takeoff speed, when the number one engine and the pylon assembly that attached it to the wing separated from the aircraft, ripping away a 3-foot (0.91 m) section of the leading edge of the left wing. Both the engine and pylon flipped over the top of the wing and landed on the runway. As the airplane was already above takeoff speed, the flight crew continued the takeoff. The airplane became airborne about 6,000 feet (1,800 m) down the 10,000-foot (3,000 m) runway.

The pilots were aware that the number one engine had failed, but could not have known it had separated from the plane, as the wings and engines were not visible from the cockpit and the control tower did not inform the flight crew of the problem. Investigators subsequently concluded the flight crew thought engine one had merely failed.

In addition to the engine’s failure, several related systems failed. The number one hydraulic system, powered by the number one engine, failed but continued to operate via motor pumps which mechanically connected it to hydraulic system three. Hydraulic system three was also damaged and began leaking fluid, but maintained pressure and operation up until impact. Hydraulic system two was undamaged. The number one electrical bus, whose generator was attached to the number one engine, failed causing several electrical systems to go offline, most notably the captain’s instruments, his stick shaker, and the slat disagreement sensors. While a switch in the overhead panel would have allowed the captain to restore power to his instruments, it was not used. It may have been possible for the flight engineer to reach the backup power switch (as part of an abnormal situation checklist – not as part of their take-off emergency procedure), in an effort to restore electrical power to the number one electrical bus. That would have worked only if electrical faults were no longer present in that number one electrical system. Furthermore, the flight engineer would have needed to rotate his seat, release his safety belt and stand up, to reach the switch. Since the plane never got higher than 350 feet (110 m) above ground, and was airborne for no more than 50 seconds, there wasn’t sufficient time to take such an action. In any event, the first officer was flying the airplane and his instruments continued to function normally.

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Witnesses observed the aircraft continue to climb to about 300 feet (91 m) above ground level while spewing a white vapor trail of fuel and hydraulic fluid. The first officer raised the nose up to 14 degrees to reduce the airspeed from 165 knots (306 km/h), to 153 knots (283 km/h), the speed specified in the emergency procedure for engine failure during takeoff. However, the engine separation had severed the hydraulic fluid lines that controlled the leading edge slats on the left wing, causing the slats outboard (towards the tip of the wing) of the separated engine to retract under air load. The retraction of the slats raised the stall speed of the left wing to approximately 159 knots (294 km/h), 6 knots (11 km/h) higher than the prescribed emergency speed. As a result, the left wing entered a full aerodynamic stall. The resulting asymmetric lift caused the plane to roll rapidly to the left and enter a steep dive from which it could not recover despite maximum opposite control inputs by the first officer. Flight 191 crashed in a 112-degree bank into an open field approximately 4,600 ft (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 and demolishing an old aircraft hangar at Ravenswood Airport that was used for storage. The fuselage cut a trench into the empty former airfield and the large amount of jet fuel generated a huge fireball.

The plume of smoke could be seen from the downtown Chicago Loop. The aircraft had disintegrated in the crash and explosion. There were some post-crash fires but they were very small as there were no large pieces of the aircraft left intact to burn. A fireman assisting at the scene of the crash later stated, “We didn’t see one body intact, just trunks, hands, arms, heads, and parts of legs. And we can’t tell whether they were male or female, or whether they were adult or child, because they were all charred.” Another first responder on the scene stated, “It was too hot to touch anybody and I really couldn’t tell if they were men or women. Bodies were scattered all over the field.”

DELTA FLIGHT 191

All 271 passengers and crew on board were killed instantly by the impact and subsequent explosion, making it the deadliest aviation accident in United States history. Two employees at a nearby repair garage were killed and two more severely burned. Of the 273 victims, only about a dozen bodies were found intact. Three additional residents were injured from falling aircraft debris. The airplane crashed in a field northwest of the intersection of Touhy Avenue (Illinois Route 72) and Mount Prospect Road on the border of Des Plaines and Mount Prospect, Illinois.

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