Why Planes Crash: Breaking Point

American Airlines Flight 191 was a regularly scheduled passenger flight from O'Hare International Airport in Chicago to Los Angeles International Airport. The McDonnell Douglas DC-10-10 crashed on May 25, 1979, moments after takeoff from Chicago. All 258 passengers and 13 crew on board were killed, along with two people on the ground. It is the deadliest aviation accident to have occurred in the United States. Investigators found that as the jet was beginning its takeoff rotation, engine number one on the left wing separated and flipped over the top of the wing. As the engine separated from the aircraft, it severed hydraulic fluid lines that locked the wing leading edge slats in place, and it damaged a three-foot section of the left wing's leading edge. Air loads on the wing resulted in an uncommanded retraction of the outboard slats. As the jet attempted to climb, the left wing stalled while the right wing, with its slats still deployed, continued to produce lift. The jetliner subsequently rolled to the left until it was partially inverted, reaching a bank angle of 112 degrees, before crashing in an open field by 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. The faulty procedure was banned, and the aircraft type went on to have a long passenger career. It has since found a second career as a cargo airplane.The weather was clear, with a northeast wind at 22 knots (41 km/h). At 2:50 CDT, Flight 191 pushed back from gate K5 and was cleared to taxi to runway 32R/14L. Maintenance crews present at the gate did not notice anything unusual during pushback, engine start, or taxi.[5] Everything looked normal as the flight began its takeoff roll at 3:02.[6] Just as the aircraft hit takeoff speed, the number one engine and its pylon assembly separated from the left wing, ripping away a 3-foot (0.91 m) section of the leading edge with it. The combined unit flipped over the top of the wing and landed on the runway.[7] Robert Graham, supervisor of maintenance for American Airlines, stated: "As the aircraft got closer, I noticed what appeared to be vapor or smoke of some type coming from the leading edge of the wing and the No. 1 engine pylon. I noticed that the No. 1 engine was bouncing up and down quite a bit and just about the time the aircraft got opposite my position and started rotation, the engine came off, went up over the top of the wing, and rolled back down onto the runway... Before going over the wing, the engine went forward and up just as if it had lift and was actually climbing. It didn't strike the top of the wing on its way, rather it followed the clear path of the airflow of the wing, up and over the top of it, then down below the tail. The aircraft continued a fairly normal climb until it started a turn to the left. And at that point, I thought he was going to come back to the airport."[8] It is not known what was said in the cockpit in the 50 seconds leading up to final impact, as the cockpit voice recorder lost power when the engine detached. The only crash-related audio collected by the recorder is a thumping noise (likely the sound of the engine separating) followed by First Officer Dillard exclaiming "Damn!", at which point the recording ends. This may also explain why Air Traffic Control was unsuccessful in their attempts to radio the crew and inform them that they had lost an engine. This loss of power did, however, prove useful in the subsequent investigation, serving as a marker of exactly what circuit in the DC-10's labyrinthine electrical system had failed.[7] 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 that 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 might 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 the number one electrical system. Furthermore, to reach the switch the flight engineer would have needed to rotate his seat, release his safety belt, and stand up. Since the aircraft never got higher than 350 feet (110 m) above ground, and was in the air for only 50 seconds between when the engine separated and when it crashed, there was not sufficient time to take such an action. In any event, the first officer was flying the airplane and his instruments continued to function normally.[7] As the wings and engines were not visible from the cockpit, the crew likely had no idea that an engine had fallen off, only that one had failed. Since it was no longer possible to abort the takeoff at this point, the crew followed the standard operating procedure for an "engine out" climb. This procedure is to climb at the takeoff safety airspeed (V2) and attitude (angle), as directed by the flight director. The partial electrical power failure (produced by the separation of the left No. 1 engine) meant that neither the stall warning or slat retraction indicator were operative. The crew were therefore unaware that the slats on the left wing were retracting, this retraction significantly raised the stall speed of the left wing. By following the takeoff safety airspeed, the left wing stalled while right wing was still producing lift, the aircraft banked sharply to the left uncontrollably. Later, in simulator recreations of the accident it was determined that by climbing at a higher airspeed the crash could have been averted.[7] The aircraft climbed to about 325 feet (99 m) above ground level while spewing a white mist trail of fuel and hydraulic fluid from the left wing.The first officer had followed the flight director and raised the nose to 14 degrees which reduced the airspeed from 165 knots (306 km/h) to the takeoff safety airspeed (V2) of 153 knots (283 km/h), the speed at which the aircraft could safely climb after sustaining an engine failure.[7] However, the engine separation had severed the hydraulic fluid lines that controlled the leading edge slats on the left wing and locked them in place, causing the outboard slats (immediately left of the No. 1 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 takeoff safety airspeed (V2) of 153 knots (283 km/h). As a result, the left wing entered a full aerodynamic stall. At 325 feet (99 m) above ground level, the resulting asymmetric lift caused the aircraft to commence rolling rapidly to the left and to enter a steep dive from which it could not recover despite maximum opposite control inputs by the first officer. The aircraft continued rolling until it was partially inverted at a 112 degree bank angle, right-wing over left wing. It then slammed into a field approximately 4,600 ft (1,400 m) from the end of the runway.[7] 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 Airport, which was used for storage.[9] The nearly full fuel load ignited in a huge fireball almost immediately. The aircraft was almost completely destroyed, with no significant pieces of the fuselage remaining. The only sizable components left were the landing gear, the two engines that were still attached to the aircraft at impact, the engine that separated from the aircraft, and the tail section.[7] 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."[9] 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."[9] In addition to the 271 people on board the aircraft, two employees at a nearby repair garage were killed and two more severely burned. At 273 victims, this was the deadliest accident in US aviation history.[note 1][10] Of the victims, only about a dozen bodies were found intact.[9] Three additional residents were injured from falling aircraft debris. The crash scene was in a field northwest of the intersection of Touhy Avenue (Illinois Route 72) and Mount Prospect Road on the border of the suburbs of Des Plaines and Mount Prospect, Illinois.[7]