1979 DC-10 crash in Chicago, US
American Airlines Flight 191 was a regularly scheduled domestic passenger flight from O'Hare International Airport in Chicago to Los Angeles International Airport. On the afternoon of May 25, 1979, the McDonnell Douglas DC-10 operating this flight was taking off from runway 32R at O'Hare International when its left engine detached from the wing, causing a loss of control. The aircraft crashed about from the end of runway 32R. All 271 occupants on board were killed on impact, along with two people on the ground. With a total of 273 fatalities, the disaster is the deadliest aviation accident to have occurred in the United States.
The National Transportation Safety Board (NTSB) found that as the aircraft was beginning its takeoff rotation, engine number one (the left engine) separated from the left wing, flipping over the top of the wing and landing on the runway. As the engine separated from the aircraft, it severed hydraulic lines that lock the wing's leading-edge slats in place and damaged a section of the left wing's leading edge. Aerodynamic forces acting on the wing resulted in an uncommanded retraction of the outboard slats. As the aircraft began to climb, the damaged left wing produced far less lift than the right wing, which had its slats still deployed and its engine providing full takeoff thrust. The disrupted and unbalanced aerodynamics of the aircraft caused it to roll abruptly to the left until it was partially inverted, reaching a bank angle of 112°, 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 structure holding the engine to the wing, caused by improper maintenance procedures at American Airlines.
Background.
Aircraft.
The aircraft involved was a McDonnell Douglas DC-10-10 registered as N110AA. At the time of the crash, it had logged just under 20,000 hours of flying time over seven years since it was delivered in 1972. The aircraft was powered by three General Electric CF6-6D engines. A review of the aircraft's flight logs and maintenance records showed that no mechanical discrepancies were noted for May 11, 1979. On the day of the accident, in violation of standard procedure, the records were not removed from the aircraft and were destroyed in the accident. The precautions toward making sure the plane was in a full working environment were not taken on the left wing's engine.76
Flight crew.
Captain Walter H. Lux (age 53) had been flying the DC-10 since its introduction eight years earlier. He had logged around 22,000 flying hours, of which about 3,000 were in a DC-10. He was also qualified to pilot 17 other aircraft, including the DC-6, DC-7, and Boeing 727.75 First Officer James Dillard (age 49) and Flight Engineer Alfred Udovich (age 56) were also highly experienced; they had 9,275 hours and 15,000 hours, respectively. Between them, they had 1,830 hours of flying experience in the DC-10.
Accident.
On the accident flight, during the takeoff rotation, the number-one engine 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.2 Robert Graham, supervisor of maintenance for American Airlines, stated:
 ;templatestyles src="Template:Blockquote/styles.css" / ;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 number-one engine pylon. I noticed that the number-one 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.
What was said in the cockpit in the 31 seconds leading up to the final impact is not known, as the cockpit voice recorder (CVR) 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 the first officer exclaiming, "Damn!", at which point the recording ends. This may also explain why air traffic controllers were 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 investigation, serving as a marker of exactly what circuit in the DC-10's extensive electrical system had failed.57
In addition, due to the loss of the engine, several related systems failed. The number-one hydraulic system, powered by the number-one engine failed, but continued to operate through 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 until impact. Hydraulic system two was undamaged. The number-one electrical bus, the generator of which was attached to the number-one engine, failed as well, causing several electrical systems to go offline, most notably the captain's instruments, his stick shaker, and the slat disagreement sensors. A switch in the overhead panel would have allowed the captain to restore power to his instruments, but it was not used. The flight engineer might have reached the backup power switch (as part of an abnormal situation checklist, not as part of their takeoff emergency procedure) 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. To reach that backup power switch, the flight engineer would have had to rotate his seat, release his safety belt, and stand up. (Which would be impossible since the aircraft banked extremely to the left) Regardless, the aircraft did not get any higher than above the ground and was only in the air for 31 seconds between the time the engine separated and the moment it crashed; there was insufficient time to perform such an action. In any event, the first officer was flying the airplane, and his instruments continued to function normally.52
The aircraft climbed to about above ground level while spewing a white mist trail of fuel and hydraulic fluid from the left wing. The first officer followed the flight director and raised the nose to 14°, which reduced the airspeed from to the takeoff safety airspeed (V2) of , the speed at which the aircraft could safely climb after sustaining an engine failure.
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 (immediately left of the number-one engine) to retract under air load. The retraction of the slats raised the stall speed of the left wing to about , higher than the prescribed takeoff safety airspeed (V2) of 153 knots. 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° bank angle with its right wing over its left wing. 
Since the cockpit had been equipped with a closed-circuit television camera positioned behind the captain's shoulder and connected to view screens in the passenger cabin, the passengers may have witnessed these events from the viewpoint of the cockpit as the aircraft dove towards the ground. Whether the camera's view was interrupted by the power loss from the number-one electrical bus is not known. The aircraft eventually slammed into a field around from the end of the runway.2 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 also crashed into an old storage hangar at the edge of the airport at the former site of Ravenswood Airport. The aircraft was destroyed by the impact force and ignition of a nearly full load of of fuel; no sizable components other than the engines and tail section remained.
The crash site is a field located 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.2
Victims.
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.
Nationalities of the victims.
Passengers.
Two of the victims in the crash of Flight 191 were:
Memorial.
For 32 years, the victims had no permanent memorial. Funding was obtained for a memorial in 2009 through a two-year effort by the sixth-grade class of Decatur Classical School in Chicago. The memorial, a concave wall with interlocking bricks displaying the names of the crash victims, was formally dedicated in a ceremony on October 15, 2011. The memorial is located on the south shore of Lake Opeka, at Lake Park at the northwest corner of Lee and Touhy Avenues, two miles east of the crash site. A remembrance ceremony was held at the memorial on May 25, 2019, the 40th anniversary of the accident.
Thirty victims whose remains were never identified are buried at Green Hills Memorial Park in Rancho Palos Verdes, California. The site of the crash was redeveloped around March 2021, and has been named the future site of an interchange for Interstate 90.
Investigation.
The disaster and investigation received widespread media coverage. The impact on the public was increased by the dramatic effect of an amateur photo taken of the aircraft rolling that was published on the front page of the "Chicago Tribune" on the Sunday two days after the crash. 
Engine separation.
Witnesses to the crash were in universal agreement that the aircraft had not struck any foreign objects on the runway. In addition, no pieces of the wing or other aircraft components were found along with the separated engine, other than its supporting pylon; this led investigators to conclude that nothing else had broken free from the airframe and struck the engine. Hence, the engine/pylon assembly separation could only have resulted from a structural failure. The cockpit instrument panels were damaged so badly that they did not provide any useful information.
During the investigation, an examination of the pylon attachment points revealed some damage done to the wing's pylon mounting bracket that matched the bent shape of the pylon's rear attachment fitting. This meant that the pylon attachment fitting had struck the mounting bracket at some point. This was important evidence, as the only way the pylon fitting could strike the wing's mounting bracket in the observed manner was if the bolts that held the pylon to the wing had been removed, and the engine/pylon assembly was supported by something other than the aircraft itself. Therefore, investigators could now conclude that the observed damage to the rear pylon mount had been present before the crash occurred rather than being caused by it.18
The NTSB 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, 1979.68 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, as well as Continental Airlines and United Airlines, had developed a different procedure that saved about 200 working hours per aircraft and "more importantly from a safety standpoint, it would reduce the number of disconnects (of systems such as hydraulic and fuel lines, electrical cables, and wiring) from 79 to 27."26 This new procedure involved the removal of the engine and pylon assembly as a single unit rather than as individual components. United's implementation involved the use of an overhead crane to support the engine/pylon assembly during removal