American Airlines Flight 191 — An Engine Tore Off on Takeoff, and a Wing Stalled

On 25 May 1979, American Airlines Flight 191, a McDonnell Douglas DC-10-10 registered N110AA, crashed seconds after takeoff from Chicago O’Hare International Airport, killing all 271 people aboard and two more on the ground, for a total of 273. It remains the deadliest aviation accident on United States soil. As the aircraft rotated for takeoff on a routine service to Los Angeles, the No. 1 engine — the left wing engine — together with its supporting pylon broke away from the wing, flipped up and back over the wing’s leading edge, and fell to the runway. The aircraft, already committed to flight, climbed briefly, then rolled steeply to the left, descended, and struck the ground in an open field near a trailer park about a kilometre beyond the runway, where it disintegrated and burned. The whole sequence, from the engine departing the wing to impact, lasted only about 31 seconds.

The engine separation alone would not necessarily have been fatal — the DC-10 was designed to fly on two engines. What made the loss unrecoverable was a cascade of secondary failures caused by the engine and pylon tearing away. As the pylon ripped from the wing it severed hydraulic and electrical lines in the leading edge. This caused the outboard leading-edge slats on the left wing to retract, while those on the right wing stayed extended. The wing with retracted slats stalled at a higher speed than the other; with one wing flying and one stalled, the aircraft rolled uncontrollably to the left. The same damage disabled the cockpit instruments that would have warned the crew of the slat asymmetry and the impending stall, so the pilots, who could not see their own wings from the cockpit, flew the aircraft by the book for an engine-out climb — exactly the procedure that, with the left slats retracted, drove the dying wing into a deeper stall.

The National Transportation Safety Board investigated. Its report, AAR-79-17, determined that the engine and pylon had separated because of damage inflicted weeks earlier during maintenance. American Airlines, like some other carriers, had adopted a time-saving procedure to remove and reinstall the engine and pylon as a single unit using a forklift, rather than detaching the engine from the pylon first. The procedure was difficult to perform precisely; on N110AA a misalignment during reinstallation had cracked the pylon’s aft attachment fitting, and that crack grew under flight loads until the pylon failed on takeoff. The Board’s verdict was a maintenance-induced structural failure compounded by design vulnerabilities and oversight gaps. The accident grounded the entire DC-10 fleet for weeks and reshaped how engine maintenance procedures are approved and policed.