What happened
On May 25, 1979, American Airlines Flight 191, a McDonnell-Douglas DC-10-10, departed from Chicago-O'Hare International Airport bound for Los Angeles. The flight crew began the takeoff roll on runway 32R under clear weather conditions. During the acceleration phase, just prior to rotation, structural components of the number one engine pylon detached from the aircraft. Witnesses reported seeing white smoke or vapor near the left engine area.
As the pilot attempted to rotate the aircraft, the entire left engine and its pylon assembly separated from the wing, traveling over the top of the wing before falling onto the runway. The aircraft successfully lifted off approximately 6,000 feet down the runway and initially maintained a wings-level climb. However, shortly after reaching an altitude of 325 feet, the plane began to decelerate and entered a significant left roll. The aircraft continued this uncontrolled roll until it impacted an open field and a trailer park roughly 4,600 feet from the end of the runway. The impact, subsequent explosion, and fire resulted in 271 fatalities among the occupants and two fatal injuries to individuals on the ground.
Findings
The investigation determined that the primary cause was an asymmetrical stall and roll triggered by the uncommanded retraction of the left wing's outboard leading edge slats. This loss of aerodynamic symmetry was a direct result of unintended structural damage caused during maintenance. Specifically, when the engine and pylon were being reinstalled using a forklift to comply with service bulletins, the lack of precision in the maneuver led to damage on the pylon flange and wing clevis. The investigation also noted that the procedure used—removing the engine and pylon as a single unit—was not an approved method according to the maintenance manual, which had assumed separate removal.