Computer-Related Incidents with Commercial Aircraft

The American Airlines DC10 Takeoff Accident in Chicago

25 May 1979 Synopsis At about 3pm CDT, AA Flight 191 took off from O'Hare's runway 32R in clear weather and fifteen miles visibility. During the takeoff rotation, the left engine and pylon assembly and a part of the leading edge of the left wing fell off. Climb continued until about 325ft altitude, when the aircraft rolled left inverted, the nose fell through and the aircraft impacted into open ground 4,600ft northwest of the departure end of the runway. The separation of the engine and pylon severed hydraulic lines, causing the high-lift devices (slats) on the leading edge to retract uncommanded. The slat position indicating system in the cockpit was inoperative, and the crew had no means of visually inspecting the state of the left wing during takeoff procedures. They apparently flew the takeoff according to recommended procedures, which specified a climb speed below the stall speed of the left wing with slats retracted. The left wing stalled and the roll began. Although the aircraft had no digital automation to speak of, the accident highlights both common-mode problems and human-interface issues, both important contributors to computer-related aircraft accidents. The initiating event was the separation of the engine and pylon and retraction of leading-edge slats due to the number 3 hydraulic lines being severed. However, the aircraft remained flyable - had the crew known. But the devices informing the crew of the aircraft's condition also failed due to the same event. We include the NTSB Aircraft Accident Report of December 21, 1979, the final report.