1) improper maintenance—American Airlines had used a forklift shortcut to remove the engine and pylon together, rather than following McDonnell Douglas’s prescribed method
2) The detachment tore away part of the wing’s leading edge, rupturing hydraulic lines and severing electrical power to key systems, including the slat-position indicator and stall warning (stick shaker).
3) The pilots followed the standard engine-out procedure and reduced airspeed to V₂, which caused the aircraft to stall and roll uncontrollably left. This procedure was later found out to be incorrect.
Defective maintenance practices, inadequate oversight, vulnerabilities in DC-10 design, and unsafe training procedures combined to cause the crash, killing all 273 people on board and leading to sweeping reforms in airline maintenance and certification standards.
