What happened
On July 19, 1989, United Airlines Flight 232, operating a McDonnell Douglas DC-10 with registration N110AA, was en route from Denver to Chicago O'Hare and then Philadelphia. The aircraft suffered a catastrophic failure of its tail-mounted engine due to an unnoticed manufacturing defect in the fan disk. This failure resulted in the loss of all flight controls.
The crew attempted to control the aircraft using differential thrust on the remaining engines. Despite their efforts, the plane crashed at Sioux Gateway Airport in Sioux City, Iowa. Of the 296 passengers and crew on board, 112 died during the accident, while 184 people survived. Thirteen passengers were uninjured.
Investigation
The investigation established that the crash was caused by a fatigue fracture in the fan disk of the tail-mounted engine. This defect allowed high-pressure air to leak into the hydraulic system, causing all three hydraulic systems to fail simultaneously. The crew's use of differential thrust was noted as an unprecedented attempt to control the aircraft.
Findings
Contributing factors included the manufacturing defect in the fan disk and the inability to maintain control without conventional flight controls. The accident highlighted the need for improved maintenance procedures and emergency response protocols.