The flight took off at 14:09 (CDT) from Stapleton International Airport, Denver, Colorado and was due to have flown to Philadelphia, Pennsylvania via Chicago, Illinois. At 15:16 the fan disk of its tail-mounted GE CF6-6 engine fragmented catastrophically and the engine assembly failed to contain the debris which severed all three of
the airplane's triply redundant hydraulic systems.
Captain Alfred C. Haynes accepted the assistance of pilot trainer Dennis E. Fitch who was travelling as a passenger. He and his flight crewe soon realised that the initial explosion had left all (sic) control surfaces on the airplane immovable. There was no conventional means of safely controlling the aircraft and it had an continual tendency to turn to
the right and was difficult to maintain on a stable course. Fitch was assigned to control the airplane by adjusting the thrust on the two remaining wing-mounted engines while air-traffic control was contacted and an emergency landing at Sioux Gateway Airport organised. Landing had originally been planned at the 8,999 foot Runway 31 but difficulties in controlling the aircraft left it with an approach on the shorter Runway 22 (6,600 foot) and with little capacity to maneuver.
Fitch continued to control the aircraft's descent by adjusting engine thrust. On final descent, the right wing dropped and the nose pitched forward. The tip of the right wing contacted the runway first and the aircraft skidded to the right, ignited and somersaulted.
In subsequent reconstructions of the circumstances of the accident in flight simulators, no pilot of any seniority has succeeded in reproducing Fitch's achievement of maneuvering the aircraft as far as the runway, generally losing control on mid air.
Investigation assigned the origin of the fracture of the fan disk to a failure of United Airlines maintance processes to detect an existing fatigue crack. The detection failure arose from poor attention to human factors in United Airlines' specification of maintenance processes.Narrative
Flightcrew performance
Causes