United Airlines Flight 232
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United Airlines flight 232 "UA232", "UAL232" (United 232 Heavy) was a scheduled flight operated by United Airlines. On July 19, 1989, its Douglas DC-10-10 (Registration N1819U) crashed on the runway at Sioux City, Iowa, killing 110 of its 285 passengers and one of the 11 crew members. It is one of the most famous crashes in American aviation history, largely due to the presence of television film crews near the air field as the plane attempted to land.
Owing to the extraordinary skill of the crew and a deadheading DC-10 instructor pilot, Dennis E. Fitch, 175 passengers and 10 crew members survived. The accident is considered one of the classical examples of successful CRM, owing to the excellent use of all the resources available aboard the plane and on the ground for help during the emergency.
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Narrative
The flight took off at 14:09 (CDT) from Stapleton International Airport, Denver, Colorado and was due to have flown to Philadelphia International Airport in Philadelphia, Pennsylvania via O'Hare International Airport in 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 senior training pilot and DC-10 expert Dennis E. Fitch, who was travelling as a passenger. He and his flight crew soon realised that the initial explosion had left all control surfaces on the airplane immovable. As the triple failure of the hydraulic systems had been considered impossible by the aircraft engineers, 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 (2743 m) Runway 31. Difficulties in controlling the aircraft left it with an approach on the shorter Runway 22 of 6,600 feet (2012 m) 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.
Flightcrew performance
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 in mid air.
Because this type of aircraft control is difficult for humans to achieve, some researchers have attempted to integrate this control ability into computers, especially those in fly-by-wire aircraft. Early attempts to add the ability to real planes were not very successful, based on experiments conducted in flight simulators where jet engines are usually modeled as "perfect" devices with exactly the same thrust on each engine. Later, programming was updated to compensate for the problem, and planes have been successfully flown with this software installed. However, it remains a rarity on commercial aircraft.
Causes
Investigation assigned the origin of the fracture of the fan disk to a failure of United Airlines maintenance processes to detect an existing fatigue crack. The detection failure arose from poor attention to human factors in United Airlines' specification of maintenance processes.
Some portions of the plane that broke away when the fan disk failed were later found in farm fields along the flight path.
Following the accident, other planes were modified to incorporate additional backup means of manipulating some of the flight controls even if the three hydraulic systems fail.
External links
- NTSB Report AAR-90/06 (pdf) (http://amelia.db.erau.edu/reports/ntsb/aar/AAR90-06.pdf)
- Cockpit voice-recorder transcript (pdf) (http://aviation-safety.net/investigation/cvr/transcripts/cvr_ua232.pdf)
- Cockpit voice-recorder recording at time of impact (http://www.airdisaster.com/download2/ual232.shtml)
- Accident photos (http://www.airdisaster.com/photos/ua232/photo.shtml)
- A talk given by the pilot, describing the crash, at NASA Dryden in 1991 (http://yarchive.net/air/airliners/dc10_sioux_city.html)