United Airlines Flight 232
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Template:Crash frame Template:Crash title Template:Crash infobox Template:Aircraft title Template:Aircraft infobox Template:End frame 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) suffered an uncontained failure of its number 2 engine in the tail, which destroyed all three of the aircraft's hydraulic systems. With no controls working except the throttles for the two remaining engines, it crashlanded 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 best-recognized air disasters in American aviation history, largely due to the presence of television crews near the air field as the plane landed end-over-end in a spectacular fireball.
Owing to the extraordinary skill of the crew and a DC-10 instructor pilot, 175 passengers and 10 crew members survived. The accident is considered one of the textbook examples of successful crew resource management, due to the excellent use of all the resources available aboard the plane and on the ground for help during the emergency.
The incident was made the subject of the 1992 television movie, "Crash Landing: The Rescue of Flight 232", and was also featured in an episode of Seconds From Disaster on the National Geographic Channel.
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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 and his flight crew soon realised that the initial failure 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 a continual tendency to turn to the right and was difficult to maintain on a stable course. Eventually the flight crew figured out that the only way to control the plane was by adjusting the thrust on the two remaining wing-mounted engines. At one point, Dennis E. Fitch, a DC-10 instructor who was deadheading as a passenger on the plane and was not part of the flight crew, offered his assistance. The task of flying the plane (using the throttles) was transferred to him. Meanwhile air-traffic control was contacted and an emergency landing at Sioux Gateway Airport organized. 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.
However, the root cause of the event lay in a metal 'inclusion' in the disk and was traced back to the metal processing plant from which the engine part was sourced from. It turned out that there was a process defect in place pertaining to the elimination of gaseous anomalies during the purifying process of the (molten) titanium disk ingot. These anomalies, if left unchecked, would contribute to a systematic decrease of the metals strength over time and ultimately, failure. Newer batches used a 'triple vacuum process' method to eliminate these impurities.
The resultant investigation and airworthines directive also revealed a handful of the titanium fan disks already in service from the same batch of ingots which had started to exhibit the intial symptoms of part failure (ie. crack propagation).
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.
Increased chances for survival
Of the 296 people aboard, 111 were killed or died as a result of the crash. However, 185 survived the incident. Captain Haynes later told of three contributing factors regarding the actual time of day that allowed for a better chance of survival:
1. The incident occurred during daylight hours;
2. The incident occurred as a shift change was occurring at both a regional trauma center and a regional burn center in Sioux City, allowing for more medical personnel to treat the injured; and
3. The incident occurred when the Iowa Air National Guard was on duty at Sioux Gateway Airport, allowing for 285 trained personnel to assist with triage and evacuation of the wounded.
1994 memorial
Commemorating the heroic rescue efforts shown by the Sioux City community after the crash, there is a statue that depicts Colonel Dennis Nielsen carrying a 3 year-old survivor Spencer Bailey to safety. The memorial is part of Sioux City's riverfront development located near the Anderson Dance Pavilion.
The memorial features contemplative areas and a tree-lined approach with plaques narrating the tragic event.
See also
Japan Airlines Flight 123 lost all hydraulic systems due to a structual failure. The resulting disaster killed 520 of the 524 people on board.
External links
- NTSB Report AAR-90/06 (pdf)
- Cockpit voice-recorder transcript (pdf)
- A talk given by the pilot, describing the crash, at NASA Dryden in 1991
- "Crash Landing: The Rescue of Flight 232" - TV movie
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