United Airlines Flight 232 was a regularly scheduled United Airlines flight from Stapleton International Airport in Denver to O'Hare International Airport in Chicago, continuing to Philadelphia International Airport in Philadelphia, United States. On July 19, 1989, the McDonnell Douglas DC-10 serving the flight crash-landed at Sioux Gateway Airport in Sioux City, Iowa, after suffering a catastrophic failure of its tail-mounted engine due to an unnoticed manufacturing defect in the engine's fan disk, which resulted in the loss of all flight controls. Of the 296 passengers and crew on board, 112 died, while 184 people survived. Thirteen passengers were uninjured. Despite the fatalities, the accident is considered a good example of successful crew resource management, still a relatively new concept at the time. Contributing to the outcome was the crew's decision to recruit the assistance of a company check pilot, on board as a passenger, to assist controlling the aircraft and troubleshooting of the problem the crew was facing. A majority of those aboard survived; experienced test pilots in simulators were unable to reproduce a survivable landing. It has been termed "The Impossible Landing" as it is considered one of the most impressive landings performed in the history of aviation.
Aircraft The airplane, a McDonnell Douglas DC-10-10 (registration N1819U), was delivered in 1971 and owned by United Airlines since then. Before departure on the flight from Denver on July 19, 1989, the airplane had been operated for a total of 43,401 hours and 16,997 cycles (takeoff-landing pairs). The aircraft was equipped with three General Electric CF6-6D high-bypass turbofan engines produced by General Electric Aircraft Engines (GEAE). The aircraft's No. 2 (tail-mounted) engine had accumulated 42,436 hours and 16,899 cycles of operating time immediately prior to the accident flight. The DC-10 used three independent hydraulic systems, each powered by one of the aircraft's three engines, to power movement of the aircraft's flight controls. In the event of loss of engine power or primary pump failure, a ram air turbine could provide emergency electrical power for electrically powered auxiliary pumps. These systems were designed to be redundant, such that if two hydraulic systems were inoperable, the one remaining hydraulic system would still permit the full operation and control of the airplane. However, at least one hydraulic system must have fluid present and the ability to hold fluid pressure to control the aircraft. Like other widebody transport aircraft of the time, the DC-10 was not designed to revert to unassisted manual control in the event of total hydraulic failure. The DC-10's hydraulic system was designed and demonstrated to the Federal Aviation Administration (FAA) as compliant with regulations that "no single [engine] failure or malfunction or probable combination of failures will jeopardize the safe operation of the airplane..."
Crew Flight 232's captain, Al Haynes, 57, had been hired by United Airlines in 1956. He had 29,967 hours of total flight time with United, of which 7,190 were in the DC-10. Haynes' co-pilot was Bill Records, 48. He estimated that he had 20,000 hours of total flight time. He was hired first by National Airlines in 1969, and had worked for Pan American World Airways after that. He was hired by United in 1985, and had accrued 665 hours as a DC-10 first officer while at United. Flight engineer Dudley Dvorak, 51, was hired by United Airlines in 1986. He estimated that he had about 15,000 hours of total flying time. While working for United, he had accumulated 1,903 hours as a flight engineer in the Boeing 727 and 33 hours as a flight engineer in the DC-10. Denny Fitch, 46, was a training check pilot who was on Flight 232 as a passenger. He had studied the crash of Japan Air Lines Flight 123 which suffered a total hydraulic system failure and loss of flight controls, and he had practiced similar situations in a flight simulator. He was hired by United in 1968 and he estimated that, prior to working for United, he had accrued at least 1,400 hours of flight time with the Air National Guard, making his total flight time around 23,000 hours. His total DC-10 time with United was 2,987 hours, including 1,943 hours as a flight engineer, 965 hours as a first officer, and 79 hours as a captain. There were eight flight attendants on board.
Accident
Takeoff and engine failure Flight 232 departed from Stapleton International Airport in Denver at 14:09 Central Daylight Time, en route to O'Hare International Airport in Chicago with continuing service to Philadelphia. At 15:16, while the airplane was making a slight right turn at its cruising altitude of 37,000 feet (11,000 m), the fan disk of its tail-mounted General Electric CF6 engine disintegrated explosively. The uncontained failure resulted in the engine's fan disk departing the aircraft, tearing out components including parts of the No. 2 hydraulic system and supply hoses in the process; these were later found near Alta, Iowa. Engine debris penetrated the aircraft's tail section in numerous places, including the horizontal stabilizer, severing the No. 1 and No. 3 hydraulic system lines where they passed through the horizontal stabilizer. The pilots felt a jolt, and the autopilot disengaged. As First Officer Records took hold of his control column, Captain Haynes concentrated on the tail engine, the instruments for which indicated it was malfunctioning; he found its throttle and fuel supply controls jammed. At Dvorak's suggestion, a valve for fuel to the tail engine was shut off. This part of the emergency took 14 seconds.
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