United 232 - Loss of All Flight Controls - Accident Prevention Vol. 48 No. 6

Oct 23, 2026

United Airlines Flight 232 suffered an almost uncontrollable crisis after a catastrophic engine failure caused the loss of all three redundant hydraulic flight control systems. The captain explains how luck, communications, preparation, execution, and cooperation helped the crew navigate to Sioux City and execute a crash landing shortly after hydraulic failure. The article frames five primary factors for coping with a one-in-a-billion inflight emergency and details the DC-10 flight-control system’s redundancy and mechanical operation.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

United 232: Coping With the “One-in-a-Billion” Loss of All Flight Controls

Accident overview and survival outcome

Key factors for coping: Luck

DC-10 flight control system and hydraulic redundancy

Why manual control was unavailable

F L I G H T S A F E TY F O U N D A T I O N Accident Prevention Vol. 48 No. 6 For Everyone Concerned with the Safety of Flight June 1991 | United 232: Coping With the “One-in-a-Billion”
Loss ofAll Flight Controls
The aircraft’s captain explains how well a flight crew handles a crisis in the air depending upon luck, communications, preparation, execution and cooperation. | | | --- | --- | | by
Capt. Alfred C. Haynes United Airlines | | | At 1516 hours on July 9, 1989, the author was captain of United Flight 232, a McDonnell Douglas DC-10-10. While cruising at 37,000 feet, the aircraft suffered a catastrophic engine failure. The uncontained disintegration of the number two engine’s fan rotor caused the loss of all three of the aircraft’s redundant hydraulic flight control systems and made the aircraft almost uncontrollable.
Capt. Haynes and his crew, augmented by a DC-10 instructor pilot who was aboard as a passenger, were able to navigate to the municipal airport at Sioux City, Iowa, U.S., where the aircraft was crash-landed approximately 45 minutes after the hydraulic failure. Of the 285 passengers and 11 crew members aboard, 174 passengers and 10 crew members survived.
That the aircraft was controlled at all and there were any survivors in this unusual circumstance was recognized by the industry as extraordinary airmanship by the crew. Among many other accolades, Capt. Haynes and his crew were awarded the Flight Safety Foundation President’s Special Commendation for Extraordinary Professionalism and Valor during the Foundation’s 42nd International Air Safety Seminar in Athens, Greece, during November 1989, the first formal international recognition of their accomplishment.
Capt. Haynes subsequently assembled his reflections on what happened during the ordeal along with input from a paper on the Sioux City area’s response to the disaster by | Michael T. Charles, Ph.D. The following is what he considers five primary factors involved in making it possible to cope with a major inflight emergency such as the one-in-a-billion loss of all flight controls.
Factor Number One Is Called Luck
There are five very important factors that contributed to the degree of success that occurred during the events that led to our landing at Sioux Gateway Airport: luck, communications, preparation, execution and cooperation.
The occurrence of good fortune may have differing connotations according to individual personal beliefs, but for this discussion we will call it luck. You could say we had bad luck in the form of an occurrence that, according to all the odds, could not be expected ever to happen. But we also had good luck, in that we were left with a chance to survive .
For instance, how did we get the aircraft to Sioux City to begin with, after the six-foot diameter fan on the number two engine (the center engine located on the vertical tail) failed? In less than one revolution, it instantaneously sprayed fan blades and pieces out through the right side of the engine housing, cutting a large gash in the forward edge of the horizontal stabilizer, separating a 12-by 10-foot cone section of the tail and peppering the horizontal stabilizer with more than 70 pieces of shrapnel. | The hydraulic lines of one of the three systems were torn out with the accessory section of the failed engine and the shrapnel from the disintegrated fan instantly severed the hydraulic lines of the remaining systems. The staggering import of that instantaneous and absolute occurrence can be better realized by an understanding of the workings of the flight control system on the DC-10 . In company with the Lockheed L-1011, Boeing 747, some military aircraft and others that are coming along, the DC-10 does not have cables running between the pilot’s control column and the control surfaces that, in jumbo jets, can involve extreme distances. Long cables can develop slack, can bind and require considerable attention to lubrication and main

FAQs

Flight 232遇到的核心故障是什么？

第二号发动机发生灾难性故障，导致三套冗余液压飞行控制系统全部失效，使飞机几乎无法操纵。

机组最终如何完成迫降？

机组结合沟通、准备、执行与协同等因素，在液压失效后仍成功将飞机引导至美国爱荷华州Sioux City的市政机场，并在液压失效约45分钟后完成着陆。

DC-10的飞行控制系统如何体现冗余设计？

DC-10没有从操纵柱直接连到操纵面的长电缆，而是通过液压管路分别驱动机翼和尾部执行机构；三套独立液压系统机械耦合电动泵，某一系统失压时可立即启动以恢复服务，并且不同控制面由不同系统分担执行。

Oct 23, 2026

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