The NTSB determined that the probable cause of this accident was the inadequate consideration given to human factors, and limitations in the inspection and quality control procedures used by United Airlines' engine overhaul facility. These resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the titanium-alloy stage-1 fan disk that was manufactured by General Electric Aircraft Engines. The uncontained manner in which the engine failed resulted in high-speed metal fragments being hurled from the engine; these fragments penetrated the hydraulic lines of all three independent hydraulic systems on board the aircraft, which rapidly lost their hydraulic fluid. The subsequent catastrophic disintegration of the disk resulted in the liberation of debris in a pattern of distribution and with energy levels that exceeded the level of protection provided by design features of the hydraulic systems that operate the DC-10's flight controls; the flight crew lost its ability to operate nearly all of them.
Captain Sim L1011 Crack 38
The manufacturing process for titanium was changed to eliminate the type of gaseous anomaly that served as the starting point for the crack. Newer batches of titanium use much higher melting temperatures and a "triple vacuum" process in an attempt to eliminate such impurities (triple melt VAR).[28][29]
The accident has since become a prime example of successful crew resource management (CRM).[38][26] For much of aviation's history, the captain was considered the final authority, and crews were to respect the captain's expertise without question. This began to change in the 1970s, especially after the 1978 United Airlines Flight 173 crash in Portland, Oregon, and the Tenerife airport disaster. CRM, while still considering the captain as final authority, instructs crew members to speak up when they detect a problem, and instructs captains to listen to crew concerns. United Airlines instituted a CRM class in the early 1980s. The NTSB later credited this training as valuable toward the success of United 232's crew in handling their emergency.[1] The FAA made CRM mandatory in the aftermath of the accident. 2ff7e9595c
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