Key Safety Issue(s)

  • Failure of the fan disk resulted in liberation of debris in a pattern of distribution and with energy levels that exceeded the level of protection provided by the design features of the aircraft hydraulic systems. The three hydraulic systems, although physically isolated, were vulnerable to a single failure event due to their close proximity to on another, which compromised their independence (zonal hazard).

  • Inadequate consideration was given to the human factors limitation in inspection and quality control procedures for fluorescent penetrant inspection of the stage 1 fan disk at the UAL overhaul facility, which resulted in the failure to detect a fatigue crack.

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