Precursors

At the time of the Pensacola accident, there was an industry wide initiative underway for the purpose of studying causes of turbine engine uncontained failures, and identifying areas where improvements could be made. This initiative led to the development of the Aerospace Industry Association Rotor Manufacturing Subcommittee Lessons Learned Database to identify safety precursors associated with turbine engines.

Other engine manufacturers have also experienced rotor failures associated with abusive machining of hub and disc bolt holes. Examples of some of these failures include:

  • JT8D-7B engine fan hub uncontained fracture on Pan American World Airways 727 on takeoff in Miami on February 17, 1982. The titanium fan hub failed due to fatigue cracking initiating from an area of abusive machining.
  • CF6-6 engine fan hub uncontained fracture on United Airlines DC-10, Sioux City, Iowa on July 19, 1989. The titanium fan hub failed due to fatigue cracking initiating from a Type I hard alpha metallurgical defect on the surface of the fan hub bore.
  • CF6-50C2 engine HPC stage 3-9 spool uncontained fracture on an Egypt Air A300-B4 during takeoff roll in Cairo, Egypt in 1995. The stage 6 portion failed due to fatigue cracking initiating from a nitrogen stabilized hard alpha inclusion located on the aft side of the disk web.

At the time the accident hub was produced, the JT8D-219 fan hub scrap rate at Volvo was approximately 11%. This was considered by investigators to be an extremely high scrap rate. In addition, it was learned that Volvo had introduced 12 process changes to the hole drilling operation.

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