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Significant Factors

Summary

  1. Most VSV arm pin retaining flare diameters recorded during the engine disassembly were less than the minimum dimensional limit specified in the engine manufacturer's manual.
  2. Two 6th stage VSV arm pins were missing from the synchronizing ring at the 10 o'clock and 12 o'clock positions.
  3. Four other vane arm pins were loose in the synchronizing ring.
  4. The 6th stage HPC blade failed due to high cyclic stress of the blade in turbulent airflow created by off-schedule stator vane angle.
  5. Maintenance actions in accordance with prescribed procedures for VSV arm pin flaring and a published service bulletin, specifically designed to address VSV synchronizing ring pin security via a tack weld process, failed to prevent pin loss.
 
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