On June 8, 1999, a Hughes 369D (registration N8306F) was involved in an aviation accident near Southbend, WA. Investigators recorded the probable cause as: The compressor impeller disc failed due to the propagation of fatigue cracks that initiated in corrosion pits on the aft face of the disc, with corrosion attributed to environmental exposure. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced a complete power loss after releasing an external load, leading to a hard landing. Investigation revealed a compressor impeller disc failure from fatigue cracks originating in corrosion pits.
Accident Sequence
After releasing an external load, the pilot applied power to climb away. A puff of smoke emitted from the engine, followed by a complete loss of power. The helicopter began spinning left and descending rapidly. The pilot attempted an autorotation in a confined area, but the aircraft impacted the ground with sufficient force to sustain substantial damage.
Engine Examination
A teardown inspection of the engine revealed that a three-inch section of the compressor impeller disc had separated, leading to total engine failure.
Metallurgical Findings
Metallurgical examination of the impeller determined that the disc failed due to the propagation of fatigue cracks that initiated in corrosion pits on the aft face of the disc. According to the metallurgist, the corrosion was due to exposure to environmental elements and not due to repetitive cyclic operation.
Probable cause
The compressor impeller disc failed due to the propagation of fatigue cracks that initiated in corrosion pits on the aft face of the disc, with corrosion attributed to environmental exposure.