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.