Accident Sequence
The pilot was maneuvering the helicopter in a right-hand orbit at an altitude of approximately 500 feet. A loud 'clunk' was heard, immediately followed by a loss of engine power. The pilot initiated an autorotation over an urban area. During the descent, the helicopter struck a tree and then collided with terrain.
Wreckage Examination
Post-accident inspection of the wreckage revealed the number 4 connecting rod protruding from the engine case. The connecting rod bolts had been stretched beyond the manufacturer's specified limits. Additionally, valve tappets with incorrect part numbers were installed in the engine.
Maintenance History
Review of the engine records indicated that the engine had been overhauled by T.W. Smith Engine Company Inc. approximately 500 flight hours before the accident. The overhaul documentation included maintenance and inspections performed on components that were not installed on the accident engine and on parts that were designated to be discarded and replaced.
Connecting Rod Analysis
Examination of the fractured number 4 connecting rod showed crack arrest positions and ratchet marks, which are indicative of fatigue crack progression. Galling spots were found on the fatigue origin areas.