What happened
A police pilot was conducting a right-hand orbit at approximately 500 feet when he heard a loud 'clunk' followed by an immediate loss of engine power. Due to the sudden failure, the pilot initiated an autorotation over an urban area. During the descent, the helicopter struck a tree and subsequently collided with the terrain.
The investigation
Post-accident examination of the wreckage identified that the #4 connecting rod was protruding from the engine case. Investigators found that the connecting rod bolts had been stretched beyond the limits specified by the manufacturer. Additionally, valve tappets with incorrect part numbers were found installed in the engine.
Further review of the engine records showed that the engine had undergone an overhaul by T.W.Smith Engine Company Inc. approximately 500 flight hours before the accident. The documentation for this overhaul indicated that maintenance and inspections had been performed on components that were not actually installed on the engine involved in the accident, as well as on parts that were supposed to be discarded and replaced.
Detailed examination of the fractured #4 connecting rod revealed galling spots at the fatigue origin areas, along with crack arrest positions and ratchet marks that indicated the progression of a fatigue crack.