Accident Sequence
The pilot reported that the helicopter's flight path was perpendicular to power lines ahead. During flight, a loud explosion was heard and the engine ceased operation. The pilot raised the collective control to clear the power lines, then lowered it. Prior to ground impact, the collective was raised again to cushion the landing. The helicopter struck the ground hard, bounced, touched down, rolled onto its left side, nosed over, and came to rest inverted. A small fire ensued but was extinguished by several individuals who responded to the scene.
Engine Examination
The engine was removed and sent to the manufacturer's facility for examination. Inspection revealed that a mounting boss on the air diffuser had failed due to fatigue. The line attached to that boss was identified as the interstage bleed air line. Additionally, a power turbine blade was found to have failed due to fatigue.
Maintenance History
Review of the engine logbooks disclosed that the engine had been removed from another helicopter and installed in the accident helicopter six days prior to the accident. Since installation, the engine had accumulated approximately 10 hours of operation. Total time since major overhaul was 703 hours. According to the engine daily inspection checklist, the air diffuser external vane brazements should be checked for cracks during inspections.