Incident
The pilot was conducting an aerial filming operation when a bang was heard, accompanied by a loss of engine power. The helicopter was in a left-hand turn at 200 feet above ground level (agl) and 80 knots, heading in a southerly direction. The pilot entered an autorotation and maneuvered towards an open field. During descent, the pilot checked for engine power by pulling up on the collective and felt no power, but did not consult the engine instruments to verify the loss.
The pilot flared the helicopter and made a hard landing, after which the helicopter rolled over onto its right side.
Examination
Examination of the wreckage revealed evidence of driving torsional deformation in the forward short shaft, which drives the engine oil cooler and tail rotor. Flight control continuity was established. The fuel boost pump was energized and pumped 27 gallons of fuel to the airframe fuel filter, which was then deposited into a 50-gallon fuel drum. Magnetic chip detectors from the main transmission gearbox and tail rotor gearbox were removed and examined; no debris was found, and both transmissions operated smoothly.
Engine Testing
The engine was removed from the helicopter and installed in an instrumented test cell. Upon start, the engine produced 459 ft-lb of torque. It was then set to flight idle and subjected to a jam acceleration to maximum power. No surging or popping occurred during the acceleration, and turbine speeds and engine temperatures quickly stabilized. This test was repeated with similar results. The engine ran continuously in the test cell for 1 hour and 15 minutes.