The aircraft was cruising at 2000 feet above mean sea level, when the pilot observed an apparent engine failure. The pilot set the aircraft up for an autorotational approach. As the aircraft approached the ground, the pilot observed that the surface was not suitable for a run-on landing so he modified the approach, just prior to touchdown, so that the aircraft would land with zero residual forward speed. The touch-down was heavier than normal and the main rotor severed the tail boom. After landing the pilot observed that the engine was still running, but at a speed well below ground idle, and it had to be shut down manually. The engine lost power because the body of the power turbine governor failed as a result of high cycle, low stress fatigue cracking. The precise reason for the start of the fatigue crack could not be determined. However, it is likely that it was caused by the additional stress placed on the governor body when the vibration of an unrestrained servo pressure accumulator was transmitted to the body by the rigid stainless steel piping. The stress may have been aggravated by contact between the accumulator and an undetermined part of the aircraft.
