Incident
A helicopter performing a hover at approximately 75 feet above ground level, awaiting ground personnel to attach a line to its external sling load, experienced a sudden loss of engine power. The pilot reported that the engine decelerated to flight idle and could not be restarted. He initiated an autorotation but noted that rotor RPM had decayed, resulting in a hard landing.
Post-Accident Findings
After the accident, the pilot discovered the PY accumulator from the engine governor lying on the ground a short distance from the helicopter. The pilot subsequently started the engine, which ran adequately but would not accelerate above 30 percent power. Investigation revealed that the Allison 250 turbine engine will operate at only approximately 30 percent of its rated RPM without the PY accumulator installed.
Maintenance Context
The pilot stated that the PY accumulator and related parts had been reinstalled on the helicopter after removal for maintenance only two and a half hours prior to the accident. The pilot expressed the opinion that the accumulator should be safety-attached to preclude separation due to vibration.