Incident Description
The pilot reported that he was practicing an auto-rotation. He stated that he moved the throttle to the idle position and lowered the collective. He then noticed a red light on the dashboard and heard the engine stop running. The pilot said that the subsequent auto-rotation concluded with a hard landing.
Investigation Details
The investigation at the scene verified that the flight controls and powerplant controls operated continuously and without interruption. Fuel was found in the helicopter's fuel tanks. A test run of the engine measured a low idle speed of 1,300 rpm.
Relevant Comment
A representative from a company that performs maintenance and rebuilding of helicopters similar to the accident helicopter commented that rapid reduction of the throttle combined with a low idle RPM setting could cause the engine to stop.
Flight Manual Instructions
The FAA-approved flight manual for the helicopter type instructs the pilot to "split the needles" by lowering the collective while keeping the throttle setting unchanged. According to the manual, this procedure results in a high idle RPM of about 2,500 rpm, which prevents the engine from loading up or stalling during the recovery phase.