What happened
During a cross-country training flight, the flight instructor closed the throttle at approximately 900 feet AGL to simulate an engine failure. During the subsequent autorotation, the engine RPM was not maintained at the 2500 RPM required by the pilot's operating handbook (POH).
The student pilot attempted to apply power during recovery at approximately 700 feet AGL, but failed to realize that the engine had actually stopped running. This caused the rotor RPM to deteriorate. The instructor took control of the helicopter at about 700 feet AGL and attempted to restart the engine. However, the student reported that the rotor RPM remained low throughout the descent. The aircraft subsequently impacted a large field. The student noted that during the final moments, the helicopter felt as though it had simply dropped the last few feet of the autorotation.
Findings
An investigation into the loss of engine power yielded no verified reason for why the engine stopped running. It was noted that the POH specifies that rotor RPM should be maintained during practice autorotations and explicitly states that engine restarts should not be attempted below 2000 feet AGL.