Accident Details
A helicopter was conducting a training flight with an instructor demonstrating a power-recovery autorotation to a dry river bed. The maneuver was initiated at 500 feet above ground level (AGL) by rolling off the throttle and lowering the collective pitch.
Sequence of Events
Approximately five seconds after beginning the autorotation, the instructor observed a change in sound and noticed the engine RPM had dropped to zero. The instructor continued the autorotation but overshot the soft gravel area of the river bed. The helicopter touched down in an area covered with large rocks.
Damage
Upon touchdown, the right skid fractured, and the main rotor struck and severed the tail boom. The helicopter subsequently came to rest on its right side.
The aircraft sustained substantial damage from the hard landing and subsequent rotor contact with the tail structure.