What happened
A certificated flight instructor and a private pilot/commercial student were conducting a dual instructional flight in a helicopter to practice pinnacle approaches, landings, and takeoffs. The training was taking place near the top of a steep mountain ridge at approximately 3,600 feet MSL.
During the session, two initial approaches to the pinnacle landing zone were completed, resulting in one go-around and one successful landing. According to the instructor, the student had a tendency to allow the main rotor RPM to droop when adding power to terminate landing approaches.
On the third approach, the rotor RPM began to decrease again. The instructor pilot took control of the aircraft and attempted to recover from the low rotor RPM condition by increasing the throttle setting and decreasing collective pitch. Despite these efforts, the main rotor RPM continued to decline. The instructor attempted to land the helicopter at the edge of the ridge, but the aircraft slid backward over the edge of the mountain.
The helicopter tumbled 600 feet down the mountainside and began to break apart, during which a post-crash fire erupted. The instructor was ejected from the aircraft, while the student remained in the wreckage and sustained 1 fatal injury.