What happened
The helicopter was operating with a certified flight instructor (CFI) and owner in the right seat and a student pilot in the left seat. While flying over high terrain at approximately 70 miles per hour, the student reported a gradual loss of power. The CFI assumed control and attempted to effect an airstart, but this effort was unsuccessful. The pilot then tried to arrest the descent, but the aircraft impacted the ground with such force that it broke up. Both skids collapsed, and the tail boom and rotor separated at approximately the 180 station, located about 25 feet from the main wreckage.
The investigation
An inspection of the aircraft and engine revealed significant mechanical issues. One magneto was found to be off its timing and had lost approximately 43% of its magnetism. Additionally, both magnetos contained oil and showed signs of carbon brush wear. Dual controls were installed in the helicopter, except on the right side where there were no torque pedals attached to the torque control stubs.
Findings
The investigation determined that the engine failure was caused by a magneto that was off timing and had lost magnetism. The presence of oil and carbon brush wear in both magnetos contributed to the loss of power. The pilot's inability to restart the engine resulted in the crash.