Incident Summary
During an instructional flight, the instructor pilot directed the student to reduce the throttle to idle to simulate an engine failure. After the throttle reduction, the instructor realized that the engine had actually failed. A power-off autorotation was executed to a grass field with a slight upslope, into the wind. During the landing, the helicopter slid backward approximately 15 feet. The tail boom flexed upward and was struck by the main rotor.
Damage
The helicopter sustained damage to the tail boom, all three main rotor blades, and the tail rotor drive shaft.
Investigation Findings
A subsequent engine run, overseen by two FAA inspectors, revealed no anomalies that would have precluded normal operations. The inspectors noted that the idle RPM and idle mixture were adjusted poorly for altitude and temperature, but this did not cause the loss of engine power. The loss of power was attributed to the instructor pilot's failure to follow the cautions in the helicopter's flight manual.