What happened
Prior to an instructional flight, the flight instructor and student pilot discussed procedures for managing a loss of engine power during takeoff. The student pilot, who had not previously performed this maneuver, believed the instructor would be performing a demonstration.
While climbing through 400 to 500 feet, the instructor notified the student of an impending simulated engine failure and reduced the throttle. This initiated an autorotation. During this phase, a misunderstanding occurred regarding who was controlling the aircraft: the instructor believed the student pilot had taken control, while the student pilot believed the instructor remained in control.
As the Robinson R22 (implied context of instructional flight/maneuver) appeared to be heading toward trees, the collective was raised to extend the glide. However, this caused the rotor rpm to decrease and forward airspeed to slow. Although the aircraft cleared the trees, the rotor rpm had fallen below the power-off range by the time the helicopter reached 60 feet above the ground. The instructor then took control, lowered the collective, applied throttle, and attempted to flare. Despite these actions, the helicopter continued its descent, the tail struck the ground, and the aircraft impacted the ground in a level attitude before rolling over. There were no injuries reported.
Findings
The investigation determined that during the autorotation, the rotor rpm decreased significantly due to the collective being raised to extend the glide, leaving the engine unable to recover power effectively at low altitude.