What happened
During an instructional flight, a flight instructor and a commercial pilot student were performing 180-degree autorotations. These maneuvers were intended to be terminated into a hover by adding engine power.
On the first attempt, the student flared at a high altitude. During the recovery phase, rotor speed decayed, necessitating an emergency landing on the taxiway. The instructor subsequently instructed the student to increase engine power in conjunction with increasing the collective to maintain necessary rotor speed.
During the second autorotation, the student performed a lower and more aggressive flare. As the student increased the collective, the rotor speed decreased once again. The instructor reported that as the collective continued upward, both the engine and rotor speed decreased. The instructor intervened on the controls, increasing the collective and throttle while attempting to level the aircraft, at which point the tail rotor struck the taxiway. Following the impact, the instructor noted an airframe vibration and landed the helicopter.
Findings
The helicopter sustained substantial damage. Both occupants were not injured. There were no reported mechanical malfunctions or failures prior to the accident.