Incident Overview
A helicopter was substantially damaged when its tail rotor contacted the taxiway during recovery from an intentional autorotation. The flight instructor and the commercial pilot serving as a dual student were not injured. The flight instructor reported that the instructional flight involved 180-degree autorotations, which were to be terminated into a hover with the addition of engine power.
Sequence of Events
According to the flight instructor, during the first autorotation, the dual student flared high. As the recovery began, rotor speed decayed, requiring a landing on the taxiway. The instructor then directed the student to increase engine power as collective was raised during recovery to maintain rotor speed.
On the second autorotation, the instructor stated that the dual student flared lower and "a little more aggressively." As the student increased collective, rotor speed again decayed. The flight instructor noted that "as the collective continued upward the engine and rotor [speed] decreased." He intervened on the controls, continuing to increase collective and throttle while leveling the aircraft. During this intervention, the tail struck the taxiway.
Aftermath
The flight instructor subsequently landed the helicopter after noticing an airframe vibration. He reported no malfunctions or failures prior to the accident. The helicopter sustained substantial damage to its tail rotor and likely other components.
Findings
No official probable cause was stated. The flight instructor's account indicates that rotor speed decay occurred during both autorotation recoveries, leading to the tail strike on the second attempt.