Incident Overview
A flight instructor was conducting helicopter instructional flight training, during which the student performed hovering, straight-ahead, and 180-degree-turn autorotations. The instructor's remedial actions typically included adjustments to pitch attitude to maintain target airspeed or collective adjustments to keep rotor rpm within the normal operating range.
Sequence of Events
During an autorotation with a turn initiated by the student, the flight instructor took control of the helicopter. However, he allowed the rotor rpm to decay below the lower limit. He then adjusted the collective and throttle and initiated a decelerative flare in an attempt to build rotor rpm. Despite these inputs, the rotor rpm continued its decay. The flight instructor was unable to arrest the helicopter's descent.
Impact and Damage
The helicopter impacted the ground on the back of the skids, pitched forward, and rolled over. This resulted in substantial damage to the fuselage, tailboom, and both the main and tail rotor systems.
Mechanical Examination
No preexisting mechanical anomalies were noted with the helicopter.