Accident Sequence
During an instructional flight, a certified flight instructor (CFI) was demonstrating a 180-degree autorotation to a pilot-rated student. The CFI positioned the helicopter on a downwind leg, abeam the intended landing site, at an altitude of about 800 feet above ground and an airspeed of about 70 knots. He then initiated a right-turning autorotation.
After the helicopter had turned approximately 80 degrees, the pilot-rated student commented that the approach appeared to be landing short. In response, the CFI increased the rate of turn. Near the end of the turn, the CFI observed that the rotor RPM was starting to decay, and he applied down collective pitch.
As the helicopter rolled out of the turn, it seemed to be descending faster than it was moving forward. The CFI began a cyclic flare to reduce the descent rate, but the helicopter impacted the ground hard and rolled onto its left side.
Damage
The helicopter sustained substantial damage to the tailboom and fuselage structure.
Instructor Report
The CFI reported that there were no mechanical malfunctions or failures that would have precluded normal operations.