N74778Robinson Helicopter R22 BETA · 2005

The flight instructor reported that he was demonstrating a turning autorotation to his student. The instructor entered the glide, turned, and kept the engine and rotor RPM gauges in the green arc, while maintaining an airspeed of about 55 knots. He increased the throttle setting and raised the collective lever as the helicopter descended through 200 ft AGL, however, the rotor RPMs fell below the green arc. The instructor made the decision to continue the autorotation with ground contact and applied aft cyclic to reduce the decent rate. The helicopter landed hard and nosed over onto its right side, resulting in substantial damage to the tailboom and tail rotor assembly. The instructor reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.