Incident Overview
A flight instructor (CFI) was demonstrating a hovering autorotation to a dual student. Before initiating the maneuver, the CFI did not verify that the landing surface was hard packed and not soft. The helicopter descended to a skid height of approximately 3 to 5 feet above the ground, at which point the CFI closed the throttle and performed a straight-ahead landing.
Sequence of Events
Upon touchdown, the helicopter's landing skids slid approximately 5 feet before encountering the soft terrain. The skids dug into the ground, causing the helicopter to nose down. The force of the nosing-over motion brought the main rotor blades into contact with the tailboom assembly, severing it completely.
Conclusion
The accident occurred because the CFI failed to ensure that the landing surface was adequately compacted to support the helicopter during the hovering autorotation. No other causal factors were identified in the source material.