Background
A flight instructor was conducting a practice autorotation with a private helicopter pilot under instruction (PUI). The purpose of the exercise was to demonstrate methods for reaching a suitable landing zone in the event of an engine failure over an area with limited landing options. The focus was on the glide phase with a power recovery before the need to flare.
The Maneuver
The instructor initiated the autorotation while the PUI observed, not on the controls. The instructor performed a series of S-turns: a right 90-degree turn, followed by a left 180-degree turn, and a final right 90-degree turn to return to the original heading. Throughout the maneuver, the rotor rpm remained within or above the green arc.
The Accident
During the last right 90-degree turn, the helicopter passed through an estimated 200 feet above ground level (agl). The instructor decided to discontinue the autorotation at that point due to insufficient airspeed (40 KIAS) and a higher than expected rate of descent, which resulted in a lower than anticipated height. During the time it took to make this decision, the helicopter descended to approximately 20-30 feet agl. The instructor initiated a flare and focused on keeping the skids level. However, the right skid contacted a dirt ledge about 6 feet higher than the intended landing zone surface. Following the skid impact, the helicopter pitched forward, and the nose struck the ground.
Findings
The pilot reported no mechanical failures or malfunctions at the time of the accident.