Incident Overview
A helicopter flight instructor was preparing a helicopter-rated commercial pilot for a flight instructor check ride. During the training session, the pilot receiving instruction completed a straight-in autorotation. Subsequently, the flight instructor demonstrated a throttle-off, 180-degree autorotation from an altitude of 600 feet above ground level (AGL).
Maneuver Attempt
The pilot receiving instruction then attempted the same autorotation maneuver. During the entry, the helicopter's airspeed became slow while the rotor rpm remained within the normal range ("in the green"). The pilot receiving instruction lowered the nose of the helicopter, which increased airspeed. As the helicopter turned onto final approach at an altitude of about 300 feet AGL, the flight instructor advised the pilot to ease back on the cyclic while raising the collective to maintain rotor rpm.
Instructor Intervention
At approximately 150 feet AGL, with an airspeed of about 85 knots and a rate of descent of about 2,000 feet per minute, the flight instructor took control of the helicopter and began pulling back on the cyclic while raising the collective. Despite these inputs, the helicopter continued a tail-low descent into the ground, resulting in the tail boom being severed.
Postaccident Examination
A postaccident examination revealed no preexisting mechanical malfunctions or anomalies that would have precluded normal operation of the helicopter.