NTSB Factual Report

After completing five or six successful simulated power-off autorotations, the pilot entered an autorotation in which he allowed the helicopter's descent rate to become excessive. Although he attempted to take corrective action, he did not do so in time to keep the aircraft from contacting an asphalt surface with sufficient force to result in substantial damage to the helicopter's airframe.

NTSB Probable Cause

An excessive descent rate during a simulated power-off autorotation, and the pilot's failure to initiate corrective action in time to keep the helicopter from impacting the terrain.