NTSB Factual Report

The certified flight instructor and his student were practicing a 180 degree autorotation with a power recovery to a hover, when the helicopter's sink rate increased dramatically in the flare about 40 feet above the ground. The flight instructor called for a go-around and increased power, raised the collective, and pushed the cyclic forward. The helicopter continued to descend and contacted the runway in a level attitude. After it came to a stop, a vibration was felt and the instructor confirmed that the main rotor blade had struck the tail boom. The instructor reported that there were no mechanical deficiencies with the helicopter.

NTSB Probable Cause

The flight instructor's failure to maintain control of the helicopter during a practice autorotation, which resulted in a hard landing.