Bell OH-58C N927SP accident near Jekyll Island, Georgia

Probable cause

The pilot's failure to maintain rotor rpm in the normal operating range during a practice autorotation, which resulted in a hard landing. Contributing to the accident was the inadequate supervision by the flight instructor.

NTSB analysis

As part of the training and evaluation flight, the pilot was demonstrating to the instructor a simulated engine failure and autorotation to touchdown with the engine throttle at the idle setting throughout the maneuver. At the termination of the maneuver, the pilot increased collective pitch to stretch the glide, and the rotor rpm was allowed to decay to the lower end of the normal operating range. He then "abruptly" flared the helicopter to slow its ground speed and added additional collective pitch to level the helicopter. The rotor rpm decayed further, the helicopter landed hard, and the main rotor struck the tailboom, severing the tail rotor driveshaft. Both pilots reported that there were no mechanical malfunctions or failures with the helicopter that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for ERA13TA237 for the full record.