Bell 47G 3B N347BH accident near Custer, South Dakota

Probable cause

The pilot’s mismanagement of rotor RPM and subsequent forced landing on uneven terrain which led to a dynamic rollover.

NTSB analysis

The commercial-rated pilot and flight instructor were completing familiarization training in the accident helicopter. After successful training flights the morning of the accident, the flight instructor decided to remove the dual controls from the helicopter, and one additional passenger was loaded before practicing hovering and a low-rpm recovery. On approach to land during the accident flight, about 100 feet above ground level (agl), the pilot noticed the rotor rpms drop below the normal operating range. The pilot increased throttle but was unable to recover rotor rpms within the normal range. The flight instructor stated that the helicopter lost a lot of altitude quickly and there was no time to recover. The pilot attempted a forced landing on the side of a roadway but caught the right skid on uneven ground, which led to a dynamic rollover and substantially damaged the tail section and tail rotor.

The flight instructor stated that the engine had no mechanical anomalies before the flight and that the engine had “performed well” during both the accident flight and previous flights.

The helicopter likely lost power and altitude due to the pilot’s mismanagement of rotor rpm resulting in the pilot having to attempt a forced landing on uneven terrain and a subsequent dynamic rollover.

Text from the NTSB. Open the NTSB docket for CEN18LA306 for the full record.