Brantly B 2B N2284U accident near Midland, Michigan

Probable cause

The pilot's failure to maintain control of the helicopter, which resulted in a loss of tail rotor effectiveness, and his failure to promptly initiate the proper recovery technique, which resulted in a descent that could not be arrested before impacting the terrain.

NTSB analysis

The private pilot was conducting a local flight in the helicopter with a passenger. After departing from an open field, the pilot flew along the perimeter of the field, and the passenger recalled that about halfway around the perimeter of the field, the helicopter began descending, slowly at first and then more rapidly. According to the passenger, the rotor speed increased, but the helicopter continued to descend.

Ground-based video footage revealed that before it began descending, the helicopter was moving forward slowly when it yawed about 270° to the right. As it neared the ground, the helicopter again yawed to the right, completing nearly a 360° turn either immediately before or just after it contacted the ground. The helicopter came to rest on its left side. The engine continued to run after the helicopter came to rest, and the passenger shut it off.

Airframe and engine examinations did not reveal evidence of any anomalies consistent with a pre-impact failure or malfunction. Surface wind conditions recorded at nearby airports were light and variable.

Federal Aviation Administration publications regarding a loss of tail rotor effectiveness (LTE) state that in the event of a sudden, unanticipated right yaw, a pilot should apply full left pedal, simultaneously move the cyclic control forward to increase airspeed, and if altitude permits, reduce engine power. Factors that contribute to LTE are a high-power setting, which induces considerable main rotor downwash and more turbulence relative to a low power setting, and a slow forward speed, which may create variations in airflow around the tail rotor. The video footage showing a right yaw followed by a descent suggests that the pilot encountered LTE, which resulted in the 270° right yaw before the pilot was able to regain control. The additional power required by the tail rotor during the recovery reduced the power available to the main rotor and resulted in a descent that could not be arrested with the engine power available. It appeared that the pilot did not attempt to increase airspeed during the recovery, which reduced his ability to avoid impacting the ground.

Text from the NTSB. Open the NTSB docket for CEN18FA001 for the full record.