NTSB Aviation Investigation Preliminary Report - N715KV
According to the pilot, upon reaching Kalalau beach, he accomplished a left turn away from the shoreline as part of the normal flight profile. Upon entering the turn, the pilot experienced a high frequency vibration throughout the helicopter that came in waves and became stronger each time. Subsequently, the helicopter started an un-commanded right yaw that could not be corrected with input from the left anti-torque pedal. The helicopter quickly began to rotate clockwise, completing about 2 rotations, and the pilot entered the helicopter into an autorotation. He rolled the throttle to idle and attempted to increase the airspeed for better directional control.