Event Description
A helicopter engaged in aerial spraying of a cranberry bog completed four passes before executing a right turn to the north to begin the next run. After completing the turn, the helicopter began to spin to the right. It completed approximately three to four rotations before stopping in a level hover. The helicopter then resumed spinning to the right, again making about three to four turns before stopping. A final spin to the right ensued, during which the helicopter collided with the bog.
The pilot stated that the uncontrolled event began after completing a right-hand application turn. The pilot did not report any lateral cyclic displacement during the last application run.
Weather Conditions
A local automated weather report indicated winds from 210 degrees at 6 knots.
Manufacturer Safety Notice
Bell Helicopter Textron (BHT) published an Operations Safety Notice in 1983 addressing unanticipated right yaw of the Bell 206 series. The notice stated that unanticipated right yaw could occur when maneuvering between hover and 30 MPH. It noted that a tail wind could reduce relative wind speed if a downwind translation occurred. Additionally, a loss of translational lift could result in high power demand and additional anti-torque requirements, including high power demand situations such as low-speed downwind turns.