Primary finding
Probable cause
The pilot’s improper decision to approach the airport and enter a low altitude hover with a gusting quartering tailwind, which resulted in a loss of tail rotor effectiveness during a turn at a low altitude.
Investigator assessment
Analysis narrative
After a west-southwest approach to the airport the pilot entered a low altitude hover near a taxiway intersection where he intended to turn left and join a north/south taxiway before continuing in a hover taxi south toward the ramp. During the counterclockwise turn to join the taxiway, the helicopter’s yaw rate increased as the tail passed through the north-northeast wind. The pilot allowed the helicopter to continue in the turn, despite an increasing left yaw rate, until the nose of the helicopter had realigned with the wind. However, at that point, he was unable to stop the counterclockwise rotation and the helicopter completed at least 2 revolutions before a landing skid struck the ground and the helicopter spun off the taxiway into a grass easement. The pilot and two medical personnel were not injured. The horizontal stabilizer attach fitting on the tail boom was fractured and required replacement. The operator did not report any mechanical malfunctions with the helicopter that would have precluded normal operation. According to a weather report issued about 6 minutes before the accident, the surface wind at the airport was from north-northeast at 8 knots. During the subsequent hour, the wind direction remained unchanged, but the wind speed had increased to 11 knots with 17 knot gusts. A loss of tail rotor effectiveness likely occurred when the helicopter encountered a wind gust during the left turn, which resulted in an increasing counterclockwise yaw rate that the pilot was unable to control.