What happened
On a mission south-west of Grande Prairie, Alberta, a Bell 206B was tasked with retrieving a worker suffering from anaphylactic shock. While searching for the target location, the pilot spotted a yellow bus on a road and decided to descend to approximately 40 feet above ground level to verify the vehicle's identity. The pilot performed three low-speed circuits around the bus at speeds between 5 and 10 miles per hour.
After completing the third circuit, the pilot attempted to climb away by applying engine power and collective inputs. During this maneuver, the helicopter suddenly experienced a rightward yaw. Despite the pilot applying full left pedal to counteract the rotation, the aircraft entered a spin. To mitigate the impact, the pilot reduced engine power and lowered the collective to perform an autorotation. The helicopter landed upright, though the landing caused damage to the main and tail rotor blades, the power train, the vertical fin, and the right skid. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's flight controls, tail rotor drive system, and maintenance records. No mechanical discrepancies, interference in the flight control system, or failures in the tail rotor authority were identified. The investigation also reviewed the pilot's qualifications, noting approximately 1,800 total flight hours, including 715 hours in the Bell 206B and significant experience as a flight instructor.
Technical documentation from Bell Helicopter Textron Inc. and the FAA regarding low-speed flight characteristics was reviewed. This included information on how certain flight conditions in single-rotor helicopters can lead to a loss of tail rotor effectiveness (LTE).