What happened
On 21 May 2009, a Brantly B2B, registration G-BPIJ, was engaged in an aerial work flight for the purpose of revalidating a pilot's type rating. While operating at Hardwick Airfield, the pilot under instruction was maintaining a low hover at approximately 6 feet. During a commanded right turn to point the aircraft downwind, the helicopter began to yaw to the right at an accelerating rate while simultaneously climbing.
As the aircraft climbed to a height between 20 and 30 feet, the yaw rate increased rapidly. The instructor, who was on board, applied full left pedal and lowered the collective to recover rotor speed. Despite these efforts, the aircraft continued to rotate through several turns before descending. Upon touchdown, the aircraft continued to yaw, causing the left skid to collapse and the helicopter to roll onto its left side. The main rotor blades struck the ground, resulting in the aircraft being beyond repair. No injuries were sustained by the two crew members.
The investigation
The investigation examined the aircraft's mechanical condition and the flight dynamics during the loss of control. The instructor provided testimony regarding the suddenness of the yaw and the difficulty of intervention. Investigators inspected the wreckage for any evidence of a malfunction in the tail rotor drive mechanism or the pitch control linkages. No disconnections or mechanical failures in the tail rotor system were identified.
Findings
- The primary cause of the incident was the loss of tail rotor effectiveness during the hover.
- High main rotor torque, combined with an increase in collective pitch and a reduction in rotor speed, likely led to marginal tail rotor authority.
- The instructor's ability to intervene was limited because the aircraft was already in an uncontrolled state before control could be effectively applied.
- The aircraft's descent and subsequent roll were driven by the continued yawing motion after touchdown.