What happened
On 15 July 2021, an Agusta A109C, registration G-HBEK, was conducting a private flight from a site in Dorset toward Dunkeswell Aerodrome. Following a landing gear malfunction during the initial departure, the pilot elected to return to the original departure point.
As the helicopter approached the private landing site in Organford, it began a right-hand turn to head south. During this maneuver, the aircraft experienced an unexpected nose swing to the right. The pilot attempted to counteract this by applying full left pedal and left cyclic inputs, but the aircraft began drifting sideways to the left while maintaining a southerly heading.
As the pilot increased the collective to manage the descent, the rightward rotation became uncontrollable. Fearing a loss of tail rotor drive, the pilot chose not to attempt a climb and instead cut the engine power in an attempt to straighten the aircraft. The helicopter subsequently struck the ground, resulting in one minor injury to the pilot and the aircraft being damaged beyond economic repair.
The investigation
The AAIB examined the aircraft and consulted with the manufacturer. The investigation found no mechanical defects in the tail rotor control system, and the tail rotor gearbox was found to be in good condition with sufficient oil. While the tail rotor driveshaft had separated from the main rotor gearbox, investigators determined this was likely a result of the ground impact rather than a pre-existing failure.
Meteorological data from Bournemouth Airport indicated that winds were shifting during the flight. The investigation considered how the aircraft's speed, power settings, and the relative wind direction during the turn might have contributed to the loss of directional control.
Findings
- The aircraft was operating in a phase of flight where it was susceptible to loss of tail rotor effectiveness (LTE) or overpitching.
- The combination of a high power setting, decelerating flight, and a turn downwind may have caused the pilot to reach the limits of tail rotor authority.
- There was no evidence of a mechanical failure in the tail rotor or driveshaft prior to the impact.