What happened
On 27 January 2014, a Hughes 369D helicopter, registration G-CCUO, was performing a private flight near Droitwich, Worcestershire. The aircraft was being repositioned to its home base following an annual maintenance inspection.
During the flight, the pilot attempted to climb vertically into a high hover. While in this position, the pilot found that the yaw pedals provided no directional control, and the aircraft began to spin. As the rotation accelerated, the pilot became disoriented and lowered the collective to force a landing. The helicopter drifted to the right and struck trees in a wooded area adjacent to the apron. The impact left the aircraft on its side, partially submerged in a pond. The pilot sustained minor injuries but was able to escape the wreckage through a broken windscreen.
The investigation
The AAIB examined the aircraft's mechanical condition and the flight environment. Investigators found that the only recent work performed on the yaw control system involved a routine oil change for the tail rotor gearbox. A post-accident inspection confirmed that the connection between the yaw pedals and the tail rotor blades was intact and free of defects.
Environmental conditions at the time included a 15-knot wind from 250°. The investigation focused on whether aerodynamic factors, rather than mechanical failure, contributed to the loss of control.
Findings
- The aircraft was operating in a high power setting during a vertical climb into a high hover.
- The 15-knot wind was sufficient to induce translational lift, which can alter the airflow through the tail rotor.
- The loss of tail rotor effectiveness (LTE) was the most likely cause of the accident.
- The specific wind conditions likely caused main rotor blade tip vortices to disturb the airflow to the tail rotor, leading to the uncommanded spin.