What happened
On 25 June 2015, a Robinson R44 II Raven II, registration G-CDXX, was parked on a concrete extension near a hangar at Leicester Airport. The pilot was preparing for a private local flight and had finished the necessary pre-flight inspections. As the pilot began to gradually increase the rotor RPM to approximately 80%, the aircraft experienced a sudden and rapid yaw to the left. This movement continued until the helicopter had rotated roughly 290 degrees, at which point it tipped over onto its right side. During the impact with the ground, the forward right door opened. The pilot was able to exit the aircraft without assistance and sustained minor injuries.
The investigation
The investigation was supported by footage from two CCTV cameras that captured the sequence of events. The examination of the aircraft revealed damage to the main rotor blades, a bent tail cone, and a snapped right skid. The investigation focused on the mechanics of the sudden rotation during the engine start sequence.
Findings
- The aircraft was undergoing rotor RPM increase at the time of the incident.
- Excessive left pedal application at the moment of governor engagement can cause a rapid leftward yaw due to the high effectiveness of the tail rotor.