What happened
On 7 July 1999, a Robinson R22 Beta, registration G-WFOX, was involved in an accident at Tatenhill Airfield, Leicestershire, during a training flight. Following a thirty-minute break after a successful flight, a student pilot began preparations for a dual training sortie. The incident occurred as the pilot was switching on the governor.
Upon engaging the governor, the engine accelerated unexpectedly, accompanied by a high-pitched noise and intense, high-frequency vibrations. The helicopter simultaneously experienced a sudden rightward turn that the pilot could not counteract using the left pedal. As the aircraft bucked violently, the tail rotor struck the ground. Before the pilot could execute an engine shutdown, the helicopter came to rest in a nose-up position on the rear skids. During this sequence, the aircraft rotated approximately 120 degrees. A main rotor blade struck the ground, which resulted in the main rotor mast shearing, causing the rotor head and blades to detach from the fuselage.
The investigation
The investigation focused on the cause of the sudden engine acceleration and the subsequent mechanical failure. The pilot, who had recently verified the magnetos at 100% rotor RPM, initially suspected a mechanical failure within the governor system.
Technical examinations were conducted on the governor motor assembly, the governor control box, and the tach magneto. These components were returned to the manufacturer for detailed inspection. The investigation established that there were no pre-accident failures in the aircraft systems or controls, and all inspected components were found to meet factory specifications for new parts.
Findings
- The engine accelerated unexpectedly during the transition to governor control.
- The rapid onset of vibrations and the sudden rotation of the aircraft made it difficult for the student pilot to maintain control.
- The main rotor mast sheared due to a main rotor blade striking the ground.
- While the exact cause of the upward movement of the collective pitch lever remained unidentified, some upward movement was necessary for the aircraft to become airborne.