What happened
On 9 May 2006, a Hughes 500C-369HS helicopter, registration G-ORRR, was conducting a private flight from Checkendon to Wycombe Air Park. During the climb out, the pilot reported experiencing erratic fluctuations in engine power. As the aircraft approached the airfield, the pilot attempted to manage the instability by reducing engine torque and airspeed.
While attempting to navigate around trees to reach a chosen landing site, the pilot perceived the engine power had dropped to nothing. In response, the pilot entered an autorotation and attempted to select a landing area. During this maneuver, the engine power briefly returned, leading the pilot to attempt to recover the situation by raising the collective. However, the engine failed to respond, and the aircraft' and airspeed decreased rapidly. The helicopter struck the ground heavily at approximately 40 to 50 feet above a hill, causing the aircraft to roll onto its side. The helicopter was destroyed, though the pilot escaped without injury.
The investigation
Investigators examined the wreckage and the engine components. While the pilot reported a total loss of power, the damage to the main rotor head indicated that the rotor was still rotating under engine power at the time of the impact. The engine was removed for extensive ground testing by Rolls-Royce. Tests of the fuel control unit, governor, and high-pressure fuel pump showed all components were within acceptable limits. No evidence of air leaks in the fuel system was found, and the fuel itself was of a satisfactory standard.
During the examination of the fuel system, it was discovered that the low-pressure fuel cock operating cable had become disconnected from its arm. However, this was found to have occurred after the accident during the recovery of the aircraft. The investigation also noted that the engine was fitted with a governor typically used for twin-engine installations, but testing confirmed this would not have contributed to the accident.
Findings
- The investigation could not identify a specific cause for the reported power fluctuations.
- The engine did not actually stop during the flight, despite the pilot's perception of total power loss.
- The pilot's focus on maintaining control and avoiding trees during the power fluctuations prevented the activation of the start fuel pump, which might have otherwise smoothed the engine's operation.