What happened
On 2 December 2000, a Robinson R2-Beta, registration G-BNUZ, was conducting a private local flight from Sherburn-in-Elmet airfield. The flight, carrying a pilot and one passenger, proceeded toward a training area south of the airfield. After several maneuvers, the pilot requested permission to enter the controlled airspace near Church Fenton to return to the airfield.
While flying on a southwesterly track toward the airfield at approximately 1526 hrs, the helicopter experienced a sudden and catastrophic event. Witnesses in the village of Biggin reported hearing a metallic bang and the sound of the engine faltering. Following this, debris was seen falling from the aircraft, and the tail boom appeared to crease as the rotor blades began to rotate at a significantly reduced speed. The helicopter descended steeply and struck the ground near a hedgerow. The impact resulted in two fatalities.
The investigation
Investigators examined the wreckage and found that the aircraft had suffered significant structural damage during flight and upon impact. The tail boom had been struck by the main rotor, and the tail rotor gearbox had been detached. Analysis of the cockpit revealed that the carburettor heat control knob was in the 'Cold' position, though the actual heat slider in the air filter box was found in the 'full-hot' position.
Crucially, the 'Low Rotor RPM' warning light showed evidence of being illuminated just before impact. The engine and mechanical components, including the main rotor gearbox and freewheel clutch, were found to be in good working order prior to the accident. There were no mechanical defects identified that would have caused a sudden engine failure or loss of control.
Findings
- The primary cause of the accident was likely carburettor icing, which developed as the aircraft descended through moist, cool air.
- The electronic RPM governor in the Robinson R22 Beta likely masked the initial symptoms of icing by automatically adjusting the throttle to maintain engine speed, preventing the pilot from noticing the engine's power loss.
- The pilot was not briefed on earlier reports from the day regarding engine performance issues, as the pre-flight paperwork had not been completed.
- Environmental factors, including low sun glare and the high workload of joining the landing circuit, may have prevented the pilot from detecting the onset of icing until it was too late to react.