What happened
On 6 February 1998, a Robinson R22 Beta, registration G-DRAI, was conducting a private flight from a landing site near Biggleswade to Wycombe Air Park. Following maintenance, the pilot had refuelled the aircraft and planned a 40-minute flight. During the approach to the airfield, the helicopter entered the 'November' training area and was directed by Air Traffic Control to a holding point.
While performing a hover taxi at an altitude of approximately 6 feet, the aircraft encountered a sudden, powerful gust of wind. This wind caused the helicopter to sink unexpectedly. Although the pilot attempted to increase power to recover, the aircraft experienced a momentary loss of engine power and bounced upon hitting the ground. During this contact, one of the main rotor blades struck the tailboom, likely exacerbated by 'blotting' or bladesailing effects caused by the gusty conditions.
The investigation
Investigators examined the aircraft's fuel systems after the pilot reported that the 'low fuel' warning light had illuminated once the aircraft was stationary, despite the pilot's belief that fuel levels were sufficient for the flight. Upon draining the tanks, only about 0.5 US gallons of fuel remained.
Testing revealed that the fuel gauges were providing inaccurate readings. Specifically, when the tanks were completely empty, the gauges still indicated 5 US gallons in the main tank and 1.5 US gallons in the auxiliary tank. The investigation determined that the main fuel tank contents indicator was sticking.
Findings
- The primary cause of the rotor blade strike was a sudden, strong gust of wind that caused the aircraft to sink during a low-altitude hover taxi.
- The aircraft's fuel gauges were malfunctioning due to a sticking transmitter, which provided an inaccurate representation of the actual fuel remaining.
- There were no injuries to the two persons on board, and the aircraft sustained damage to the main rotor blade and tailboom.