What happened
On 8 July 2007, a Thruster T3/00 microlight, registration G-MYAR, was performing a private flight from a 480-metre grass farm strip at Horse Leys Farm, east of Loughborough. The aircraft had completed two short flights earlier that morning and was departing again with a half-full 40-litre fuel tank.
While the takeoff initially appeared normal, the pilot noted a later liftoff compared to previous sorties, which was attributed to the fuel weight and soft ground conditions. At an altitude of approximately 30 feet, the engine power began to diminish. As the pilot focused on the power loss, the aircraft drifted left of the runway centerline. Unable to maintain sufficient height or speed to return to the strip, the pilot executed a forced landing straight ahead into a mature wheat crop. During the landing, the aircraft struck a hedge and inverted. The pilot, who sustained one minor injury (a strained neck), fell from the seat upon releasing the harness.
The investigation
The investigation examined the engine performance and the fuel system following the power loss. The pilot noted that during the flight, the carburettors had experienced over-pressurisation, causing fuel to drip onto the windscreen. To mitigate this, the pilot had deactivated the electric fuel pump and relied solely on the mechanical pump. While the pilot initially suspected a blocked vent in the fuel tank cap, physical examination of the vent hole revealed no blockage.
Findings
- The engine power loss was likely caused by a partial vacuum forming in the fuel tank due to a blocked vent in the tank cap.
- The pilot suggested that the pressure of the fuel against the vent hole during the aircraft's inversion may have cleared the obstruction, preventing further confirmation of the blockage.
- A contributing factor was the pilot's distraction by the fading engine power, which allowed the aircraft to drift off the runway centerline.