What happened
On 24 August 2011, a Midget Mustang, registration G-IIMT, was performing a private flight from Edge Hill. Following a period of ground time at Gloucester Airport, the pilot commenced a takeoff from Runway 22. During the climb, at an altitude between 100 and 200 feet, the engine suffered a sudden and significant loss of power.
Fearing an overrun of the runway, the pilot decided not to continue straight ahead but instead banked left to utilize the intersecting Runway 18, which extends into a taxiway. The aircraft touched down heavily on the left mainwheel and tailwheel first. While the pilot was able to stop the aircraft on the taxiway and exit the cockpit without assistance, the impact caused damage to the wing and the landing gear structure. There were no injuries to the pilot.
The investigation
Investigators examined the aircraft's fuel system, which featured a modification designed to pressurize the fuel tank using ram air from a pitot tube located under the fuselage. This system was intended to compensate for the marginal fuel pressure provided by the aircraft's gravity-feed design.
Upon inspection after the accident, the pilot noted that the knurered screw on the fuel filler cap was loose, meaning the cap was no longer providing a proper seal. An inspection by a Light Aircraft Association (LAA) inspector confirmed that this loose cap would have caused a loss of the necessary ram air pressure. The investigation also considered the status of the electric fuel pump, which the pilot could not definitively recall activating for the takeoff.
Findings
- The primary cause of the engine power loss was a loss of fuel header pressure.
- The loose fuel filler cap prevented the pressurized fuel tank from maintaining the required ram air pressure.
- The reduction in pressure likely allowed for the development of a vapour lock within the fuel lines.
- The accumulation of vapour in uninsulated fuel lines in the engine compartment was a contributing factor, potentially exacerbated by the period the aircraft sat on the ground.
- The failure to activate the electric fuel pump may have also contributed to insufficient fuel pressure during the takeoff phase.