What happened
On 6 June 1998, an Avid Flyer, registration G-BUBB, was conducting a private local flight from Cambridge Airport. Approximately 15 minutes after departure, the pilot and passenger detected a potent smell of fuel within the cockpit. In response, the pilot initiated an immediate return to the airfield, unlatching the passenger door to improve ventilation and avoiding the use of any electrical switches.
Upon arriving over the airfield, the pilot closed the fuel cock and executed a glide approach to the grass runway. The landing itself was completed without incident. However, as the aircraft taxied onto the southern taxiway to clear the runway, a flash was observed in the passenger footwell. A flame then spread along the doped fabric on the right side of the fuselage. The aircraft was quickly consumed by fire and was destroyed by the time the airfield fire service reached the scene.
The investigation
The investigation focused on the source of the fuel leak and the subsequent ignition. The pilot suggested that fuel had leaked from the supply lines connecting the wing tanks to the fuel cock, resulting in an accumulation of fuel on the cockpit floor. It was believed that once the aircraft's forward motion stopped, fuel dripped onto the hot exhaust pipe located beneath the passenger footwell. The ignition was attributed to hot carbon deposits on the two-stroke engine's exhaust.
The pilot also noted a period of transient resistance in the rudder pedal movement during taxiing prior to the incident. This led to the possibility that a rudder pedal might have interfered with a fuel line, potentially causing a connection to unclip from the tubular steel fuselage frame. Due to the extensive fire damage, the exact origin of the leak could not be definitively identified.
Findings
- A fuel leak occurred in the lines between the wing tanks and the fuel cock.
- Fuel accumulated on the cockpit floor and dripped onto the hot exhaust.
- The fire was ignited by hot carbon deposits on the exhaust system.
- The aircraft was destroyed by fire.