What happened
On 8 September 2004, a Piper PA-28-161 Warrior II, registration G-BNXE, was conducting a training flight for the purpose of re-validating an IMC rating. Following a pre-flight inspection and successful engine run-up checks, the aircraft began taxiing for departure from Runway 05. This required a backtrack of approximately 8 km along the runway.
During the 180-degree turn to line up on the runway centre line, the engine suddenly ceased operation. The pilot attempted to restart the engine twice using the hot engine start procedure, but both attempts failed. While the crew was unaware of any external fire, air traffic controllers notified them that flames were visible around the engine area. The commander ordered an immediate evacuation, and both occupants exited the aircraft via the cockpit door. The airfield fire service arrived and extinguished the fire.
The investigation
Post-accident inspections of the aircraft were conducted at a local maintenance facility. Investigators found that the fire was primarily concentrated around the carburettor heat box, with heat damage extending to the lower engine cowlings and various components mounted on the rear of the engine.
Examination of the fuel system revealed no evidence of leaks, loose connections, or split supply lines. Tests performed with the fuel pumps active demonstrated that fuel was flowing correctly without leakage. The engine remained capable of turning, and the spark plugs showed that the fuel/air mixture had been correctly set. The investigation could not determine the specific reason for the initial engine stoppage.
Findings
- The fire was centered on the carburettor heat box area.
- Excess fuel likely pooled in the carburettor heat box during the unsuccessful restart attempts.
- Because the engine had stopped, the lack of airflow prevented the accelerator pump's fuel injection from being moved through the venturi, causing fuel to drip downward.
- The hot exhaust system likely acted as the ignition source for the accumulated fuel vapours.