What happened
On 9 September 2012, a Piper PA-28-151 Cherokee Warrior, registration G-BOTF, was at Southend Airport for a private flight. Following a period of recent operation, the pilot taxied the aircraft to the fuel pumps to refuel the aircraft with two passengers on board.
During the start sequence, the pilot attempted to start the engine, which was still warm from a previous flight. The engine failed to ignite, and the pilot proceeded to crank the engine using the starter motor while repeatedly advancing and retarding the throttle. During this process, smoke was observed emerging from the engine compartment, which was quickly followed by flames. The pilot immediately switched the fuel cock to the OFF position and oversaw the evacuation of the passengers. The airfield fire service responded to the scene and successfully extinguished the fire.
The investigation
The investigation focused on the engine bay and the fuel system. Examination of the aircraft revealed extensive fire damage to the inside of the engine bay and the lower forward section of the engine cowling. The origin of the fire was identified near the bottom of the engine, in close proximity to the carburettor.
Engineers inspected the fuel system within the engine bay and found no evidence of loose fittings, split hoses, or any other pre-existing mechanical defects. The investigation also noted that the pilot had experienced similar starting difficulties on the same aircraft the previous week. A review of historical AAIB records for the Piper PA-28 series showed seven similar engine fires between 2000 and 2012, with three previously identified as being caused by over-priming a hot engine.
Findings
- The fire originated near the carburettor area.
- There were no mechanical defects or leaks found in the engine bay fuel system.
- Over-priming the hot engine was the likely cause of the fire.
- It is believed that fuel was pumped into the carburettor venturi by the accelerator pump and, because the engine was hot, the fuel pooled and vaporized, creating an ignitable atmosphere.