What happened
On April 10, 2017, a Piper PA-28-181, registration HB-PFA, was parked at Bressaucourt Aerodrome (LSZQ) for refueling. During the engine start sequence, the pilot attempted to ignite the engine while the mixture was set to rich, the booster pumps were active, and the manual primer had been used three times. During the starting process, the pilot moved the throttle forward and backward for approximately 20 seconds, which caused additional fuel to be injected into the carburetor via the acceleration pump.
After an initial failed attempt, the aircraft was moved further along the tarmac to allow another pilot to access the fuel pump. To prevent battery drain, the pilot connected the aircraft to an external power source. Upon a subsequent attempt to start the engine using procedures intended for a flooded engine, white smoke began emerging from the engine compartment. Although the pilot initially believed the smoke was minor and proceeded to turn off electrical components and the fuel selector, the situation escalated. By the time the pilot returned with a mechanic, thick smoke and visible flames were present. The fire was eventually extinguished using portable fire extinguishers.
The investigation
The investigation focused on the sequence of engine start attempts and the accumulation of fuel within the engine system. Investigators examined the pilot's actions regarding the throttle movement and the use of the manual primer, as well as the state of the aircraft's fuel delivery components.
Findings
- The aircraft sustained heavy damage to the engine and cowlings.
- There were no fatalities and one person sustained minor injuries.
- The primary cause of the fire was an excessive accumulation of flammable fuel within the carburetor, likely resulting from the repeated priming and throttle manipulations during the failed start attempts.