Incident Overview
On February 21, 2002, a Piper PA-28-161 (registration EC-GFH) was preparing for its first flight of the day at the Cuatro Vientos Airport in Madrid, Spain. The aircraft, used for pilot training, was parked on the apron with a student pilot and an instructor on board. While the student attempted to start the engine, the instructor noticed smoke in the cockpit and instructed the student to open the storm window. A burning smell entered the cockpit.
Evacuation and Fire Response
The instructor immediately ordered the student to evacuate the aircraft, then performed the "engine fire during start" procedure from the aircraft manual before also exiting. From outside, they observed large flames exiting the exhaust. The fire was extinguished using a fire extinguisher from a fuel tanker truck that was nearby; the instructor chose this extinguisher over the aircraft's onboard extinguisher, deeming the latter insufficient due to its small capacity.
The fire was not visible from the control tower or the fire station. The fire department was alerted by another aircraft taxiing nearby, as the crew had no means of communication with the tower or firefighters after evacuating. However, their intervention was unnecessary as the fire was controlled before their arrival.
Damage and Injuries
The aircraft sustained minor damage to the engine and its cowling. Both occupants were uninjured.
Investigation Findings
During the investigation, the instructor stated that the student had followed the "cold engine start" procedure from the aircraft manual. After several unsuccessful attempts, the instructor assumed the engine might be flooded and instructed the student to perform the "flooded engine start" procedure. It was during this procedure that smoke was noticed.
Post-incident inspection revealed that the air filter was damaged by fire. There were no signs of fire caused by fuel leaks, electrical issues, or other sources. Fuel leaks were observed in the engine compartment but were not involved in the incident.
The aircraft manual's cold engine start procedure recommends cranking for no more than 10 seconds, then priming and repeating if the engine does not start. It does not explicitly state how many attempts should be made before switching to the flooded engine start procedure.
Probable Cause
The investigation concluded that the most probable cause of the incident was a carburetor explosion occurring during one of the start attempts, resulting from an accumulation of fuel, partly in vapor form, in the engine intake.