What happened
On May 24, 2003, at approximately 08:30, a Cessna 172-M, registration EC-DZF, was prepared for a local flight at Seville Airport. Following a standard pre-flight inspection, the pilot attempted to start the engine. The pilot engaged the primer three times before attempting the first start, which was unsuccessful. After a brief pause, a second start attempt was made, at which point a flame erupted from the induction system.
The pilot immediately shut off the electrical power and fuel supply. Although the pilot managed to extinguish the initial flame using the onboard fire extinguisher, the fire reignited in the same area. The pilot subsequently obtained a second extinguisher from a nearby hangar to fully suppress the fire. Airport fire services responded to the scene but did not need to intervene directly. There were no injuries reported.
The investigation
The investigation focused on the sequence of the engine start procedure and the pilot's emergency response. The examination of the aircraft revealed significant damage to the engine cowling, propeller, and induction system. The investigation reviewed the aircraft's flight manual, specifically regarding engine priming and emergency fire procedures. It was noted that while three primer strokes are standard, the subsequent attempt to restart after the initial failure led to an accumulation of excess fuel.
Findings
- The fire was caused by overpriming, where an excess of fuel accumulated in the cylinders and induction system.
- The pilot's decision to cut the electrical power immediately upon seeing flames prevented the engine from sucking the flames and accumulated fuel through the carburetor and into the engine.
- The flight manual specifically instructs pilots to continue cranking the engine during an induction fire to prevent flames from advancing through the system.
- The cessation of fuel flow and the lack of throttle adjustment contributed to leaving unburned fuel in the induction lines, which later reignited.