Overpriming—typically done during an attempt to start a cold engine—is a leading cause of engine fires.
In a Cessna 172N, excess fuel may ignite in the intake manifold. The pilot’s operating handbook will have an emergency checklist for this event, but you should commit it to memory. A fire is no time to be digging through a POH.
- Fire Starter
After too many pops of the primer, excess
fuel collects in the intake manifold. When
you turn the ignition and supply the spark,
that excess fuel can ignite.
- Danger signs
You may smell smoke or burning oil, or see smoke come out of the cockpit air vent. Another clue is if someone outside the airplane starts gesturing wildly at you.
- If the engine starts
Run it for a minute to suck flames back through the carburetor and extinguish the blaze. Where’s your fire extinguisher, by the way? Then shut down the engine (see below) and get out of the airplane (see 5).
- If the engine doesn't start
Keep throttle full open, put mixture to idle cutoff.....(4a) continue cranking......(4b) then turn off the fuel selector, ignition, and master.
- Extinguish the flames
Get out of the airplane immediately. Use the fire extinguisher to extinguish any blaze, if necessary. The airplane will need to be inspected before it can fly again.