Acknowledgements: George Scheer (

 (Ed.Note: As an add-on to the previous article, should you experience, in spite of your best efforts not to, a fire during start …… )

“We have mentioned that improper starting technique can cause a fire in the engine compartment. We are all familiar with the standard advice to continue cranking in the event of a fire, but the problem is that this fire may not be immediately apparent.  

 The loud pop or bang that you will occasionally hear is usually a combustion event in the exhaust system, again caused by excessive priming, and may cause some internal damage to the exhaust system but will seldom if ever cause a fire.  Similarly, burning fuel in the intake tubes of a Lycoming engine will seldom cause significant damage.  

 The fires that damage our airplanes are almost always caused by the ignition of a pool of fuel sitting in the carb heat box - fuel that found its way there due to excessive priming or priming attempted with the throttle and accelerator pump in the carburettor.  This is fuel that never made it into a cylinder and drained back down through the intake system to puddle in the carb heat box of a carburetted airplane.

 The problem is that the ignition of a fire in the carb heat box caused by a backfire igniting that pool of fuel often produces a subtle, low-frequency “whoompf” noise that can go unnoticed.   

 The event is often recognised foremost by a sudden engine stoppage, either while the pilot is still cranking the starter or has just released the starter and the engine is beginning to spin up.  This is precisely the moment when we need to restart the engine and crank it for ten or more seconds.  If it starts, let it run for thirty seconds or so, shut down, and inspect for damage.  

 To summarize what we know:

  • Preheat when necessary.

  • Follow the checklist procedure, particularly for fuel-injected engines.

  • Prime less at first rather than more

  • Do not prime with the throttle (accelerator pump.)

  • Prime when you are ready – really ready— to start.  Not before.

  • Opening the throttle further seldom helps.

  • If the engine doesn’t start in a few seconds – stop cranking.

  • Repeat as necessary

  • f the starter begins to slow down, you are melting it down.  Stop.  Go have a cup of coffee. Do not come to the maintenance department and say, “The starter overheated.”  You overheated the starter.   Draining a battery or frying a starter is not something that happened to you – it is a choice you made.

  • Get help if you need it.

  • If you have any reason to believe that a fire has started in the intake manifold continue cranking. Restart the engine and let it run for 30 seconds.

 To prevent and manage an engine fire:

  • Follow the good practices outlined above.

  • Realise that a fire in the intake or carb heat box may not be immediately apparent.

  • If you suspect a fire, continue cranking to draw the fire into the engine. Keep the engine running for a few minutes, shut down, and inspect for damage.

  • If the fire becomes uncontained, shut down the airplane, shut off the fuel, exit the airplane, and (only) if safe and practical, use a designated fire extinguisher to extinguish the fire.


Tony Birth