I always thought this is the result of a cracked (or more than cracked) exhaust system, but actually somebody got it in a TB20 in the US, and the flames came out of the air filter in the front.
it was the 13-th hot start of the day, been roaming the “Big Sky” country, visiting airport after airport and right at Huntington Muni 69V, Utah, I kind of hastily advanced the mixture forward before the engine had fired… the prop turned a few more times and when I saw that it will not fire I stopped the starter. At that very second, I could not believe my eyes as there were flames coming from in front of the cowling
It burned right through the air filter, melting it
I have seen it happen when the pilot was having trouble starting and then started pumping the throttle whilst the engine was cranking.
So as a remainder to everybody – if it happens to you during engine start that somebody is shouting that there is a fire from engine air inlet – mixture close, full throttle and KEEP CRANKING the engine. If it starts then the fire will go out immediately. If it doesn’t – keep the starter for 30sec at least. The burning fuel will be sucked inside cylinders.
I have seen it happen when the pilot was having trouble starting and then started pumping the throttle whilst the engine was cranking.
Especially on carbureted engines in winter.
Raven wrote:
if it happens to you during engine start that somebody is shouting that there is a fire from engine air inlet – mixture close, full throttle and KEEP CRANKING the engine. If it starts then the fire will go out immediately. If it doesn’t – keep the starter for 30sec at least. The burning fuel will be sucked inside cylinders.
This.
It has happened to me twice, and both times, continued cranking prevented a much worse event. Keep cranking until the battery no longer has energy to turn the engine over, then get out with fire extinguisher in hand. Know that you may have to have the starter overhauled, but it’ll be less costly than the fire would have been. Examine the engine compartment afterword for remaining fire, the foam covering on my oil breather was still on fire, requiring the fire extinguisher in the oil filler door, but very little damage.
The O-360 installation in the TB10 has no primer. You must pump the throttle to prime, indeed it’s in the POH.
Same for the RV-8 I’ve been flying recently.
I was reading an article in one of the, French aviation magazines recently. It was more about fuel, additives and octanes really but it might not be off topic here.
It described how Avgas lead can cause “castellation” / castle shaped crusts of lead on the head of the piston. Under certain conditions these start to burn and smoulder, then when you prime the engine the cylinder bursts into flames which then spreads. The comments with mix full lean (étouffoir) and cranking the engine to and burn the fuel in the cylinder, is advice I have read in several POHs.
The word backfire came about for a reason…. It actually means a fire moving backwards though the intake tract, as opposed to its common use for a pop through the exhaust.
The problem with relying on the accelerator pump to prime the engine versus a dedicated primer is that the fuel injected at the bottom of the intake tract instead of adjacent to the cylinders. In the event of a backfire it takes longer for that burning fuel to be sucked into the cylinders.
In my view there’s a common cause to most startup fires: – poor starting.
When a Warrior I was involved in went through a phase of poor starting, the engineer of the time drew on an elaborate retinue of excuses to avoid having to find out what was actually wrong with it. A renter took it to a strip in Wales and got a fire on startup. A nearby pilot grabbed his own extinguisher, rushed over and put the fire out. That’s how I know how much aviation extinguisers cost.
Very unwisely, it was patched up and flown back to base. (Wings off would have been altogether more sensible). There a fellow group member who happened to be a race car mechanic experimented and showed that only three pumps of the throttle were needed to get liquid fuel running onto the bottom of the cowling. The CFI had been advocating throttle pumping as a means of overcoming the poor starting. This was made even worse by cracks in the hot air changeover box, but this isn’t sealed against fuel leaks anyway.
A conversation with the ‘engineer’ ensued and eventually it became the best starting Warrior I’ve ever known. No more fires.
