Guidance for return to service after engine fire.

[Shadrach]

Folks,

I am looking for guidance on returning an engine to service after an engine compartment fire during a failed start.  No, I did not set my F model on fire. However, being a stone's throw from the fuel farm, I have seen my fair share of engine fires during start up.  The damage has varied from none to minor paint work. That being said, I can find no guidance from Lycoming or Continental on external and internal inspection protocol.  Your thoughts and experience appreciated.

[1980Mooney]

2 hours ago, Shadrach said:

Folks,

I am looking for guidance on returning an engine to service after an engine compartment fire during a failed start.  No, I did not set my F model on fire. However, being a stone's throw from the fuel farm, I have seen my fair share of engine fires during start up.  The damage has varied from none to minor paint work. That being said, I can find no guidance from Lycoming or Continental on external and internal inspection protocol.  Your thoughts and experience appreciated.

I am trying to understand where the highest heat was located.

Was this:

• An over-priming event in which liquid fuel somehow running out of the engine intake or exhaust pooled somewhere inside the cowling (or on the ground) and ignited on start?
• An intake backfire in which liquid fuel/or rich mixture ignited inside your intake system and perhaps externally past the intake filter?
• An exhaust event in which liquid fuel ignited inside your exhaust system and perhaps out the tailpipe?

Edited February 21 by 1980Mooney

[Hank]

2 hours ago, Shadrach said:

However, being a stone's throw from the fuel farm, I have seen my fair share of engine fires during start up.  

Wow! For seven years I was in the first hangar behind & facing the fuel pump, close enough that I would pull my plane from the pump to my hangar after filling up.

I've never seen an airplane engine fire. But I did watch a Beetle burn up from a broken fan belt the one year I lived at the top of a steep hill . . . .

What I would do is pull my plane to the maintenance hangar and have them check it out! Remove cowl. Look for signs of heat and fire--scorch marks, melted stuff, and see what was affected, then check those components (and things nearby) as needed.

Just like "what to inspect if you have an accident," there is so much variation in possibilities that I don't think a comprehensive "check these items" list is possible to create.

[1980Mooney]

2 hours ago, Shadrach said:

 I have seen my fair share of engine fires during start up.  

The only engine fire that I have witnessed in 60 years was when 2 classmates tried to hand prime a V-8 w/ 4 barrel carb.   The rule was to always put the air filter back on before cranking.  Well one guy was pouring gasoline from a large paper cup into the carb throats as the other cranked the engine.  He poured too much gasoline in to start with, puddling on the closed throttle plates and in the intake runners. He was still holding the cup near the carburetor as the engine cranked, then immediately flooded as the throttle plates opened while still cranking and then a huge flame shot straight up.  The first guy, startled backwards, dropped the cup causing a second flare up.  Surprisingly he only got minor burns and engine was not visibly too burned.  But the hood of the car, which was up at about a 45 degree angle, had all the paint burned off the outside center part.

 

Edited February 21 by 1980Mooney

[Shadrach]

28 minutes ago, 1980Mooney said:

I am trying to understand where the highest heat was located.

Was this:

• An intake backfire in which liquid fuel ignited inside your intake system and perhaps externally past the intake filter?
• An exhaust event in which liquid fuel ignited inside your exhaust system and perhaps out the tailpipe?
• An over-priming event in which liquid fuel somehow running out of the engine intake or exhaust pooled somewhere inside the cowling (or on the ground) and ignited on start?

Nothing to do with my engine or a specific event.  I am looking for general guidance that would help one determine "if" heat levels were significant enough to warrant anything beyond cleaning.. Obviously damage to the ignition harness and other accessories warrants an external inspection, beyond that I have not found much.

[1980Mooney]

2 minutes ago, Shadrach said:

Nothing to do with my engine or a specific event.  I am looking for general guidance that would help one determine "if" heat levels were significant enough to warrant anything beyond cleaning.. Obviously damage to the ignition harness and other accessories warrants an external inspection, beyond that I have not found much.

Sorry I mis-read your comment.  My answer is still the same - "it depends" where the "fire" was.  George Braly on Beechtalk has commented that a true engine induction backfire on our flat aircooled engines is exceedingly rare.

• "It is unlikely to be a real backfire in the induction system.
  
  The air in the induction system is A) cold & b) 20% O2.
  
  The gas in the exhaust system is A) hot & b) ~ 2-3% O2.
  
  If you did, some way, inject a very lean F-A charge into the induction system - - you sort of have created a local microcosm of the environment of every carbureted engine operating with very very very lean mixtures. Too lean to auto ignite. NBD. Really have a hard time doing that - - since the exhaust stroke happens before the next time the intake valve opens.
  
  If you inject a very lean F-A charge into the exhaust system, then the conditions for auto-ignition do exist. And then "boom" or whatever."

If it is an exhaust backfire then it could loosen/damage couplings/slip joints/heat exchanger & shroud, etc

If it is from over-priming with liquid fuel somehow running out puddling inside the cowling, down the cowling/tail pipe/nose gear or puddling on ground before igniting, then damage may be nothing to catastrophic.

[Shadrach]

26 minutes ago, 1980Mooney said:

Sorry I mis-read your comment.  My answer is still the same - "it depends" where the "fire" was.  George Braly on Beechtalk has commented that a true engine induction backfire on our flat aircooled engines is exceedingly rare.

• "It is unlikely to be a real backfire in the induction system.
  
  The air in the induction system is A) cold & b) 20% O2.
  
  The gas in the exhaust system is A) hot & b) ~ 2-3% O2.
  
  If you did, some way, inject a very lean F-A charge into the induction system - - you sort of have created a local microcosm of the environment of every carbureted engine operating with very very very lean mixtures. Too lean to auto ignite. NBD. Really have a hard time doing that - - since the exhaust stroke happens before the next time the intake valve opens.
  
  If you inject a very lean F-A charge into the exhaust system, then the conditions for auto-ignition do exist. And then "boom" or whatever."

If it is an exhaust backfire then it could loosen/damage couplings/slip joints/heat exchanger & shroud, etc

If it is from over-priming with liquid fuel somehow running out puddling inside the cowling, down the cowling/tail pipe/nose gear or puddling on ground before igniting, then damage may be nothing to catastrophic.

Fuel puddles in the air box when an updraft carb is over primed. In cold temps fuel atomizes poorly. Gravity wins. I’ve seen aircraft with no electrical system catch fire during hand propping. In these kinds of situations, I can’t say where the fire starts only that most of the burn occurs in the air box.

[1980Mooney]

10 minutes ago, Shadrach said:

Fuel puddles in the air box when an updraft carb is over primed. In cold temps fuel atomizes poorly. Gravity wins. .... In these kinds of situations, I can’t say where the fire starts only that most of the burn occurs in the air box.

Given the scarce or non-availability of the bellows on vintage Mooney's that could be very bad.....

[EricJ]

In A&P school we were running our C340 and the #1 engine caught fire, pretty significantly.   Flames were coming out of the vents on top of the cowl, and burning fuel was flowing out the cowl flaps.   We got it shut down and it took a little while and a couple attempts to put it out, but we got it out.

Somebody in the previous class that was supposed to prep it (our class was just running it), left the fuel line fitting through the baffling to the wet fuel pressure gauge very loose, so basically it was fuel burning from there around the top of the engine, around the accessory case, etc.   We cleaned it up and there was very, very little damage to anything.   There were essentially no repairs required.   I was surprised, but it was only fuel burning and the fire didn't get big enough to get hot enough to damage anything else.   I'm sure if we hadn't shut it down promptly and put it out right away, it would have been much worse.

That's my only personal experience with such a thing, but I think in general the usual inspection criteria apply regarding integrity of parts, etc.    Fiberglass pieces will be suspect if they've discolored or no longer pass a tap test, and if something like that is questionable it'd be a good idea to look for a materials expert (e.g., the airplane builder, the supplier of the fiberglass system, etc.).

[PT20J]

Should I drift the thread by telling my engine fire story? Of course not.....but I will 

Senior year in high school and know-it-all buddy stuck the distributor back in the engine of his '57 Chevy without timing it. "Doesn't matter", he said. Of course it didn't start, so he rustled around the garage and found a can of ether that his father kept for euthanizing rats (don't ask) and dumps a slug down the air horn. Didn't replace the air cleaner, of course. Get's in and cranks up. I was just turning dusk and it was BEAUTIFUL!

[A64Pilot]

I’ve had one and seen the results of another.

‘I set my C-85 on fire from overpriming, some C-85’s inject fuel into the cylinders, mine does into the throat of the carb.

Anyway once I figured out I was on fire, full throttle and motor the starter in the idea of sucking the fire in. Line guy came and squirted it with dry chemical.

There was some charring if the paint on the cowling but mostly smoked up, and of course the air filter was toast. Threw filter away after inspecting for damage, got in a cranked it up and flew it home.

Second was was a Fuel injected Maule on floats at Jack Browns, as starting a float plane often has a greater sense of urgency because yiu could be being blown into trees or drifting down stream etc. They were showing the owner the flooded start procedure, intentionally flooding it. Well he burnt the Maule down to not much but a steel frame with floats.

I think it depends on severity, if the airplane burns up and the engine gets so hot seals etc are melted then I believe they are considered toast, but are the renuildable or which if any parts can be re-used.

‘I’d call Lycomings help desk, but think unless they have criteria it’s going to be at the discretion of the A&P

Edited February 22 by A64Pilot

[A64Pilot]

@PT20J

I got you beat on the car story.

It was a 1973 Ford F-250, during the first gas shortage My Father had saddle bag fuel tanks put on it because we were building a beach house in Fl and you could buy gas only on odd or even days based on your tag number and we couldn’t get home without the extra tanks, it had a fuel selector valve.

Well he would run it out of course, switch tanks and grind the starter until it started, second starter I put on it I put a Holley electric fuel pump on it connected to the ignition, told him turn the key on and when the pump quit rattling, crank it, which worked fine, no more burning up the starter.

A few years later the truck got older and became a Farm truck, it wasn’t maintained very well and I guess the oil bath air filter must have gotten dirty because one of the men had removed it who knows when. One day it backfired, carb caught fire, but I knew we were in trouble when I heard the pump start rattling and instantly we had a BIG fire, pump kept running until there wasn’t much left of the truck. I think it quit when the battery melted.

Bad thing was it was parked real close to the house but I was able to drag it away with the tractor before it caught the house on fire.

[M20F]

My guidance is put the fire out. 

[GeeBee]

While I was shopping for my R model I ran across two airplanes that had fire damage. It came from a back fire which ignited the fuel puddle underneath the main sump. I've made it a habit to move the airplane well clear of the puddle even if it has evaporated. Yeah, I know, you are not supposed to drop fuel on the ground, so sue me.

 

[PT20J]

Owner of the museum where I used to volunteer couldn't get the left engine on the B-25 started. Primed the hell out of it leaving a big puddle on the ground. Of course it backfired (well, actually afterfired) on the next attempt and lit off the fuel. Fortunately he got it started and blew out the fire just as the fire guard was running with the fire extinguisher. 

Ross, I think I'd just inspect everything closely -- too many variables to predict what damage might occur.

[hais]

13 hours ago, Shadrach said:

Folks,

I am looking for guidance on returning an engine to service after an engine compartment fire during a failed start.  No, I did not set my F model on fire. However, being a stone's throw from the fuel farm, I have seen my fair share of engine fires during start up.  The damage has varied from none to minor paint work. That being said, I can find no guidance from Lycoming or Continental on external and internal inspection protocol.  Your thoughts and experience appreciated.

The Poh for O says if you have fire while starting, continue to crank, and if it starts, continue to run it for a few minutes and then inspect for damage.

That sounds like they expect damages to be limited. 

Hopefully that will turn out to be the case with yours. 

[Shadrach]

Thanks for the feedback folks. And just to be clear, I have not nor have I ever set any plane afire. My question was driven by a trend I’ve seen recently of winter time engine fires from over priming and poor fuel atomization. Be careful out there.

[Pinecone]

On 2/21/2025 at 4:06 PM, 1980Mooney said:

The only engine fire that I have witnessed in 60 years was when 2 classmates tried to hand prime a V-8 w/ 4 barrel carb.   The rule was to always put the air filter back on before cranking.  Well one guy was pouring gasoline from a large paper cup into the carb throats as the other cranked the engine.  He poured too much gasoline in to start with, puddling on the closed throttle plates and in the intake runners. He was still holding the cup near the carburetor as the engine cranked, then immediately flooded as the throttle plates opened while still cranking and then a huge flame shot straight up.  The first guy, startled backwards, dropped the cup causing a second flare up.  Surprisingly he only got minor burns and engine was not visibly too burned.  But the hood of the car, which was up at about a 45 degree angle, had all the paint burned off the outside center part.

 

I did not witness this event, but dealt with it after.

My Parents had a 1963 Impala Station Wagon with a 327 4-bbl.  Supposedly this car does not exist, as they only put the 4-bbl on 64 and later.  Not sure how my Dad got it.  But there was a recall on the 64 and later for the plugs used to plug the passages where they were drilled, would fall out due to differing thermal expansion.  So this happened to this car.  A nice fire.  And my parents got to buy a new car THAT DAY.

But my Dad got the insurance company to give him a check and we fixed the car.  We had to replace the hood.  And some of the hoses and wiring. But that was it.  We had that car for another 6 or so years.

[1980Mooney]

4 minutes ago, Pinecone said:

I did not witness this event, but dealt with it after.

My Parents had a 1963 Impala Station Wagon with a 327 4-bbl.  Supposedly this car does not exist, as they only put the 4-bbl on 64 and later.  Not sure how my Dad got it.  But there was a recall on the 64 and later for the plugs used to plug the passages where they were drilled, would fall out due to differing thermal expansion.  So this happened to this car.  A nice fire.  And my parents got to buy a new car THAT DAY.

But my Dad got the insurance company to give him a check and we fixed the car.  We had to replace the hood.  And some of the hoses and wiring. But that was it.  We had that car for another 6 or so years.

It sounds much nicer than the 1962 Bel Air Station Wagon that we had with a 283 2-bbl.. I assume yours still had the 2-speed "Powerglide" slush bucket tranny.......  

[1980Mooney]

1 hour ago, Pinecone said:

I did not witness this event, but dealt with it after.

My Parents had a 1963 Impala Station Wagon with a 327 4-bbl.  Supposedly this car does not exist, as they only put the 4-bbl on 64 and later.  Not sure how my Dad got it.  But there was a recall on the 64 and later for the plugs used to plug the passages where they were drilled, would fall out due to differing thermal expansion.  So this happened to this car.  A nice fire.  And my parents got to buy a new car THAT DAY.

But my Dad got the insurance company to give him a check and we fixed the car.  We had to replace the hood.  And some of the hoses and wiring. But that was it.  We had that car for another 6 or so years.

BTW - we replaced the original miserly Rochester 2GC 2 bbl with the biggest 2 bbl available - a Holley 500 CFM 2 bbl.  I never really noticed any material difference for all the work (like many well-intentioned modifications on cars and planes!)  

[Pinecone]

This was the Rochester Quadra Jet.  So two small primaries with two HUGE secondaries.   Mild mannered, until you pushed the accelerator and opened those secondaries.

[AndreiC]

I had an engine fire happen in the first Cherokee I owned (a 140, carbureted O-320). (To be perfectly correct, the fire happened before I owned it ; but only by a few hours). This plane had been sitting for a while when I bought it, it had been inspected by a mechanic and had an annual inspection, but presumably did not get started at any point in the recent months before I went to buy it. 

I wanted to get checked out in it with a local instructor (I only had minimal time in Cherokees, mostly had trained in a 152), and when he and I tried to get it started it wouldn't start. We kept priming it, until we somehow managed to flood it; fuel coming out of the intakes (or carb, not sure) caught fire. We managed to start the engine and suck the fire in just as local people were running out with a fire extinguisher. The cowling was all metal; we took it out, looked at the engine inside, the local mechanic deemed it fine, and I flew it home after a couple of trips around the patch with the instructor.

(The guy was an old timer, and he alleviated my concerns by telling me that these "modern" engines are bullet proof, he never saw one fail, unlike the ones in the Piper Cubs he used to fly, which every once in a while required him to dead stick in a field to clean up the jets or something like that...) Seems like no damage was done in that fire, not even paint peeling on the cowling or anything. I flew that plane happily for a few hundred more hours with no incident. 

As an aside, I looked up the fate of that plane (N6085W) recently and it was very sad. Some years later the 70+ year old owner ran out of gas in it and crashed it, killing himself and his son who was in the right front seat. The rear seat passenger, the grandkid, survived with some injuries. Damn fuel exhaustion...