Carburator Fire
 

I could not start up the Cessna 152 with the cold, i did all the procedure's that are in the POH for cold starting operations but no luck!

So i called in the tech guy, he came with his battery, he just told me, apply the brakes and did all the starting himselfs, the engine fired up loudly with white smoke comming out of the cowling, he just yelled at me, don't worry, you just had a carburator fire, you can go fly now! Wich i did.. the engine runned smooth and normal but the plane did go into the tech hands after my flight, he told me to check the battery etc...

But is that correct ? Isn't a carburator fire/backfire dangerous ? In my books i read that carburator fire could result in killing the carburator completely ?

if it killed the carb, surely it wouldn't run?????

where was the fire? contained inside the intake/exhaust?

backfiring on its own is not dangerous. it can cause stuff to blow off (intake ducting etc) but if it's bad enough to cause damage, your engine won't run.

standard "engine fire on startup" procedure in thye POH of one of my aircraft is "continue cranking the engine" - this supposedly uses the excess fuel up.

Presumably fire on startup is less likely with a fuel injected engine.

Merry Xmas Sternone!

SB

On the ones I fly too. If the fire is somewhere in the intake system, then this sucks the fire into the engine, where it can't do any damage.

But the next items are: shut everything off and evacuate, if possible taking the fire extinguisher with you. Not: go flying as if nothing happened.

Sternone, if you were not happy with what happened (and the way I read your post, you weren't), you should not have accepted the aircraft and gone flying. That's what command authority is all about. Taking the cowling off and giving things a good look over will only take a few minutes and you already had the tech guy around.

As for taking off with a suspicious battery, well, it's not dangerous per se in one of those old spamcans. But it would be a nuisance if you had to shut the engine down somewhere (on a landaway, for instance) and would not be able to start it again. Then again, it might just have been a cold and slightly depleted, but otherwise perfectly healthy battery. You do keep your walkaround, with lights flashing, pitot heat burning etc. as fast as possible, don't you?

Sternone, why are you asking something as basic as this? I've read your previous posts - thought you knew everything. :rolleyes:

Oh No! its the do list!
 

Most intake fires are due to the time between priming and starting the engine, this time gap gives the fuel that the primers put into the inlet system just upstream of the inlet valves to run down into the air intake and pool in the lowest part of the system.

The root of the problem is in the way most instructors teach the use of the check list.

Most of the students that I seen use the check list as a "do list".

It should take about ten seconds between priming the engine and turning the starter and another twenty seconds to check the oil pressure is increasing, the starter relay light is out (if fitted) and the engine is stable at 1200 RPM.

Only when this has been done and you have checked that the aircraft is not moving should the check list come out to check that all the required items have been done.

All the engine start actions from priming untill the engine is is at a stable idle speed should be "memory items" (or recall items in Boeing speak) this cuts down the chances of an intake fire to almost nill.

If you use the check list as a do list you are setting yourself up for an intake fire each time you start the engine.
The rest is down to luck most of the time the engine will start without a problem but if you have a backfire you will have an intake fire and if you are very unlucky you will destroy the aircraft.

Both the POH and the checklist with your aircraft will have a procedure set out for how to deal with an engine fire (usually involves carrying in cranking until the excess fuel is sucked through the engine) and you really should be familiar with this quite early on in your training.


I would humbly suggest that more time spent studying some of these basic procedures and less time spent in chatrooms talking about aircraft falling to pieces in flight and suchlike will help you stay alive to learn some of the more complex stuff for yourself.

Fires after starting fuel injected engines can be a problem IF the happless pilot overprimed the engine(s) prior to actually starting the beast.
Puddle of fuel underneath...wooosh, up it goes.
I personally watched a CE401 do this many years ago...after the inferno there wasn't enough left of the aeroplane to fit in a shoebox.
Ashes...totally:uhoh:

Hi Sternone! I flew the plane after you. Also had a flat battery, also needed the tech guy to start it up after backfiring. Altough the tech guy also told me (which I did not know and was never told by the instructors) to wait at least 10 seconds between priming and starting the engine (although sometimes it feels like it takes me at least 10 seconds just to lock the primer after using it :ugh:). So, as someone mentioned in a post, it should be a memory list rather than a "do" list. Have you flown the plane since? more worrying was that roll/yaw tendency of the plane...
Merry Christmas!

Hi there :-) The 10 seconds is to let the fuel vaporise a little so it fires up more easely, that type of engine is just not easy to start in cold weather...

the roll yaw should have been fixed by adjusting the fixed rudder trim, it was indeed looking a bit to the wrong direction ... ;) it was the rudder since if it's wrongly trimmed it goes into a roll...

I was a bit worried about the huge amount of white smoke and smell that came out of the engine compartment, but most blokes above seems to be ok with that carburator backfiring...

wsmempson and ShyTorque are just paid members of my fan group, it makes PPrune loads of fun!

I have never flown a C152, but in other equally small planes (DR200-120 for instance) the big bloke in the RHS makes all the difference. So you're flying dual, no roll/yaw tendencies at all. Perfectly balanced, hands-off. But when you fly solo, continuous pressure on the stick or yoke is required to keep the plane level and balanced. To relax your arm muscles every now and then, you can keep the airplane level with a bit of pressure on the rudder, but the aircraft won't be perfectly balanced then.

If you have an in-cockpit adjustable rudder or aileron trim it will help a lot (although the rudder trim in the PA-28 seems to be next to useless in this respect) but otherwise you'll just have to deal with it.

In general most clubs/schools seem to have a policy not to fiddle with fixed trim tabs at all, since you're likely to make things worse rather than better, unless you actually do a comprehensive flight test program consisting of multiple short flights to evaluate balance, with tiny adjustments in between, over the whole loading range. Not something the average student/renter is willing to undertake.

(Wow, eleven posts in a sternone thread and nobody has mentioned the M-word yet!)

You weren't worried enough...

Yes the engine ran after the fire, and that fact was the reason that the fire did not continue to do damage, but it might have already done so.

Writers here have given lots of wisdom about how a carb fire could have started, and keeping cranking is the best way to get it out. BUT....

Once you are satified that the fire is out, and the engine is running smoothly, shut it down - you're not going flying. And forget about charging the battery with the engine, that's what chargers are for!

The carb contains a jet and a venturi (remember ground school?) The venturi in particular is a rather delecate metal part which can be damaged by fire. Such damage could result in it being deformed, and not providing proper fuel distribution, or worse, breaking off inside, and being drawn up into the induction system later in the flight. You'd be gliding then!

Once you know that there has been a carb fire, tag the aircraft not fit for flight until inspection. Only a disassembly and inspection of the carb can assure that it has not been damaged.

Were you to take the aircraft flying uninspected after the carb fire, and it quit because of carb damage, the resulting forced landing might not be entirely your fault, but you'd still be the guy who put it in! (And there'd be a lot more cost and delay than just the carb inspection)

For all of the chatter I've read on this forum about the rights of the the next pilot to fly an aircraft which has not been subjected to an unreported unusual event by the last pilot, the possible damage from a carb fire is right up there in dangerous things to not report, and have inspected.

I have disassembled Cessna 150 carbs (which are a little different for 152 carbs) and found that they were not safe for flight, because of carb fire damage. but the engine did still run.

Nice going asking, instead of telling us!

Pilot DAR

Come on Shy--those sort of comments put people off asking questions.

Any engineer worth his salt would at least take the cowlings off after a carb fire and do an inspection.

I always thought the 10secs was to allow the excess fuel to drain away, not sure how it vaporises in cold weather very well after you stop pushing the primer. We used to prime six pull the prop through 4 revolutions (mags off!!) another 4 primes and start. The secret of getting the ones going I am come across seems to be over priming, even priming while starting.

I wonder Sternone if you knew where the nearest external fire extinguiser was while you were doing all this. Before starting precautions--always check the position of the nearest external fire extinguisher.

Sternone you stay on here because if you ever become an instructor it will give you a good grounding for how not to deal with people.

If you have a carb fire on the Cessna 150/152 good chance you have set fire to the air filter. Any excess fuel will pool at the lowest point which is the carb heat box/valve assembly. Fuel will be forced to run towards the oil soaked filter and if blow back occurs this will catch fire. Carb heat box has a hole in bottom so most fuel should drain out onto the nose wheel.

In winter i usually start the engine before the students/PPL's get their hands on it. Mixture rich, carb heat to hot posn so the engine can breath easier, couple of primes then third stroke of the primer as i crank the engine.

Of course this assumes that the priming lines are all connected and the jets unblocked.
Club using a Cessna at moment with only one primer line plumbed in to one cylinder, fortunately the a/c carb is fitted with an accelerator pump so several pumps of the throttle AS THE ENGINE IS BEING CRANKED, gets it started.

BEB you just reminded me the early C152 engines carbs did not have accelerator pumps and were a pig to start in cold weather.

Known many blow backs but never experienced that

Mine doesn't has an accelerator pump, i always have to say that to the FI's who are pushing the trottle in and out rather quickly while starting, some didn't believe me and i had to show them the POH hehe

There is your probelm, he he

Have you tried Easy Start, spray it on the instructor?

Sternone said: Yes, I sometimes enjoy baiting folk as much as Sternone does with style; nice to see that he can take it as well as dish it out!! :D

So, Llanfairpg, I don't think Sternone will be put off that easily; read some of his "previous". :E

It's called banter, btw.

Sternone, if the air filter has got singed, it may restrict airflow at full power so the next takeoff might be interesting, to say the least. If a supply pipe gets weakened by heat, or a wiring cable, it may fracture later, which might make the landing interesting.

:D :D :D Nice to see you have seen the light at last Sternone. :ok: The C152s I fly at the moment are treated very nicely and tucked up every night nice and warm in the hangar, summer and winter. :ok: Needless to say I haven't had a problem starting one even with the temperature at -3.5C. (I know that's not as low as some people have to put up with) The one I learned to fly in spent most of its life outdoors come hail, rain, sunshine or snow and I can only recall two occasions when it refused to start and it was necessary to get the engineer out to it. :ok:

Sternone, please make sure the tech has a thorough check of the carb before you fly next time. As for me, I think that I became a bit too worried last time when the CFI told me that he would like to see this plane gone...:sad:

:D:D:D

backpacker: the roll/yaw scenario I was reffering to in my previous post was something different than just an empty RHS. Last time I took off (solo indeed), as soon as the plane was off the ground it just started banking quite strongly to the left. I've never had that before and it made for quite a hair raising experience where at about 400ft I was waaaaaaaaay to the left of the runway even with a wind from the left! Left the circuit and had to fly with constant heavy foot on the right rudder. Made for an interesting landing also:bored:. (sorry Sternone, don't mean to hijack this thread..)

nanocas, no problem ofcorse, the question is, who is going to fly this bird first ? I would rather have the tech guy fly it a circuit to see the rudder trim is set correctly, but there's gonna be some really good preflight check from my side before i fly!!

Well, if it's that bad, then the plane should be grounded immediately to check what's wrong. And to let a student take the first flight after those kinds of problems, that would be grossly irresponsible.

Sternone/nanocas, there's an additional pre-flight check that I was taught when starting my aerobatics course. While doing the walkaround, once you've arrived at the rudder, walk back from the aircraft a meter or two. Squat down low so that the top of the main wing almost, but not quite disappears below the top of the elevator. The place where those two top lines intersect should be exactly the same, assuming you are squatting exactly in the aircrafts centerline. This is a very effective, yet very simple check to see whether the aircraft hasn't been bent somehow. I don't know any other check that you can perform as a pilot without taking out a spirit level and the book with tolerances.

There can be many reasons why an aircraft flys one wing down but thats why we have licensed engineers. Or I should say hopefully thats why we have licensed engineers, write it up in the technical log if only to cover your own backside.

I've noticed that with C152s that are in the habit of flying along out of balance opening the window can put them back in balance. Saves having to fly along with your foot pressing down on the peddles.

Also makes it easier to give hand signals

Backfiring is dangerous, and yes it can blow off the induction, carburetor, etc...it can also set fire to the inlet filter, cowling interior, etc. It can cause damage to intake components, cause induction leaks, and consequently cause uneven lean mixtures which can result in engine damage or engine failure.

An afterfire makes a bang out the exhaust. A backfire makes a bang out the intake. After excess priming, it can set a fire that you're not going to suck back into the engine.

If you've had an engine fire, you certainly don't need to go flying. You need to have a qualified mechanic pull the cowl and perform an inspection. This is common sense. I say this as a pilot, mechanic, inspector, and instructor.

Your battery was dead. Your aircraft was unairworthy. The battery shouldn't be charged in the aircraft; you'll find that in both the aircraft flight manual, and in the maintenance manual. Depleted batteries being charged create heat, and explosive gasses. You don't know why the battery is dead, and the fact that it's dead could be a short, could be a bad battery, could mean you have other electrical faults. If you have faults in the airplane, correct them, learn why they exist, before you fly.

What's a "carburator"?

car·bu·re·tor [kahr-buh-rey-ter, -byuh-] Pronunciation Key - Show IPA Pronunciation
–noun
a device for mixing vaporized fuel with air to produce a combustible or explosive mixture, as for an internal-combustion engine.
Also, car·bu·ra·tor, car·bu·ret·er; especially British, car·bu·ret·tor, car·bu·ret·ter [kahr-byuh-ret-er] Pronunciation Key - Show IPA Pronunciation.

[Origin: 1860–65; carburet + -or2]
Dictionary.com Unabridged (v 1.1)
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.

EDDNR,

The carburator is the bit at the front of the C152 where the flames come out from.

Gosh, I always thought the bit at the front was the air intake and the propellor.

It's only at the front AFTER the flames have come out of it.

Thanks, Llanfairpg, now I know why you're an instructor.

Mind you, I've never seen flames coming out of a propellor and I thought the bit right at the front is the spinner. :bored:

Well you are cleverer than I am, because I am still trying to puzzle that one out!

Just a thought.

You've had a fire, you aren't being paid to fly - you are paying to fly, there's a maintainer there next to the aircraft.

Just what reason is there to actually fly until the maintainer has check the carb and made a tech-log entry stating that he considers the aircraft fit for flight? Damned if I can think of one.


It's a matter of doubt. If there is ANY doubt about the fitness of the aircraft to be flown, get it checked. The carb is PROBABLY okay, but probably isn't definitely!

G

The one cold start engine fire I had in a C172 I had them pull the cowl & check it. This was a cold day, rental airplane, and I didn't think it was going to start & suck the flames in so I got out the C02 fire extinguisher. I learned a couple things from the experience:

1) If your airplane has an accelerator pump, don't be pumping the throttle because the excess fuel in the induction system can catch fire!
2) In cold weather prime before you begin your preflight.

-- IFMU

IFMU
 

If you prime before you do the pre-flight were exactly do you think that the fuel goes wile you are walking around checking the aircraft?

Also can you tell me why the primer nozzels are fitted near the inlet valves?

I'm gonna fly the bird right now, let's see what it gives!!

Of course it flows down through the induction tubes to the carb, due to gravity. Along the way some of it also becomes vapor. Vapor is good when it comes to starting and running the engine. If you pump the throttle it all ends up in the airbox, unless the engine is spinning round enough to pull it up.

That's what I think.

-- IFMU

IFMU
 

Clearly you don't understand the construction of your engine, If you pump the primer and then leave the aircraft all the fuel will run down into the airbox.

The practice of priming the engine and then doing the walk round inspection is just a good way of setting up your self for an intake fire.

Please read my first post before you set fire to an aircraft and maybe yourself.