Carb Ice - is there a prediction point where its a no-go?

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JasonM

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I was just thinking that the weather is looking prime for Carb Ice the next couple days and thought maybe I should check out a chart to see how bad it could be.

Well.. with a Temp of 61 F (16C) and Dew Point of 42 F (6C), this chart puts me at a Serious Risk for Carb Ice. http://www.atsb.gov.au/media/56519/carb_icing.pdf

Now, i'm just getting scared to go and fly. Seems to me that based on this chart, if I made a fly no fly decision, I would not be flying much at all.

Should I :

A. still fly and just plan on testing the Carb heat periodically for ice?

or

B. is there a point where I should just not be flying due to this chart?

or

C. Just fly as normal and be prepared to notice an RPM drop and act accordingly?

or

D. Do something else?

They are also calling for a chance of rain but the freezing levels are way above what I will be flying so structural icing is not a concern at this moment. Would the chance of rain effect this risk any more than what this chart is showing?
 
Use your carb heat occasionally....if you have a carb temp guage installed you'll see that its much less of a problem then you probably thought. I've had some carb ice in the C175 with an O320 but its been much less often than what I worried about. The carb temp guage is a neat thing....


frank
 
A and C are workable. And most folks use a combination of those two.
I have flown night over/along the Great Lakes at low altitudes due to icing in the clouds and you don't want to get behind on catching ice in the carb before it accumulates.
In those conditions I pull on partial carb heat until I get a power drop - this will be roughly half way, depending on the linkage and how the heat box flapper is adjusted - and then lean until the power/rpm/EGT comes back to where it was before I pulled the heat. I have flown several hours at a stretch with partial heat and leaned out. Happy engine/happy pilot. Keep an eye on the rpm/manifold/egt to pick up any change.

Pilots only get in trouble when they don't plan for ice and follow their plan.
 
BiffJ said:
Use your carb heat occasionally....if you have a carb temp guage installed you'll see that its much less of a problem then you probably thought. I've had some carb ice in the C175 with an O320 but its been much less often than what I worried about. The carb temp guage is a neat thing....


frank
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Thanks.. I was also watching videos and noticed this guy getting Carb Ice on a beautiful day. I'm not sure I would have expected that. My instructors always said it was highly unlikely unless the throttle was below the green arc. Will expect it more often now I figure. :)

 
Dr. O said:
A and C are workable. And most folks use a combination of those two.
I have flown night over/along the Great Lakes at low altitudes due to icing in the clouds and you don't want to get behind on catching ice in the carb before it accumulates.
In those conditions I pull on partial carb heat until I get a power drop - this will be roughly half way, depending on the linkage and how the heat box flapper is adjusted - and then lean until the power/rpm/EGT comes back to where it was before I pulled the heat. I have flown several hours at a stretch with partial heat and leaned out. Happy engine/happy pilot. Keep an eye on the rpm/manifold/egt to pick up any change.

Pilots only get in trouble when they don't plan for ice and follow their plan.
Click to expand...

I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
 
Go fly, keep a eye on your RPM, pull the carb heat every once in a while, remember if you have ice it will run ruff when you apply heat, if it does leave it be and wait for it to melt.

I've never canceled a flight or had a student cancel a flight or heard of anyone scrub a flight due to possible carb icing.

Also dont always run the carb heat, not going to get into all of it, but it's not needed and not really good for a couple reasons, just check it then turn it off

Go fly and have fun!
 
For those of us with carb temp gauges (I have one in the Skylane), what temp range is the yellow arc? One pilot said below 40°.

Another suggested a similar procedure as Denny with the explanation of "a bit of heat helps with the atomization of the fuel"
 
JasonM said:
I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
Click to expand...

It shouldn't build up with the temps from the carb heat, but I also know that an Apache's carb heat (what Denny flies) is more of a blowtorch than just some excess heat -- it's impressive.
 
JasonM said:
Thanks.. I was also watching videos and noticed this guy getting Carb Ice on a beautiful day. I'm not sure I would have expected that. My instructors always said it was highly unlikely unless the throttle was below the green arc. Will expect it more often now I figure. :)
Click to expand...

It was clear, and in the 90s on the ground, on the day that I got carb ice at 6500 MSL in cruise. :dunno:
 
AggieMike88 said:
For those of us with carb temp gauges (I have one in the Skylane), what temp range is the yellow arc? One pilot said below 40°.

Another suggested a similar procedure as Denny with the explanation of "a bit of heat helps with the atomization of the fuel"
Click to expand...

The 182 I fly for work has a digital one. We get the orange "danger zone" light below 40.
 
I, too, have a carb temp gauge in my 182. It's a nice thing to have. I removed the original to make way for the engine monitor install that also has a carb temp readout.

IIRC, there was an arc on the original gage and the "danger zone" was from 15*F to 40*F.
 
JasonM said:
I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
Click to expand...

That's the conventional wisdom. I wouldn't run partial carb heat without a carb temp gauge. If weather cools further after application of partial you might be helping it get to the freezing point, with fewer options if it forms.

I've had carb ice three or four times in 3,500+ hours. It is not something to lose sleep over or cancel flights over. Just be aware of it and check it periodically. If you've picked up some ice, full application of carb heat may result in a little roughness as the ice melts and water passes through, but then smooths out.
 
JasonM said:
I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
Click to expand...
Your old carburetor on your automobile ran with partial carb heat 100% of the time. There was a temperature sensor in the air cleaner that controlled a vacuum motor which controlled the air from the manifold shroud to maintain a minimum temperature.

If are in conditions where you ice with carb heat full on, then U B Skrewt no matter what. But I'm not aware of any actual case where that happened. (I can see where, in theory, if it is well below freezing and you are flying through precipitation the heat could warm up the ice / snow enough to melt it then it could re-freeze in the throttle body.)
 
Capt. Geoffrey Thorpe said:
If are in conditions where you ice with carb heat full on, then U B Skrewt no matter what.
Click to expand...

If the OAT is so cold that you are collecting carb ice with the heat full on, turning the carb heat off would likely stop the accretion of ice. Problem is, you can't melt the ice with warm air at that point. Hope you have enough power to maintain altitude for a bit, because you will have to wait for it to sublimate.

I believe I have seen some manufacturers list a minimum temperature limitation for carb heat, that is to say you should not apply carb heat when the temp is UNDER -15C or whatever. (Unless you need it for an alternate air supply if your air filter ices up). The reason is that -15C is too cold for carb ice to form, but application of carb heat will bring the temperature up to a level where ice can form.

I've never heard of anyone canceling a flight because of the possibility for carb ice. If you are concerned about it, re-read the POH and use the carb heat as directed, you'll be fine.
 
dell30rb said:
If the OAT is so cold that you are collecting carb ice with the heat full on, turning the carb heat off would likely stop the accretion of ice. Problem is, you can't melt the ice with warm air at that point. Hope you have enough power to maintain altitude for a bit, because you will have to wait for it to sublimate.
Click to expand...

Where is the moisture coming from if it's that cold?

The absolute humidity is going to be low because it is cold. When you warm it up, the relative humidity is going to be very low as well.
 
I've never heard of a flight cancelled due to the possibility of carb ice.

Some airframes are worse than others. Cessna 150 and older 182s are notoriously good/bad at picking up carb ice.

All the books say "don't run partial carb heat without a carb air temp gage."

Make sure your mechanic checks the whole carb heat system at annual....be there....help!
 
JasonM said:
Thanks.. I was also watching videos and noticed this guy getting Carb Ice on a beautiful day. I'm not sure I would have expected that. My instructors always said it was highly unlikely unless the throttle was below the green arc. Will expect it more often now I figure. :)

Click to expand...

It's the invisible moisture in the air that gets you...everyone is sensitive to icing when there are clouds. If the conditions are right, your carb can ice up on a clear blue day. Having said that, option A is the one to use; keep an eye on your tachometer, and if you notice a drop pull the carb heat. If you don't see a drop, pull it every 15 minutes or so just in case.

Bob Gardner
 
Capt. Geoffrey Thorpe said:
Where is the moisture coming from if it's that cold?

The absolute humidity is going to be low because it is cold. When you warm it up, the relative humidity is going to be very low as well.
Click to expand...

Not quite sure but I think I read it. Does anyone else recall reading in a POH not to use carb heat below a certain temp?

Perhaps if you pulled carb heat when flying through very cold clouds well below freezing while not picking up any airframe ice? The air heats up before it enters the carb, but then once passing through cools to a temperature slightly below freezing - the moisture condenses and forms ice on the carb.


Unrelated but the only time I ever picked up carb ice in flight I was skimming the tops of a layer in a 152 at a low cruise power setting and it was about 15C outside. Adding carb heat removed the ice.
 
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Capt. Geoffrey Thorpe said:
Your old carburetor on your automobile ran with partial carb heat 100% of the time. There was a temperature sensor in the air cleaner that controlled a vacuum motor which controlled the air from the manifold shroud to maintain a minimum temperature.
Click to expand...

No, every one I've taken apart turns of carb heat at wide open throttle. And they break, stick, or plug within a few years and are seldom repaired.

You may have a vacuum motor, but you have negligible vacuum at WOT.

The "partial carb heat" was generally regulated to around 80 deg F. If it was too cold to do that, you'd have full carb heat.
 
JasonM said:
I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
Click to expand...

If I recall correctly, Part 23 requires that full carb heat raise the temperature in the carburetor throat by 90 degrees. Hard to imagine how ice could build up with that amount of temperature increase. Flying with full carb heat just steals power from the engine...icing up with full carb heat is impossible, IMHO.

Bob Gardner
 
bobmrg said:
If I recall correctly, Part 23 requires that full carb heat raise the temperature in the carburetor throat by 90 degrees.
Click to expand...


We know that carb ice can form with OAT is around 70 degrees. If its -15F and you pull the carb heat, where does that put the incoming air temp?

I might be completely wrong about this as I can't find a reference right now.
 
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I had my warrior II cough on takeoff out of KOKC in November at night. Looong idling taxi followed by a quick takeoff. Carb heat was ineffective on the ground as engine compartment temperature was not sufficient to make the carb heat air do its job.

The icicles probably melted and detached as the engine compartment temperature increased to the point where the carb was warm enough. Not exactly a reassuring feeling. Being that the carb setup in the PA-28 is fairly warm bodied naturally, the cough was minor and cleared on it's own without the need for carb heat application on takeoff, where it's performance degrading anyways. It still did not make me happy. I'm quite pleased with the FI setup of the Arrow. I don't miss the carb. Hot starting has not yet been an issue for me.

The C-182 is just a poor carb setup. Way too throaty of an engine with too cool a carb location installation.
 
C -- fly normally, watch for the symptoms, and take immediate action if you see them. The nice thing about carb ice is that as long as you spot the RPM fall-off early, it's 100% curable with prompt application of full heat.
 
JasonM said:
I was told by another pilot not to run long duration with Carb heat on. Was told that if Ice builds up with the carb heat on you don't have any out. Is that a myth?
Click to expand...
If your carb heat is working properly, and you turn it on in response to formation of carb ice, more carb ice cannot form unless you pull the power so far back that the air through the muff isn't heated enough to keep the carb air temp above freezing -- and that's somewhere near idle power. Only a change in the conditions of flight (specifically, flying into air so cold that even the heated air gets below freezing in the throat) can cause carb ice to form with reactive carb heat left on, and in that situation, the unheated inlet air would have been so cold that any moisture in it was already frozen and would not stick in the throat so you would not have been using carb heat in the first place.
 
Ron Levy said:
If your carb heat is working properly, and you turn it on in response to formation of carb ice, more carb ice cannot form unless you pull the power so far back that the air through the muff isn't heated enough to keep the carb air temp above freezing -- and that's somewhere near idle power.
Click to expand...

But it should be understood that "working properly" is a relative term and varies greatly among different aircraft types. Some carb heat installations don't work worth a damn, due to their design - even if there's nothing "wrong" with them. The Champ carb heat with that crappy little heat muff is one that comes to mind. I swear it's practically useless.
 
RoscoeT said:
But it should be understood that "working properly" is a relative term and varies greatly among different aircraft types. Some carb heat installations don't work worth a damn, due to their design - even if there's nothing "wrong" with them. The Champ carb heat with that crappy little heat muff is one that comes to mind. I swear it's practically useless.
Click to expand...
Aircraft certified even as far back as 1949 under the original CAR 3 needed a 90F rise.
(a) Airplanes equipped with sea level engines employing conventional venturi carburetors shall be provided with a preheater capable of providing a heat rise of 90° F. when the engine is operating at 75 percent of its maximum continuous power.
Click to expand...
If your Champ isn't getting that, then you should have it repaired.
 
Ron Levy said:
Aircraft certified even as far back as 1949 under the original CAR 3 needed a 90F rise.
If your Champ isn't getting that, then you should have it repaired.
Click to expand...

Most of the Champs were built in '45-'46.
 
RoscoeT said:
Most of the Champs were built in '45-'46.
Click to expand...
CAR Part 4, eh? Can't find anything in there about carb heat. I'd suggest that if you don't have effective carb heat, you stay on the ground when the carb ice chart says carb ice is likely. But for any plane certified after 1949, if it isn't effective, it isn't meeting spec and should be repaired.
 
Ron Levy said:
Aircraft certified even as far back as 1949 under the original CAR 3 needed a 90F rise.
If your Champ isn't getting that, then you should have it repaired.
Click to expand...

+1

If your carb heat isn't working, get it checked and fixed if needed.

A few years ago there was story on a carbed 206, guy wasn't getting a drop for carb heat, launched anyways, turned out his airbox was coming apart, the 206 ingested a piece of the airbox that rattled off causing a engine failure. I don't recall any fatalities, plane was totaled though.
 
I do not recall ever worrying about carb ice in the Cherokee flying vfr. this must be a high wing thing....
 
I'm always amused by those who mumble darkly that they heard that doing this or that for an extended period is bad for your engine, or that it leaves you no way out.
I can also tell you I have been in wet snow, at night, with a load in the cargo hold where full carb heat and leaning aggressively to recover power was the only method to keep from going down into the Appalachians. I never was so happy to finally clear the mountain and begin the dive down to Greenville-Spartanburg.
And the fellas I hung with who were freight dogs did the same in the same conditions. One night we went into ORD with a load of auto parts where the props on the D18 were flinging chunks of ice against the fuselage and thumping the side of my calf - bang - bang - all the way across Lake Michigan at 1:00 AM. And you can bet the carb heat was full on and the mixture pulled halfway to cutoff to keep those engines hot.

Now, for the OP - those were extreme conditions that you will never go out in. Just make a plan and fly the plan and you will be fine. No one ever died from using carb heat in icing conditions. But a bunch sure have for not using it.
 
Tony_Scarpelli said:
I do not recall ever worrying about carb ice in the Cherokee flying vfr. this must be a high wing thing....
Click to expand...
You may not have worried about it, but it happens in Cherokees all the time. The location of the wing has nothing to do with the likelihood of carb ice forming. OTOH, the design of the induction system does, and Cherokees with their Lycoming engines with the carb bolted to the bottom of the sump full of warm oil are less likely to have carb ice than 1950's-1960's Cessnas with Continental engines where the carburetor is mounted differently and thus receives less conduction heating from the engine itself. Put a Lycoming in a high-wing Cessna, as Cessna started doing in the 172 in 1968, and the likelihood of carb ice lowers to about the same as with the same design engine in a low-wing Piper/Grumman. It still happens, but it takes more severe conditions to do so.
 
Ron Levy said:
You may not have worried about it, but it happens in Cherokees all the time. The location of the wing has nothing to do with the likelihood of carb ice forming. OTOH, the design of the induction system does, and Cherokees with their Lycoming engines with the carb bolted to the bottom of the sump full of warm oil are less likely to have carb ice than 1950's-1960's Cessnas with Continental engines where the carburetor is mounted differently and thus receives less conduction heating from the engine itself. Put a Lycoming in a high-wing Cessna, as Cessna started doing in the 172 in 1968, and the likelihood of carb ice lowers to about the same as with the same design engine in a low-wing Piper/Grumman. It still happens, but it takes more severe conditions to do so.
Click to expand...

But still, Piper didn't take carb ice as seriously as Cessna, and I can see no reason why they didn't. There is no substantial difference in the engine, though the exhaust system is larger in the Cherokee and takes up a lot more of the space under the engine and maybe heats it more. The Cherokee 180 I did some of my training in way back in '73-'74 didn't mention carb heat on the pre-landing checklist, nor did the Comanche 250 I flew many years later. Cessna always had it there in print.

I have seen carb ice often, in 172s, on nice summer mornings when the dewpoint is high enough. The students would go out and start up, let it idle for a few minutes to warm up, and when they closed the throttle after positioning the airplane for a runup the engine would try to quit. They would just open the throttle a bit rather than think about what the engine was trying to tell them: that there was ice forming already. The oil sump is still cold on the first startup of the day. There have been some accidents where an airplane took off after a lengthy taxi, and crashed because it couldn't climb out of ground effect. The carb had iced up during the taxi after the runup, and Lycomings will do it as handily as a Continental until that sump gets hot.

One never dives into the water without knowing how deep it is, what's under the surface, and what its temp might be. But many take off into the blue without knowing what the atmosphere's properties are at that moment. So carb ice sometimes gets them.

Dan
 
Hmm.. I wonder if...

One day a few weeks ago during the run-up, when I pulled the carb heat to check for a drop in RPM, It was a huge drop compared to normal. I remember saying "wow, that was a big drop for the carb heat check". Normally I get about 25-50 rpm drop in the cessna 172. That day I saw about 175-200 rpm drop. I remember thinking that it must be working "Really" good today to do that and went about my checks and took off without any problems.

I wonder if the carb had formed ice pre run-up that afternoon? Luckily didn't have any issues on take off.

Was this a sign of something else? Man it stinks being a low hour PP. So much to learn.
 
JasonM said:
Hmm.. I wonder if...

One day a few weeks ago during the run-up, when I pulled the carb heat to check for a drop in RPM, It was a huge drop compared to normal. I remember saying "wow, that was a big drop for the carb heat check". Normally I get about 25-50 rpm drop in the cessna 172. That day I saw about 175-200 rpm drop. I remember thinking that it must be working "Really" good today to do that and went about my checks and took off without any problems.

I wonder if the carb had formed ice pre run-up that afternoon? Luckily didn't have any issues on take off.

Was this a sign of something else? Man it stinks being a low hour PP. So much to learn.
Click to expand...

It was a sign of something else, probably. If it was carb ice, the RPM should have recovered after 15 or 20 seconds with the heat on. If it didn't I'd suspect a collapsing carb heat hose. There's a chunk of 2" SCAT hose, about 18" long, between the heat muff and the carb airbox, and the wire inside it can come loose and fail to support the hose internally. Air moving through it sucks it shut and can shut the air off entirely in a bad case.

Needs checking.

Dan
 
Dan Thomas said:
It was a sign of something else, probably. If it was carb ice, the RPM should have recovered after 15 or 20 seconds with the heat on. If it didn't I'd suspect a collapsing carb heat hose. There's a chunk of 2" SCAT hose, about 18" long, between the heat muff and the carb airbox, and the wire inside it can come loose and fail to support the hose internally. Air moving through it sucks it shut and can shut the air off entirely in a bad case.

Needs checking.

Dan
Click to expand...


Will do. thank you sir.
 
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