Carburetor Icing

N

njdem82

New Member
Hi All,
Ive just been doing some reading up on some issues that can come up during flight. One of the things that I almost never think about is carburetor icing. I think that one of the first indications of this would be a drop in RPM's and performance.

However it seeems that according to pilots it is a very subtle effect and very hard to identify the first time around (much easier the second time around). Considering the potential for hazard due to Carb Icing and the fact that it can happen at pretty high temperatures I wanted to ask if anyone has actually experienced this in flight or has heard alot on this subject?? If so what were the conditions and how did you/they initially notice it?? How did you isolate that as the problem , was it a matter of checklist usage or just common sense?? And finally how dramatic was the effect, did it happen quickly or was it a slow and cumulative effect over a (relatively) longer period of time?

So far I have not come across anyone who has experienced this or has even heard of it happen to someone , so I'm hoping that someone has experience with this (well I don't mean that I hope someone has had problems , just that they got through it --sounds bad when I put it that way) and has some advice on it
 
I searched the NTSB reports, in the last year alone there are 14 reports generated in the US. That's US only, and incidents that were reported.

I've had it, add heat and problem solved.
 
Heppened to me a few times. It seems certian airplanes are more prone to it than others. Where I used to work, you could almost gaurentee that if you were in the clouds, you were going to get carb ice in one particular 172. The rest, not so much. If you have the airplane trimmed for level flight, and it starts loosing altitude, and you haven't messed with anything, it's probably carb ice, so check with the carb heat. When it starts running like crap, LEAVE IT ON! Probably the most common mistake is to turn on the carb heat, get an engine that all of the sudden runs like crap(because it's now trying to run on water) and turn it off. It usually only takes a few seconds up to about a minute and a half for the ice to melt. And go full throttle to generate as much heat from the engine as possible if you do have ice.

Also, what I used to teach my students for the pattern was to turn on the heat well before the power reduction. Kind of like a "pre-emptive strike". Pre-heat the carb while the engine is making heat, not while you are at a reduced power setting.
 
Dear Lycoming and Continental:

Please leave the 1940s technology behind. How often do you have to think about carb heat in your car?
 
The best way to detect carb ice is to turn on the carb heat for a min or two and see what happens. Eventually you will find that you had some.
 
mshunter said:
Heppened to me a few times. It seems certian airplanes are more prone to it than others. Where I used to work, you could almost gaurentee that if you were in the clouds, you were going to get carb ice in one particular 172. The rest, not so much. If you have the airplane trimmed for level flight, and it starts loosing altitude, and you haven't messed with anything, it's probably carb ice, so check with the carb heat. When it starts running like crap, LEAVE IT ON! Probably the most common mistake is to turn on the carb heat, get an engine that all of the sudden runs like crap(because it's now trying to run on water) and turn it off. It usually only takes a few seconds up to about a minute and a half for the ice to melt. And go full throttle to generate as much heat from the engine as possible if you do have ice.

Also, what I used to teach my students for the pattern was to turn on the heat well before the power reduction. Kind of like a "pre-emptive strike". Pre-heat the carb while the engine is making heat, not while you are at a reduced power setting.
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Thats a very good point as with more power its safer and plus you will be more likely to detect a change. Another thing that I never really thought about was mentioned in a previous post that a dramatic reduction in performance when you turn carb heat on is going to make you want to turn it off again which would be the wrong thing to do. Just another one of those situations where you have to let your training or reasoning over power your initial reaction
 
Roger said:
Dear Lycoming and Continental:

Please leave the 1940s technology behind. How often do you have to think about carb heat in your car?
Click to expand...


Actually, in carb equiped cars, the carb heat is always on. See attached pictures, they are of a small block chevy intake manifold. The small port undernieth the carb flange is a heat riser, that heats the intake and carb to prevent icing.

quadra_jet_intake.gif


Second is a VW Type1 Dualport manifold. The pieces hanging off the bottom front (rusted) with the flanges are heat risers as well, to heat the intake and carb.

IMG_5126.jpg
 
I've had serious carb ice multiple times. I fly a lot of older aircraft.
In my experience, it comes on like somebody is chucking ice cubes at us. It really isn't the stealthy ninja attack that you think it may be. Twice though, the power reduced slowly, but typically vibration and pitch change gives it away without your eyes ever meeting the tach.

When you pull the heat on and it gets worse than it was, (you are eating that water) you know for sure it was carb ice. Let the carb heat run for a few minutes.

----
You know Roger, I love fuel injected engines, but I get an amazing satisfaction when lighting off a hot O-540. Let there be compression!
 
C-152- Subtle drop for a minute, then followed by a very dramatic drop and roughness. It gets ugly when the carb heat is turned on so hold on tight, and full throttle.

C-172- Pretty benign and cleans up quickly. Not a really serious drop ever.

C-182- Flew one for a while with an ice man ice detector. It was stupid annoying because the O-470 is an ice machine. We finally just got rid of the stupid thing because it was making us all skitso with its constant 'alarm.' The plane never really developed enough to cause the power to drop more than 1/2" or so.

C-150- If the relative humidity is higher than about .00001% you better watch out. Pulling the carb heat on seems to drop the power by about 92%, leaving you with about 8 belching horsepower and the sudden idea of an making an off airport landing. The 150 I flew made more ice than a slushy machine at 7-11.

Piper Warrior/Archer- There are supposed to not get ice and after a thousand or so hours I'd have to agree that it must be working.

C-172RG- The intake is buried deep in the cowling so I never bother with the heat and haven't had any problems with that.

Seminoles- Same agenda as with the 172RG.
 
Codyjp said:
C-150- If the relative humidity is higher than about .00001% you better watch out. Pulling the carb heat on seems to drop the power by about 92%, leaving you with about 8 belching horsepower and the sudden idea of an making an off airport landing. The 150 I flew made more ice than a slushy machine at 7-11.
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Yeah! I'd forgot about them! They were excellent "carb-heat-on-before-power-back" trainers.
 
CFI A&P said:
I searched the NTSB reports, in the last year alone there are 14 reports generated in the US. That's US only, and incidents that were reported.

I've had it, add heat and problem solved.
Click to expand...
Other good place to check for reports is the NASA ASRS database. There seems to not be a way to link to reports directly but two interesting ones are ACN 841103 and ACN 781305. You can plug the "Report Number" field here:
http://akama.arc.nasa.gov/ASRSDBOnline/QueryWizard_Filter.aspx

One involves carb ice on an instrument approach, the other en route.
 
Take a look at which of these airplanes, if any, are equipped with a pressure carburetor vs. a float carburetor. Tell me if you notice a relationship?


Codyjp said:
C-152- Subtle drop for a minute, then followed by a very dramatic drop and roughness. It gets ugly when the carb heat is turned on so hold on tight, and full throttle.

C-172- Pretty benign and cleans up quickly. Not a really serious drop ever.

C-182- Flew one for a while with an ice man ice detector. It was stupid annoying because the O-470 is an ice machine. We finally just got rid of the stupid thing because it was making us all skitso with its constant 'alarm.' The plane never really developed enough to cause the power to drop more than 1/2" or so.

C-150- If the relative humidity is higher than about .00001% you better watch out. Pulling the carb heat on seems to drop the power by about 92%, leaving you with about 8 belching horsepower and the sudden idea of an making an off airport landing. The 150 I flew made more ice than a slushy machine at 7-11.

Piper Warrior/Archer- There are supposed to not get ice and after a thousand or so hours I'd have to agree that it must be working.

C-172RG- The intake is buried deep in the cowling so I never bother with the heat and haven't had any problems with that.

Seminoles- Same agenda as with the 172RG.
Click to expand...
 
I've usually had it in Cessnas, but I did get it in a PA28-140 once. Felt weird to reach for the carb heat in flight in that plane.
 
I have expierienced Carb ice in a 150 before. I discovered it during the runup with my CFI. We followed Cessna's recomendations and started our takeoff run with carb heat on for about the first 1500 ft of runway and turned the heat off. the engine ran smoothly for the rest of the takeoff, so we proceeded and closely monitered the situation for the rest of the flight and all went just fine. It was a fairly minor case of carb ice (when we checked the carb heat, the engine didn't run too rough, the RPM just dropped and started rising indicating some carb ice was present, so obviouisly if the engine ran very rough we wouldn't have even started the takeoff in the first place). I haven't yet expieriened it in a 172 though...I live in the dry southwest, so it is relatively uncommon (though certaintly not unheard of) around here.
 
Only time I've actually gotten carb ice was during a maintenance runup on a Citabria when it was about 40 degrees and raining.
 
Roger said:
Only time I've actually gotten carb ice was during a maintenance runup on a Citabria when it was about 40 degrees and raining.
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I did get Carb Ice once in heavy rain while taxing. The plane nearly died. I just so happened to be giving the flight school owner a FR at the time too.
 
Hey I flew a GA7 cougar today for the first time and the IP told me carb heat is not really required for landing. I couldnt find the air intake filter for the engines and I was told it was inside the cowling. Maybe that provides suficient heat for the carb?

Engine on the plane is lycoming O-320
 
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