My CFI had his carb ice up yesterday...

Hobobiker

Hobobiker

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Nothing big for anyone here, but it made for a good story to use with his students. He was flying the A&P out east on Wednesday morning and was in the soup, totally IMC at around 5500. At one point he noticed manifold pressure had decreased a little, so he bumped it back up. About ten minutes later, he noticed that it had dropped again. He bumped it back up again, but kept an eye on it. About ten minutes later, the engine coughed. Not bad, but it was definitely something not normal for his plane. He looked over at the A&P and asked him what he thought it was. A&P had no idea. CFI decided to add some carb heat since he had noticed the manifold pressure dropping, and the plane coughed, spit, sputtered, puked, the plane shuttered some, etc....but then cleared right up and manifold pressure climbed.

Evidently he looked at the A&P and said "I think I'll keep the carb heat on until we descend", and all the A&P said, with very large eyes, was "I think that's a great idea..." LOL!
 
Hobobiker said:
Nothing big for anyone here, but it made for a good story to use with his students. He was flying the A&P out east on Wednesday morning and was in the soup, totally IMC at around 5500. At one point he noticed manifold pressure had decreased a little, so he bumped it back up. About ten minutes later, he noticed that it had dropped again. He bumped it back up again, but kept an eye on it. About ten minutes later, the engine coughed. Not bad, but it was definitely something not normal for his plane. He looked over at the A&P and asked him what he thought it was. A&P had no idea. CFI decided to add some carb heat since he had noticed the manifold pressure dropping, and the plane coughed, spit, sputtered, puked, the plane shuttered some, etc....but then cleared right up and manifold pressure climbed.

Evidently he looked at the A&P and said "I think I'll keep the carb heat on until we descend", and all the A&P said, with very large eyes, was "I think that's a great idea..." LOL!
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If it aint throttle creep, try carb heat.
 
Had that happen to me in a really light mist. Was on the descent into a small strip when the engine coughed back to life. Got my attention.

Good thing was had the engine not come back I had the strip made. Hurray for me.
 
Had it happen exactly once, in a J3 Cub.

Again, my first thought was "throttle creep", but eventually came to realize I had full power and rpm was down.

Full carb heat killed the engine (at fairly low altitude :eek:) and in spite of advice to the contrary it took partial carb heat to keep things running, at least at first.

When I landed, the carburetor was covered with frost on the outside, so very little doubt it was a real carb ice encounter.

BTW, this was out of Homestead General in S FL and it was not cold, a good reminder that carb ice is more a function of partial throttle and humidity than temperature.
 
Have only had it once in a 152 just after takeoff on multiple TNG's during training (CFI was on board) ... we live in the desert and were hitting an isolated "mist" only on base in the pattern.
 
I've only had ~7 hours of instruction several years ago, but I recall being told that any time I flew through a cloud to anticipate carb icing. Is that just an over generalization/simplification?
 
Dan Thomas said:
Sure is. Carb ice can happen in far more conditions than that, including bright summer days.

Dan
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Right. But he wasn't limiting it to just flight through clouds. He was saying it was much more likely to happen then, so any reduction in rpm in clouds should put carb ice high on the list of suspects.

I'm just wondering why the instructor in the first post wouldn't immediately reach for the carb heat to rule out carb ice. He was flying in clouds, in the fall ... seems like carb ice would be a highly likely suspect in those conditions. :dunno:
 
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comanchepilot said:
other than slowing down further in a mostly slow airplane to begin with?
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Even in my slowmobile, there are times that I need to reduce power in cruise. Instead of pulling back on the throttle to get to 2600 RPM couldn't I:
Pull the carb heat all the way out.
Pull back on the throttle to get it at 2600 RPM.
Set the mixture.
Readjust the throttle, if needed, to get back to 2600 RPM.

Jim
 
Rigged4Flight said:
Right. But he wasn't limiting it to just flight through clouds. He was saying it was much more likely to happen then, so any reduction in rpm in clouds should put carb ice high on the list of suspects.

I'm just wondering why the instructor in the first post wouldn't immediately reach for the carb heat to rule out carb ice. He was flying in clouds, in the fall ... seems like carb ice would be a highly likely suspect in those conditions. :dunno:
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He told me that this was his first experience with carb icing in over 800 hours of flight. As others suggested, the first time he noticed the manifold pressure drop he thought it might have been throttle slip/creep. The second time heightened his senses and that slight engine burp sealed the deal and he applied the heat.

To be very transparent, he's a great instructor/pilot and he NEVER lets me forget the carb heat check at runup, during the GUMPSS checks on downwind or before maneuvers, etc... Him sharing what happened, whether or not he may have diagnosed the issue slower than some other pilots may have, meant a lot to the students and was a good learning experience for us all - I'm betting even for him.
 
Hobobiker said:
He told me that this was his first experience with carb icing in over 800 hours of flight. As others suggested, the first time he noticed the manifold pressure drop he thought it might have been throttle slip/creep. The second time heightened his senses and that slight engine burp sealed the deal and he applied the heat.

To be very transparent, he's a great instructor/pilot and he NEVER lets me forget the carb heat check at runup, during the GUMPSS checks on downwind or before maneuvers, etc... Him sharing what happened, whether or not he may have diagnosed the issue slower than some other pilots may have, meant a lot to the students and was a good learning experience for us all - I'm betting even for him.
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I didn't mean to cast dispersions on the quality or character of his skills - I was just wondering if there was something I wasn't seeing or didn't know that would explain why carb heat in that situation wouldn't be one of the first things to try. At my stage of the game, I assume that my lack of knowledge/experience is to blame for most of the things about aviating that confuse me. :redface:
 
Rigged4Flight said:
I didn't mean to cast dispersions on the quality or character of his skills - I was just wondering if there was something I wasn't seeing or didn't know that would explain why carb heat in that situation wouldn't be one of the first things to try. At my stage of the game, I assume that my lack of knowledge/experience is to blame for most of the things about aviating that confuse me. :redface:
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No worries at all and I didn't take it that way. I'm a newbie, and he makes everything seem so smooth and easy, whereas I'm clunky and robotic in my motions. He makes it a habit to remind me to be, and I quote, "smooth, easy, and try not to scare the passengers..." LMAO!
 
Kiddo's Driver said:
Is there any reason not to use full carb heat to lower the engine RPM once you have reached cruising altitude?

Jim
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To add to what others have said, when you pull carb heat on, that typically opens up the alternate air source as well, so you are not filtering the air that goes into the engine at all. The reason it does this is to give you an option if you have impact ice. So, you have the problem that you are sending unfiltered air straight to the inside of your engine, which has some risk. Also, if you run carb heat on all of the time (and thus no filter), and then you get impact ice in that configuration, you have no out at that point.
 
PPC1052 said:
To add to what others have said, when you pull carb heat on, that typically opens up the alternate air source as well, so you are not filtering the air that goes into the engine at all. The reason it does this is to give you an option if you have impact ice. So, you have the problem that you are sending unfiltered air straight to the inside of your engine, which has some risk. Also, if you run carb heat on all of the time (and thus no filter), and then you get impact ice in that configuration, you have no out at that point.
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The unfiltered air is issue enough. In my configuration it would be exceptionally tough to get impact ice with carb heat on.

Jim
 
Dan Thomas said:
Sure is. Carb ice can happen in far more conditions than that, including bright summer days.

Dan
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And several folks have missed this very important fact. Visible moisture is necessary for structural icing, but NOT carburetor icing.

The carb has a venturi (and evaporating fuel) that lowers the temperature by up to 60 deg or so. All you need is a dewpoint higher than the carb temperature and the venturi below freezing. It can be a very clear warm day and still satisfy those conditions.
 
MAKG1 said:
And several folks have missed this very important fact. Visible moisture is necessary for structural icing, but NOT carburetor icing.

The carb has a venturi (and evaporating fuel) that lowers the temperature by up to 60 deg or so. All you need is a dewpoint higher than the carb temperature and the venturi below freezing. It can be a very clear warm day and still satisfy those conditions.
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They were in IMC, so moisture in the air was already understood.
 
Rigged4Flight said:
I've only had ~7 hours of instruction several years ago, but I recall being told that any time I flew through a cloud to anticipate carb icing. Is that just an over generalization/simplification?
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Yes. I spent almost five hours in clouds today and never had a hint of carb ice, despite ice accumulating on the windshield and airframe. But in similar conditions last spring I got it in one of the same airplanes I was flying tonight.

All to say, it's fickle, and you get it when you get it. Be aware of it and periodically check for it when conditions are ripe.
 
I had a similar experience several years ago while training for my IR. We were in a cloud in the 182 and manifold pressure kept dropping. I finally twigged on carb ice, added carb heat and after the stumbling quit (water through the engine really doesn't work well) the engine ran fine. We left the carb heat on for a while. Doesn't happen often, but often enough to explain why that knob is in the panel.
 
Ah yes: Icing time in the Northeast has arrived once again!!! Be careful when you apply carb heat to apply it and LEAVE IT on for a while. Had a friend pilot who was in the habit of constantly tweaking his carb heat a little here and a little there and all he did was to get some ice, melt a bit off, get more ice, etc. things came to a sudden and not so pleasant head (stumbling all over the place)and I convinced him to leave the freeking carb heat ON. His was not one of those engines known for making ice, and SOP was not to use partial carb heat. We were in and out of visible moisture, so clouds are not necessary as was stated before.
 
Of course, it might not be throttle creep OR carb ice. Flying along the coast of Albania a couple of years ago the engine started to cough now and then. I tried carb heat with no effect. Thinking that I should get to warmer air anyway, I descended, and in doing so I of course pushed the mixture in a little; the problem instantly vanished! I'd evidently flown into warmer air, or something, and that tiny difference had led to the mixture becoming just a little too lean.
 
Dan Thomas said:
Sure is. Carb ice can happen in far more conditions than that, including bright summer days.

Dan
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Yep. Margy and I were down at 2W5 where she was doing practice landings. We headed back home to VKX, now it's not very far so she kept a reduced power setting. About the time she hit the pattern the engine started to stutter. She just pointed it to the numbers and landed. After roll out I thought about it and asked her to put a little throttle in (standing on the brakes) and I pulled the carb heat. Sure enough. And I was told it was near impossible to ice up the PS-5C pressure carb. It was a shirt sleeve day.

The only other time I got carb ice was with a 172N. 50-ish day but very humid at IAD, just boiled off morning fog enough to be VFR. Thing iced up during taxi to the runway.
 
flyingron said:
The only other time I got carb ice was with a 172N. 50-ish day but very humid at IAD, just boiled off morning fog enough to be VFR. Thing iced up during taxi to the runway.
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I've had this happen, too, on a supposedly (according to another thread) ice resistant post-1967 172. It coughed at 400 AGL, right after takeoff. Not fun.

Really nice warm day, lots of aircraft waiting for departure, so an extended wait at low throttle after run-up.

On descent, carb heat does very little harm unless it's stupid-cold (where the heat is unable to get the carb above freezing). Unfiltered air is a concern, but not having a go-around when you need it is a vastly bigger concern.
 
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MAKG1 said:
...but not having a go-around when you need it is a vastly bigger concern.
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This is the main reason why our PA-28 GUMPSS check includes three seconds of carb heat on the downwind leg of each landing...cheap insurance.
 
Hobobiker said:
This is the main reason why our PA-28 GUMPSS check includes three seconds of carb heat on the downwind leg of each landing...cheap insurance.
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I try to pull mine (full on) when I pull power to descend, and I just leave it until I'm on the ground. So, it should be on for me already when I am doing my last configuration check on downwind.
 
I fly an Apache. They are known to make ice. Routine on entering the pattern is to pull on carb heat and immediately lean aggressively and reman that way until touchdown or going missed. I lean the mixture handles to a known position on the quadrant, a major advantage to knowing your airplane. I might skip this at 104 degrees in August, and I might not.

The fantasy about 'unfiltered air' is precisely that, a fantasy. All the filters do is keep the bugs and the clods from going through the carb. That nasty abrasive dust goes straight through no matter what position the carb heat handles assume.
 
FastEddieB said:
Source?
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Considering many of these filters trap smog particulate and I know people who had bad gaskets on their air filters diagnosed by silicon showing up in oil analysis I will run filtered air as much as possible.
 
Skylane81E said:
Considering many of these filters trap smog particulate and I know people who had bad gaskets on their air filters diagnosed by silicon showing up in oil analysis I will run filtered air as much as possible.
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I find that very hard to believe unless the filters are complete pieces of ****.

Those things are designed to flow A LOT of air with minimal resistance. If you're getting vacuum in the airbox, you need to change your filter a bit more often.
 
MAKG1 said:
I find that very hard to believe unless the filters are complete pieces of ****.

Those things are designed to flow A LOT of air with minimal resistance. If you're getting vacuum in the airbox, you need to change your filter a bit more often.
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Ever wonder how much dust and dirt is at 2000' ?

the only purpose of any aircraft air filter is to protect the engine while on the ground or nearly.
 
Hmmmn. IMC at 5,500. What's the matter with this....?
CFI to boot.

Otherwise it's a good story.... :)
 
MAKG1 said:
I find that very hard to believe unless the filters are complete pieces of ****.

Those things are designed to flow A LOT of air with minimal resistance. If you're getting vacuum in the airbox, you need to change your filter a bit more often.
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No, the oil analysis is just very very precise. Our oil analysis caught a tear in our 182 air filter exactly this way (increased silicon) but if you read the number of decimal places, the actual change is tiny. It still caught it. We didn't see it on preflight because it would line up and lay flat until you started the engine and sucked air through the tear.
 
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