I think I got some carb ice yesterday...

tawood

tawood

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Tim
Took an hour long flight with my girlfriend to Put-In-Bay yesterday. Weather was hazy/humid 80+ degrees, and we flew through a couple of very light rain showers (more like sprinkles) on our way there. When I started our descent to Put-In-Bay, I pulled my throttle from 2400 rpm cruise to about 1900 rpm and as I did the engine became very rough, with a moderate vibration (of course this had to happen while we were over Lake Erie). I pulled carb heat and advanced the throttle back to 2400 rpm which smoothed it out. I kept us at 2400 until I was sure we could glide to the field, then pulled back to 1900 again, and this time everything was fine.
My Cherokee 140 POH doesn’t call for regular carb heat, saying something like “when necessary”...I think I discovered when “necessary” is...One thing I was expecting with a carb ice encounter that didn’t happen: I’ve heard of engine vibrations getting temporarily worse when carb heat is first applied (as the ice melts), but I only noticed things settling down after carb heat. Or, could it have been something else? I don’t know..I do know we had no problems on the hour flight home.
 
I've had very mild induction ice a couple times in my Archer. Living in humidity central, it was not unexpected. I got in the habit of cracking open the carb heat a little bit on descents at low power. In cruise if rpm slowly changed or I heard a good burble, I'd give it 30 seconds of full heat just in case.
 
Unit74 said:
I've had very mild induction ice a couple times in my Archer. Living in humidity central, it was not unexpected. I got in the habit of cracking open the carb heat a little bit on descents at low power. In cruise if rpm slowly changed or I heard a good burble, I'd give it 30 seconds of full heat just in case.
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Partial carb heat can be dangerous under some conditions. If you "just barely" melt the ice it will be sucked further into the induction system and re-freeze where carb heat can't melt it. Carb heat should be full on or full off. Anyhow that is how I was taught. -Skip
 
tawood said:
Took an hour long flight with my girlfriend to Put-In-Bay yesterday. Weather was hazy/humid 80+ degrees, and we flew through a couple of very light rain showers (more like sprinkles) on our way there. When I started our descent to Put-In-Bay, I pulled my throttle from 2400 rpm cruise to about 1900 rpm and as I did the engine became very rough, with a moderate vibration (of course this had to happen while we were over Lake Erie). I pulled carb heat and advanced the throttle back to 2400 rpm which smoothed it out. I kept us at 2400 until I was sure we could glide to the field, then pulled back to 1900 again, and this time everything was fine.
My Cherokee 140 POH doesn’t call for regular carb heat, saying something like “when necessary”...I think I discovered when “necessary” is...One thing I was expecting with a carb ice encounter that didn’t happen: I’ve heard of engine vibrations getting temporarily worse when carb heat is first applied (as the ice melts), but I only noticed things settling down after carb heat. Or, could it have been something else? I don’t know..I do know we had no problems on the hour flight home.
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I dunno, it doesn't really sound like carb ice to me. Generally, if you get carb ice, right when you turn the heat on the engine will cough and sputter briefly while it ingests the slug of ice/water you just released from the carb. It's very quick, though - The first time it happens, you'll immediately regret putting on carb ice because you think it caused the engine to fail, but by the time you even think to turn the carb heat back off, the engine will be running better.

Is it possible that you got a bunch of rainwater in the air filter and the induction was being less than efficient at the time? Carb heat would bypass the filter and make it run better, and then in a little bit it'd work better again. I've never experienced that, but I'm trying to think of what else it could be.

Of course, your description of what happened sounds like you may have had it and not expected the engine reaction the way it really happens. "I’ve heard of engine vibrations getting temporarily worse when carb heat is first applied (as the ice melts), but I only noticed things settling down after carb heat." It's only VERY temporary, as I described above. Maybe a second or two, and then it'll smooth right out. The way you applied carb heat and added power right away, well, I would expect that the engine would smooth out before you even got your hand to the throttle unless you were in a bit of panic-mode and did it really fast.

You were in the zone with potential for it:

carb-ice-potential-chart.jpg
 
I think it was carb ice and I think tawood handled it perfectly. Carb heat is also alternate air for most piston AC that have carb heat. So it could have been rainwater partially blocking the aircleaner but I tend to doubt that.
 
flyingcheesehead said:
I dunno, it doesn't really sound like carb ice to me. Generally, if you get carb ice, right when you turn the heat on the engine will cough and sputter briefly while it ingests the slug of ice/water you just released from the carb. It's very quick, though - The first time it happens, you'll immediately regret putting on carb ice because you think it caused the engine to fail, but by the time you even think to turn the carb heat back off, the engine will be running better.

Is it possible that you got a bunch of rainwater in the air filter and the induction was being less than efficient at the time? Carb heat would bypass the filter and make it run better, and then in a little bit it'd work better again. I've never experienced that, but I'm trying to think of what else it could be.

Of course, your description of what happened sounds like you may have had it and not expected the engine reaction the way it really happens. "I’ve heard of engine vibrations getting temporarily worse when carb heat is first applied (as the ice melts), but I only noticed things settling down after carb heat." It's only VERY temporary, as I described above. Maybe a second or two, and then it'll smooth right out. The way you applied carb heat and added power right away, well, I would expect that the engine would smooth out before you even got your hand to the throttle unless you were in a bit of panic-mode and did it really fast.

You were in the zone with potential for it:

carb-ice-potential-chart.jpg
Click to expand...
Kristine and I were filming for our blog at the time, so I’m gonna have to review the video again, but my recollection was I reduced power, the engine became very rough, and after maybe 5 seconds of rough running, I pulled carb heat. Over the next five seconds, the engine gradually smoothed out, and then I added power. Oh, and during that 10 seconds, I did a lot of swearing, lol, while Kristine said, “What? What? What?” She said later she didn’t notice anything, which I was surprised because I couldn’t imagine how it could be missed, as it vibrated pretty bad for 5 or so seconds.
 
tawood said:
Kristine and I were filming for our blog at the time, so I’m gonna have to review the video again, but my recollection was I reduced power, the engine became very rough, and after maybe 5 seconds of rough running, I pulled carb heat. Over the next five seconds, the engine gradually smoothed out, and then I added power. Oh, and during that 10 seconds, I did a lot of swearing, lol, while Kristine said, “What? What? What?” She said later she didn’t notice anything, which I was surprised because I couldn’t imagine how it could be missed, as it vibrated pretty bad for 5 or so seconds.
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Usually and typically I respond to vibration. Lol. I felt nothing.
 
Skip Miller said:
Partial carb heat can be dangerous under some conditions. If you "just barely" melt the ice it will be sucked further into the induction system and re-freeze where carb heat can't melt it. Carb heat should be full on or full off. Anyhow that is how I was taught. -Skip
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Yea, I agree on that. I really didn't know what I didn't know. I never had any issues though, so who knows if it was a bad idea. I'm injected now so a moot point.
 
I seriously doubt it was rainwater in the air filter as we only flew through sprinkles, maybe 20 minutes prior. I have flown this plane through downpours in the past without issue.
 
Skip Miller said:
Partial carb heat can be dangerous under some conditions. If you "just barely" melt the ice it will be sucked further into the induction system and re-freeze where carb heat can't melt it. Carb heat should be full on or full off. Anyhow that is how I was taught. -Skip
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Yes full on if you suspect carb ice, and after it has melt and engine running smooth again, one may then use partial carb heat as a precaution for any additional ice.
 
What if you don't suspect it, but want to keep it from happening though. That was my position with partial carb heat. Raise the ambient air temp in the induction to keep it from happening. If you suspect it, full on till it clears up. Then a few min more for good measure!
 
tawood said:
Took an hour long flight with my girlfriend to Put-In-Bay yesterday. Weather was hazy/humid 80+ degrees, and we flew through a couple of very light rain showers (more like sprinkles) on our way there. When I started our descent to Put-In-Bay, I pulled my throttle from 2400 rpm cruise to about 1900 rpm and as I did the engine became very rough, with a moderate vibration (of course this had to happen while we were over Lake Erie). I pulled carb heat and advanced the throttle back to 2400 rpm which smoothed it out. I kept us at 2400 until I was sure we could glide to the field, then pulled back to 1900 again, and this time everything was fine.
My Cherokee 140 POH doesn’t call for regular carb heat, saying something like “when necessary”...I think I discovered when “necessary” is...One thing I was expecting with a carb ice encounter that didn’t happen: I’ve heard of engine vibrations getting temporarily worse when carb heat is first applied (as the ice melts), but I only noticed things settling down after carb heat. Or, could it have been something else? I don’t know..I do know we had no problems on the hour flight home.
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Good job Tawood. Sounds like you were correct. Good plan to keep the power up until you made land fall or the destination airport. If it was a lot of ice you could experience it running rough after application of carb heat. Maybe it wasn't enough and you caught it early. Really hard to say.
 
Your good training seems to have paid off.
 
Unit74 said:
What if you don't suspect it, but want to keep it from happening though. That was my position with partial carb heat. Raise the ambient air temp in the induction to keep it from happening. If you suspect it, full on till it clears up. Then a few min more for good measure!
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This works well if you have a Carb Temp gage. If not, you may raise the throat to 33°or 34°, then the ice will just form further down in the throat . . . where Full carb heat may not melt it . . . . .
 
Nice work, tawood. You might consider revising your checklist based on this experience.

Not sure how applicable to your Cherokee, but some aircraft actually run a little smoother in some conditions, with a little carb heat, once you’ve adjusted the mixture. The O-470 182’s tend to have fairly poor fuel/air distribution in the intake manifold. A touch of carb heat sometimes helps improve distribution, resulting in smoother operation.
 
This is a good learning experience, and a good and sensible reaction on your part. I suspect many of us have had the same lesson in humid conditions. It's a non-event if you respond appropriately. Like your plane, the Grumman POH suggests applying carb heat "if needed." It rarely is needed, but on occasion...

Unfortunately a few years ago, a recently certificated pilot in our area likely didn't respond as you did and wound up crashing a perfectly good aircraft when the engine subsequently quit. Carb icing is strongly suspected to be the precipitating cause based on prevailing weather conditions and no demonstrable mechanical cause. I've had icing in not-quite-full-throttle cruise in very humid conditions, and appear during long descents in visible moisture or excessively humid conditions in summer and winter. When the engine stumbles for no obvious reason, carb heat should be one of the first things you check (before going through the rest of your engine failing checklist.)
 
tawood said:
Kristine and I were filming for our blog at the time, so I’m gonna have to review the video again, but my recollection was I reduced power, the engine became very rough, and after maybe 5 seconds of rough running, I pulled carb heat. Over the next five seconds, the engine gradually smoothed out, and then I added power. Oh, and during that 10 seconds, I did a lot of swearing, lol, while Kristine said, “What? What? What?” She said later she didn’t notice anything, which I was surprised because I couldn’t imagine how it could be missed, as it vibrated pretty bad for 5 or so seconds.
Click to expand...

OK, *NOW* it sounds like carb ice. ;) You should post the video here!

BTW, you'd be surprised what a non-pilot, or even a pilot who doesn't know the particular airplane, doesn't feel/hear/see that you do.
 
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