Carb Ice Frequency for Mooneys

[pirate]

Since 1995 I had cab  ice once returning from Florida during February.  DPA ILS ran into some lake effect snow poping in and out of cloud. I noticed a rough run, pulled carb heat and heard several backfires then cleared up. I had a carb temp installed before flying in those conditions again. Never had carb ice during VFR flight, but ya never know. 

 

[G Miller]

Hear in the Pacific Northwest, the icing capitol of the world, I started experiencing carb ice as soon as I purchased my M20C. I installed a carb temperature probe that drives my EI engine monitor. I have found that once at altitude, setting the carb temp to 50 deg F, and leaning the mixture appropriately, makes for a smoother running engine and the EGTs are more balanced. 

[MBDiagMan]

I thought I had responded to this thread a long time ago, but it must have been a different thread on the same subject.

Due to the introduction of unfiltered air, I really don’t like using carb heat if it is unnecessary.  My Cessna has a carb temp gauge.  I flew it many hours before buying my C.  I never used carb heat unless the carb temp was in the yellow or red range.  It worked out beautifully and I never had an issue.  Fortunately when I bought my C, it had the very same carb temp gauge arrangement so I followed the same procedure.

I highly recommend having a carb temp gauge in a carbureted aircraft and develop the habit of observing the gauge when beginning descent and on downwind and using carb heat if necessary, but if not necessary don’t use it.

That said, for those of you in a more damp and cool climate, it might be better to just always use it, but you wouldn’t know unless you flew with a carb temp gauge for a while.

As an important side note, unfiltered air at low altitudes where dust exists will wear the top piston rings rapidly.

[triple8s]

Just want to say you can easily get carb ice when there is no visible moisture. If you are flying a carb engine use carb heat as instructed in the poh. I have seen many central heat and air units froze up and they weren't flying through visible moisture. Seriously follow the poh and I had a carb temp gauge so I could tell when the carb temp would get below freezing. You be surprised how cold a carb will get when throttle is anything but wide open. Once it gets iced up and quits you have zero heat for the carb heat function.

[81X]

I’ve only had carb ice once in my Cherokee 180 (similar engine) and it was at reduced power on approach in the soup flying into Lancaster PA in early fall. OATs were about 50 but it sure got my attention and took a minute to clear up!  

Agree with most that the cooling flow of the Lycoming 360’s generally keeps the carb nice and warm. Continental 360’s in a 172?  Not so much. 

[Hank]

9 minutes ago, 81X said:

I’ve only had carb ice once in my Cherokee 180 (similar engine) and it was at reduced power on approach in the soup flying into Lancaster PA in early fall. OATs were about 50 but it sure got my attention and took a minute to clear up!  

Agree with most that the cooling flow of the Lycoming 360’s generally keeps the carb nice and warm. Continental 360’s in a 172?  Not so much. 

The 172 I got my license in (Lycoming O-320) was totalled a couple of years later in a carb ice incident--engine started running rough so the pilot tried to land with a tailwind, was fast and tried to go around. He made it about 150 yards past the end of the runway. He and his wife were walking out of the trees, bleeding, by the time people drove over from the FBO.

I've never had carb ice, nor pulled Carb Heat because I thought I did, in over 11 years of ownership. But I have used it twice prophylacticly in Instrument training during a Midwest winter. Have I said lately how much I appreciate my Carb Temp gage?  

[Bob_Belville]

I guess it would be seen as unseemly to mention fuel injection? 

[Hank]

42 minutes ago, Bob_Belville said:

I guess it would be seen as unseemly to mention fuel injection? 

No more than me taunting people who have hot start issues with how simple and quick it is to hot start my O-360 . . . . .  

[Mooney-Mark]

I use carb heat, with mixture leaned, up until short final then full forward with mixture and prop on final GUMP check before landing. Pull carb heat occasionally during long descents with power back. Have never had carb ice.

[gsxrpilot]

My M20C experience was limited to only 400 hours over a couple of years. But there was lots of actual IMC during that time. I never once pulled the carb heat other than during run-up to verify it's function.

[Boilermonkey]

My M20C experience was limited to only 400 hours over a couple of years. But there was lots of actual IMC during that time. I never once pulled the carb heat other than during run-up to verify it's function.

Your lucky then...had three times last year. What are the odds.

Sent from my SM-G960U using Tapatalk

[Hank]

5 hours ago, Mooney-Mark said:

I use carb heat, with mixture leaned, up until short final then full forward with mixture and prop on final GUMP check before landing. Pull carb heat occasionally during long descents with power back. Have never had carb ice.

I've had plenty of long descents (beginning 50nm or more from destination), but what does "long descent with power back" mean? As I descend and MP rises, I pull it back to whatever my cruise setting was, then richen to regain my cruise EGT. I save power reduction for slowing down before pattern entry.

[midlifeflyer]

58 minutes ago, Hank said:

I've had plenty of long descents (beginning 50nm or more from destination), but what does "long descent with power back" mean? As I descend and MP rises, I pull it back to whatever my cruise setting was, then richen to regain my cruise EGT. I save power reduction for slowing down before pattern entry.

It means what it sounds like - a long descent with the power pulled back to settings which would be conducive to carb ice formation. You are doing engine management to keep your power at cruise settings during your descent. Others might use a different procedure where they reduce power to lower levels to increase descent rate closer in while not building airspeed. And in the IFR world of high moisture content and not being able to always choose our TOD, it can be an issue.

[steingar]

Only carb ice I ever got was flying through really thin wispy clouds just above freezing.  I was on approach to land at my nearest (had the runway made, too) when the carb heat brought the engine back on line.  Never saw a whiff it flying for ten years in my Cherokee and three (well, three of ownership. With all the crap done to my airplane it seems like I've spent 10 minutes flying it) of my Mooney. 

[WilliamR]

4 hours ago, steingar said:

Only carb ice I ever got was flying through really thin wispy clouds just above freezing.  I was on approach to land at my nearest (had the runway made, too) when the carb heat brought the engine back on line.  Never saw a whiff it flying for ten years in my Cherokee and three (well, three of ownership. With all the crap done to my airplane it seems like I've spent 10 minutes flying it) of my Mooney. 

Funny, your Mooney is the one I had a carb-ice event at cruise at 7,000'.

[steingar]

19 hours ago, WilliamR said:

Funny, your Mooney is the one I had a carb-ice event at cruise at 7,000'.

Ouch!  I'll be on the lookout of that.  Admittedly, I've been sidelined for most of two winters in the three years of my ownership, but I'm not IFR< so I don't go through visible moisture that much.  The one time was really wispy clouds, I still had tons of vis.

Oh, and I forgot to thank you for taking such good care of my Mooney.  She obviously flourished under you stewardship.

Edited December 14, 2018 by steingar

[jaylw314]

49 minutes ago, steingar said:

Ouch!  I'll be on the lookout of that.  Admittedly, I've been sidelined for most of two winters in the three years of my ownership, but I'm not IFR< so I don't go through visible moisture that much.  The one time was really wispy clouds, I still had tons of vis.

I might be beating a dead horse, but carb ice does not require visible moisture, just humidity

[N201MKTurbo]

Back in my high school years I was into Corvairs. I had a 140 horse engine. This engine originally came with 4 one barrel carbs. I put on a custom intake that looked like a header and had a Holly 2 barrel on a collector over the center of the engine. This put the carb a long way from any heat source. Even on a 100 degree day if it was humid enough you could open the engine compartment and find a block of ice formed just under the carb on the manifold.

[steingar]

15 hours ago, jaylw314 said:

I might be beating a dead horse, but carb ice does not require visible moisture, just humidity

You are of course correct, but where I live there isn't that much humidity on days cold enough to get carb ice.  Only time I've had it there was visible moisture.  That said, once I start doing the IFR thing, I suspect I'll be using it plenty.

[midlifeflyer]

52 minutes ago, steingar said:

You are of course correct, but where I live there isn't that much humidity on days cold enough to get carb ice.  Only time I've had it there was visible moisture.  That said, once I start doing the IFR thing, I suspect I'll be using it plenty.

Just a thought on using carb ice as a preventive vs using when you need it. 

Back in 1990, the NTSB made a recommendation to both the FAA and GAMA that carb ice should always be used as a preventive. They gave a number of reasons for it. It makes an interesting read, although it went nowhere.

I came across it during research after my own carb ice event - a 250 HP Comanche at full cruise power in the clouds over the Rockies with the air temperature in the 70s. In addition to the NTSB report, I queried the ASRS (NASA Report) database and found a number of reports similar to mine and which echoed part of the NTSB findings - people who didn't detect carb ice soon enough, in part because, not using it regularly led to an "out of sight-out of mind condition" - no automatic mental association between low power and putting on carb heat. 

In my case, I did all sorts of trouble shooting and things I did automatically in the Comanche - boost pump on, went to best glide immediately, switched tanks, played with the mixture. I did apply carb heat - eventually - but too late to have effect when it was needed most.  After breaking out (high ceilings, fortunately) within easy distance to an airport, I even unconsciously lowered the gear at the point in the approach where I always do.

You name it, I did it. Except one essential  - the one I did not do regularly.

I can still see reasons for not using it as a preventive in aircraft where the POH calls for "as required" (a definitive Cirrus CAPS-style "consider" in the checklist/flow might be decent alternative) But in an aircraft where the manual says to use it as a preventive, I don't see a very good reasons to not get into the SOP habit.

[steingar]

Thanks for the thoughts.  Yeah, I do plan on using it fairly proactively once I start penetrating clouds.  A really really really good friend of mine was lowered into a cloud bank by his CFI, the reasoning being that if he encountered IFR conditions he wouldn't panic and be able to fly his way back out.  Carb heat came on before they hit he cloud.

[Hank]

Just be aware that carb ice can form outside of clouds and in temps well into shirt-sleeve / no-heat-required temperatures. That's how the sturdy Cessna that I had used as a student met its end. In Ohio, 45 Mooney minutes from you, @steingar. But it is less of a problem for our Mooneys.

Edited December 14, 2018 by Hank

[jaylw314]

2 hours ago, midlifeflyer said:

Just a thought on using carb ice as a preventive vs using when you need it. 

Back in 1990, the NTSB made a recommendation to both the FAA and GAMA that carb ice should always be used as a preventive. They gave a number of reasons for it. It makes an interesting read, although it went nowhere.

I came across it during research after my own carb ice event - a 250 HP Comanche at full cruise power in the clouds over the Rockies with the air temperature in the 70s. In addition to the NTSB report, I queried the ASRS (NASA Report) database and found a number of reports similar to mine and which echoed part of the NTSB findings - people who didn't detect carb ice soon enough, in part because, not using it regularly led to an "out of sight-out of mind condition" - no automatic mental association between low power and putting on carb heat. 

In my case, I did all sorts of trouble shooting and things I did automatically in the Comanche - boost pump on, went to best glide immediately, switched tanks, played with the mixture. I did apply carb heat - eventually - but too late to have effect when it was needed most.  After breaking out (high ceilings, fortunately) within easy distance to an airport, I even unconsciously lowered the gear at the point in the approach where I always do.

You name it, I did it. Except one essential  - the one I did not do regularly.

I can still see reasons for not using it as a preventive in aircraft where the POH calls for "as required" (a definitive Cirrus CAPS-style "consider" in the checklist/flow might be decent alternative) But in an aircraft where the manual says to use it as a preventive, I don't see a very good reasons to not get into the SOP habit.

Is there really any negative to using carb heat all the time (in cruise flight, anyway)?   I don't know by how much it would decrease your speed at full throttle, is it that significant in the O-360?  Arguments about unfiltered air seem disingenuous in a plane that has a ram air intake, and if you left it on all the time, you wouldn't need to change the mixture.

[midlifeflyer]

2 hours ago, jaylw314 said:

Is there really any negative to using carb heat all the time (in cruise flight, anyway)?   I don't know by how much it would decrease your speed at full throttle, is it that significant in the O-360?  Arguments about unfiltered air seem disingenuous in a plane that has a ram air intake, and if you left it on all the time, you wouldn't need to change the mixture.

I'm no mechanic but with heated air entering the carburetor instead of the nice cool air from outside, I would expect the cooling effects of air intake to have to battle the heating effects. I wouldn't be surprised to see an increase in both oil temperatures and CHT.  I guess that's what the FAA's Aviation Maintenance Technician Handbook means when it says, 

Improper or careless use of carburetor heat can be just as dangerous as the most advanced stage of induction system ice. Increasing the temperature of the air causes it to expand and decrease in density. This action reduces the weight of the charge delivered to the cylinder and causes a noticeable loss in power because of decreased volumetric efficiency. In addition, high intake air temperature may cause detonation and engine failure, especially during takeoff and high power operation. Therefore, during all phases of engine operation, the carburetor temperature must afford the greatest protection against icing and detonation.

There's also a discussion of how induction of snow or ice crystals can cause damage in much the same way as the ulfiltered air on the ground.

In terms of power loss, the Pilots Handbook of Aeronautical knowledge indicates a loss of up to 15%.Makes sense to me. In my situation I was at about 12,000 MSL with temps around 70F. so over 15,000 ft D-alt.  Using the 3% loss of power/ 1,000' rule of thumb, my 250 HP engine was already down to about 160 HP. I'm not sure how knocking off another 15% would be helpful.

Edited December 14, 2018 by midlifeflyer

[jaylw314]

10 minutes ago, midlifeflyer said:

I'm no mechanic but with heated air entering the carburetor instead of the nice cool air from outside, I would expect the cooling effects of air intake to have to battle the heating effects. I wouldn't be surprised to see an increase in both oil temperatures and CHT.  I guess that's what the FAA's Aviation Maintenance Technician Handbook means when it says, 

Improper or careless use of carburetor heat can be just as dangerous as the most advanced stage of induction system ice. Increasing the temperature of the air causes it to expand and decrease in density. This action reduces the weight of the charge delivered to the cylinder and causes a noticeable loss in power because of decreased volumetric efficiency. In addition, high intake air temperature may cause detonation and engine failure, especially during takeoff and high power operation. Therefore, during all phases of engine operation, the carburetor temperature must afford the greatest protection against icing and detonation.

There's also a discussion of how induction of snow or ice crystals can cause damage in much the same way as the ulfiltered air on the ground.

In terms of power loss, the Pilots Handbook of Aeronautical knowledge indicates a loss of up to 15%.Makes sense to me. In my situation I was at about 12,000 MSL with temps around 70F. so over 15,000 ft D-alt.  Using the 3% loss of power/ 1,000' rule of thumb, my 250 HP engine was already down to about 160 HP. I'm not sure how knocking off another 15% would be helpful.

I had forgotten the 15% thing, thanks.  Do people with carb temperature sensors routinely run partial carb heat if the carburetor temp is below freezing?