Carb Heat, Cherokee 140 POH

Andy Greever

Andy Greever

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I was looking at the original POH for my Cherokee a few days ago and noticed someone had underlined a sentence, and I quote, "Carburetor heat should not be applied unless there is an indication of carbureter icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat on is likely to cause detonation." end quote.

So if I forget to use carb heat during my checkride could I point out this little tidbit to the DPE? I've heard the POH is a "Legal Document" is that true?

Should I test the carb heat before entering the pattern and don't use it if there is no sign of ice? (rpm drop during use indicates no ice right?)
 
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You do not need to have carb heat on for that airplane when going to low RPMs unless there is an indication of carb ice. Which of course would be a reduction of RPM while at cruise, roughness, etc. In the pattern flipping it on and then off quickly probably would not tell you if you had carb ice as there would not be enough time to melt stuff in there, you would need to leave it on for a bit longer and then remember to turn it off again.

The operative word here are "Carburetor heat should not be applied". Should implies an optionality, if the words were shall not then you never put on the carb heat. But with 'should not' you can have it on or off, just add turning it off in your flow for the go around. But I would just leave it off for those days when carb ice is highly unlikely.
 
Thanks for the quick reply.

I promise not to start another Headset thread! :D
 
This is one thing that took some getting used to when I transitioned from C-152/172s to Cherokees. I was taught to always use carb heat in the Cessnas and not to touch it in the Cherokees unless I had a suspicion that there was something afoul. Essentially, as long as the engine isn't misbehaving in some way then I don't even think about it. Though it would be one of the first things I would reach for if I heard a hiccup.
 
A few days ago (Story time) I was flying my Warrior and the engine started getting rough. Sorta like one of the cylinders was missing. RPMs were good so the first thing I did was check left or right only mag positions but there was no change. So next up was the carb heat, again no change except for the RPM drop. I then added a little fuel via richening the mixture and sure enough it smoothed out. I had over leaned.
 
I guess the question is how good of a weather forecaster you are.

I remember my early days in ground school, way back before there were hardly any fuel-injected engines around, the instructor drilling it into us that carb ice could form *even on a sunny, clear day!*

So, you gotta know your atmospheric conditions. Is the temp/dew point spread close? Is the relative humidity high? Then, I'd probably kick in some carb heat on final for safety's sake, just to make sure the thing didn't ice up on me at the most inopportune time.
 
WIth the Pipers and Lycomings, carb ice is a rarity. In almost 400 hours of Piper/Lycoming time I've had carb ice just once, and I'm not even sure it was carb ice. Carb ice can form in high humidities, but in the Piper/Lycoming set up I NEVER use it unless I have the RPM drop. Sorry PHX, gonna have to overrule you on this one in regards to the Cherokee 140, I'd rather have the power.
 
EdFred said:
WIth the Pipers and Lycomings, carb ice is a rarity. In almost 400 hours of Piper/Lycoming time I've had carb ice just once, and I'm not even sure it was carb ice. Carb ice can form in high humidities, but in the Piper/Lycoming set up I NEVER use it unless I have the RPM drop. Sorry PHX, gonna have to overrule you on this one in regards to the Cherokee 140, I'd rather have the power.
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As a student in a PA-28-181, I was coming in for a landing with my CFI. On very short final the engine very suddenly developed a roughness. My CFI and I both reached for the carb heat. We landed uneventfully and taxi-ed to the ramp. Don't know if it was carb ice or not, but hey, that is what the heat control is for! As others have said, make Carb Heat Off part of your go-around flow.

That's the only time I have suspected Carb Ice in a Piper.

Here is a graph of when the atmosphere is conducive to carb ice. Note that this doesn't predict when you will have ice, as it is not dependent on a specific engine. Brand P forms ice a lot less frequently than Brand C.

-Skip
 

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Skip Miller said:
As a student in a PA-28-181, I was coming in for a landing with my CFI. On very short final the engine very suddenly developed a roughness. My CFI and I both reached for the carb heat. We landed uneventfully and taxi-ed to the ramp. Don't know if it was carb ice or not, but hey, that is what the heat control is for! As others have said, make Carb Heat Off part of your go-around flow.

That's the only time I have suspected Carb Ice in a Piper.

Here is a graph of when the atmosphere is conducive to carb ice. Note that this doesn't predict when you will have ice, as it is not dependent on a specific engine. Brand P forms ice a lot less frequently than Brand C.

-Skip
Click to expand...

Yep. Not saying it never happens, just that it has never happened to me. Looking at that graph, it seems I fly in that yellow range most of the time. Of course when I did the training in the 152, we did run into carb ice more than once, and I only have a fraction of the hours in that as I do Cherokees. And with my Cherokee, I've flown it from -5F to 115F, and in all ranges of humidity as well - which is why I never use carb heat until I have that roughness/RPM drop - which I have only had once, but I'm not sure it was even carb ice.
 
My instructor has had two or three carb ice incidents over a 15 year career in Piper single-engines.

Of course, that's LOTS of hours. I've never had one in my 180 hours in Warriors, Archers, and a Cherokee 180. I only turn it on descending in actual IMC or when the engine gets rough (which hasn't happened yet).
 
I've not flown a Piper of any model. Where is the carburetor mounted on the engine? In relation to the cylinders, be they four or six?
 
Skip Miller said:
As a student in a PA-28-181, I was coming in for a landing with my CFI. On very short final the engine very suddenly developed a roughness. My CFI and I both reached for the carb heat. We landed uneventfully and taxi-ed to the ramp. Don't know if it was carb ice or not, but hey, that is what the heat control is for! As others have said, make Carb Heat Off part of your go-around flow.

That's the only time I have suspected Carb Ice in a Piper.

Here is a graph of when the atmosphere is conducive to carb ice. Note that this doesn't predict when you will have ice, as it is not dependent on a specific engine. Brand P forms ice a lot less frequently than Brand C.

-Skip
Click to expand...


Good graph. I like it. Do you know its source?

In any case, for those who want the extra power on landing, that's why you turn off carb heat on a go-around.

But, if it's a normal landing, you're probably going to be working the throttle out to idle, so you don't really need a lot of power. So, if/when you need the extra power, such as on a go-around, you simply turn off carb heat and advance throttle.

I have most of Lycoming's training manuals and bulletins laying around. I'll try to find some time and look up what they say about carb ice. I do recall seeing something in their literature showing a picture of what carb ice really looks like, and it wasn't pretty.
 
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PHXAvi8tor said:
Good graph. I like it. Do you know its source?
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Specifically, no. I found it with Google. It appeared at the time (if memory serves) that it came from the Canadian equivalent of the FAA in one of its advisory publications. But again, that is from memory.

-Skip
 
KennyFlys said:
I've not flown a Piper of any model. Where is the carburetor mounted on the engine? In relation to the cylinders, be they four or six?
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The carb is on top of the engine in the PA28 line.

Also, as to the original question, follow the POH. It says no carb heat unless you have symptoms of carb ice, then no carb heat unless you have symptoms of carb ice. If a DE has a problem with you following the POH, there's a bigger problem than whether you should turn the carb heat on every landing or not.
 
My CFI trained me to apply carb heat in the Warrior only when temp/dewpoint within 6 deg, and only during descent. Once in the pattern, turn it off and leave it off unless engine indications call for it.

I'll have to check my own POH for the -161 and review what it specifically states about carb heat during descents.
 
msmspilot said:
The carb is on top of the engine in the PA28 line.
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Yeah but the engine is mounted with the 'top' facing down. So the carb is on the bottom of the installed engine. Not sure I understand your point though.

Not sure in the cessnas but in the pipers exhaust goes very near the carb so the carb is warmed by that heat and that could be the difference as to why pipers seem to be less prone to carb ice.
 
I've been told it's due to the routing of the oil lines that keeps the carb warm enough to prevent most ice in a Piper.
 
PHXAvi8tor said:
So, you gotta know your atmospheric conditions. Is the temp/dew point spread close? Is the relative humidity high? Then, I'd probably kick in some carb heat on final for safety's sake, just to make sure the thing didn't ice up on me at the most inopportune time.
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I think turning on carb heat "for safety's sake" alone is inappropriate. Using carb heat when not needed can take away power you might need (especially if you have to go around and forget to turn it off), as well as letting dirt and grit into the engine since you've bypassed the air filter (always a consideration near the ground) -- that may not be a short-term consideration, but it affects engine longevity.

As an instructor, I believe it is important to teach procedures meaningfully, not on the basis of "safety's sake" with no identifiable gain or reason for doing it. That's how folks wind up running planes off the end of the runway -- adding 5 or 10 knots "for mom and the kids" on final approach (i.e., "for safety's sake"). Therefore, I teach folks to use carb heat as suggested by the POH. For a 1965 Cessna 150, that means any time you're below the green arc. For a 1979 Grumman Tiger, that means when you experience symptoms of carb ice. For other planes, well, read the book.
 
So it's been a while since I flew a 152, but doesn't its tach have a specially colored arc in which you're supposed to use carb heat? The Piper tach doesn't have this arc.

In over 500 hours in a PA28-180, I have never had a carb ice incident.
 
I just called my mechanic to verify that carb ice is indeed what I had on initial climb-out yesterday. Temps and dewpoints were within a few dgrees and the temp was 34 degrees F on the ground.

What was wierd to me is I got the severe roughness as I lowered the nose and reduced power after the full power climb. It was only with reduced power that the MP dropped. It seemed fairly normal up until then.

I didn't have the sense to apply carb heat. I just put the power back in. As Rod Machado says when you do something and something bad happens you undo the last thing.

I figger that the engine was still cold but it heated up and did its own version of applying carb heat in a few minutes.

In ten years of flying my bird that is the very first time I can say I had carb ice. I had no idea it would have that symptom. Lesson learned.

Time for some emergency sim refresher on some dual for me.
 
i posted on a thread that i read a few months back on this same topic..all i fly is warriors or cherokees and i posted that i always turned on the carb heat for safety pre-caution even tho the POH didnt say to do so...i thought i was doing a good thing...Someone convinced me that even if you have carb heat on for a pre-caution that you can still get carb icing..and then what are you gonna do, since u already have the carb heat on?? :( time to land....
so now i do exactly what the POH says...casue in the end..im sure the people who built and designed the plane know a heck of alot more about it then i do...and i would trust that they arent gonna give you advice that could kill you...

Ant
 
I think Cap'n Ron's advice earlier in this thread is right on: Do what the POH says to do, but you better be sure that you've ensured there aren't some other overriding reasons to deviate!

(Example: In another thread on soft-field takeoffs, many would agree to deviate from the POH and leave the gear down a bit longer than the POH recommends, for safety reasons.)

My earliest training was in a C-152, and in that particular configuration, the carb heat went on regardless of atmospheric conditions on final approach.

And, it wasn't just "for safety's sake." It was because that was what the A&P guys, the flight school, the manufacturer, and everyone else determined was the safest course of action.

NEVER, ever, do something mindlessly just "for safety's sake." Ever. if you choose to deviate from the POH, you better be able to back up your procedures based on the POH, ACs, ADs, and all other known data.

In the absence of some of that known data, then you have to use common sense and your best pilot judgment -- and the POH, as amended by ADs and other regulatory updates to it.
 
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Woody said:
So if I forget to use carb heat during my checkride could I point out this little tidbit to the DPE? I've heard the POH is a "Legal Document" is that true?
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FORGET carb heat? Yes, you should forget carb heat in the Cherokee. Is your CFI telling you that you have to use carb heat in the Piper? If so, you might want to find a new CFI. Use the POH procedures.

Should I test the carb heat before entering the pattern and don't use it if there is no sign of ice?
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Test it during your runup. You should get an RPM drop, but no roughness. Be prepared to answer the question "So, why does carb heat cause an RPM drop?"

If you turn carb heat on in the air and get a *sustained, consistent* drop you probably don't have ice. If you get a big drop and it's rough for a couple seconds and then comes back up, you had ice.
 
Unless your DPE has never been in a Cherokee before (ie, not bloody likely!) they already know this.

If they ask, just tell it like it is. They'll probably be astounded that you actually read the POH. ;-)

And yes, use of carb heat does reduce your available power, which is the LAST thing you want in a marginally powered airplane when trying to do a go-around. :hairraise:

Woody said:
I was looking at the original POH for my Cherokee a few days ago and noticed someone had underlined a sentence, and I quote, "Carburetor heat should not be applied unless there is an indication of carbureter icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat on is likely to cause detonation." end quote.

So if I forget to use carb heat during my checkride could I point out this little tidbit to the DPE? I've heard the POH is a "Legal Document" is that true?

Should I test the carb heat before entering the pattern and don't use it if there is no sign of ice? (rpm drop during use indicates no ice right?)
Click to expand...
 
flyingcheesehead said:
FORGET carb heat? Yes, you should forget carb heat in the Cherokee. Is your CFI telling you that you have to use carb heat in the Piper? If so, you might want to find a new CFI. Use the POH procedures.



Test it during your runup. You should get an RPM drop, but no roughness. Be prepared to answer the question "So, why does carb heat cause an RPM drop?"

If you turn carb heat on in the air and get a *sustained, consistent* drop you probably don't have ice. If you get a big drop and it's rough for a couple seconds and then comes back up, you had ice.
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No, my CFI's have been teaching me to touch it during the pre-landing to show the examiner that I gave it thought before landing.

The reason you get a power drop, is because hot air is less dense than cold air, so you have less oxygen available for combustion, therefore less power. (close enough to pass?)
 
Woody said:
No, my CFI's have been teaching me to touch it during the pre-landing to show the examiner that I gave it thought before landing.
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Ah, OK. You could also just say "no carb heat necessary..."

The reason you get a power drop, is because hot air is less dense than cold air, so you have less oxygen available for combustion, therefore less power. (close enough to pass?)
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Sounds passable to me.
 
Apparently DPE's around here have been busting people on their checkrides, for not using carb heat. (apparently folks in Arizona are lazy about using carb heat, and thay're checking for it)

I figure I've got that base covered now! Gotta Love Cherokees! :yes:

Thanks for the help, to all who posted.
 
Thanks to Google I came across this very old thread and wanted to add to it. We recently had a PA28 in our club suffer carb icing in the circuit (pattern) and was not recoverable due to the low altitude. Fortunately instructor and student walked away with relatively light injuries.

Our club trains only on PA28's and is strict about the use of carb heat on descent, switched off before touchdown or a go-around. Our airfield is at 150 AMSL so even with carb heat on the aircraft will always climb with 2 on board, although not best climb. We are also trained to run carb heat for 30s every 15min when running the FREDA check. On the topic of training best practice which covers aircraft not being flown, we also call "undercarriage" during the downwind BUMFICH checks despite have fixed gear. On day it might save someone's life in an Arrow and costs nothing.

I was surprised that apparent concensus of the forum was not to use carb heat.

I have experienced carb icing in a PA28 several times, recently during an emergency descent, despite having the carb icing on. Our 1969 -140 POH makes no mention of the use of carb heat, except under "Balked Landing" which states after the normal procedure of full throttle, allowig the sped to increase to 73mph and raising the flaps, "Carburetor heat off, unless icing exists". The implication is that the carb heat would have been applied during the descent. That is certainly what I do.

While there is a risk that someone would not switch off carb heat and climb slowly until they do, the risk and consequence of carb icing at low altitude seems considerably greater.

Perhaps it is because the UK is probably amost always at high humidity, but I was surprised to be asked by the instructor not to use carb heat when flying a PA28 in the USA. It feels like a cheap safety margin to me, as there are many unexplained power loss accidents explained as probably carb icing.

I'd be very interested in hearing if thinking has changed in this area since the topic was last discussed.

Safe flying

Christopher
 
Those who have never had carb ice are living a charmed life.
I have encountered severe icing at temperatures as low as 10F while at 10,000 feet directly over Detroit Metro. Yes, this was in your supposed no-ice Piper. It almost became an emergency before the ice began to clear.
When you apply carb heat you must also lean aggressively. You will recover most of the RPM drop. And you will make more heat ensuring the ice clears. This is automatic for me when entering the pattern. The mixture is simply pulled back about 2/3 of the way to cutoff as soon as heat is applied. The engine remains warm and there is no big rpm drop.
 
crackle said:
I'd be very interested in hearing if thinking has changed in this area since the topic was last discussed.

Safe flying

Christopher
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Welcome to POA! :cheers:Great first post, I'll be watching from the sidelines in regard to the Cherokee...
 
Welcome, Christopher!

crackle said:
Our 1969 -140 POH makes no mention of the use of carb heat, except under "Balked Landing" which states after the normal procedure of full throttle, allowig the sped to increase to 73mph and raising the flaps, "Carburetor heat off, unless icing exists". The implication is that the carb heat would have been applied during the descent. That is certainly what I do.
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The 1968 Owners Manual (screenshot below) does have the "should not be applied unless there is an indication" language in the "Normal Procedures -- Approach and Landing" section. So does the more detailed POH for the 1977 PA-28-140, the last year of production. Years ago I instructed in 1969 140s, and I'm sure that was the same.

Like others above, I have experienced carb ice in Cherokees, though nowhere near as often as in Cessnas with the same engines.

That said, I'm somewhat ambivalent about routinely using carb heat in Cherokee 140s without an indication of carb ice. If atmospheric conditions are ripe for it, it goes on. If I don't use it on a particular approach, it's in the back of my mind and I'm watching for indications of ice.

It's worth keeping in mind that with carb heat on the engine is getting unfiltered air, so one must remember to shut the heat off as soon as possible after landing. And I would try to avoid using the carb heat in dusty conditions.
 

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I did my initial training in Cherokees and was always told only use the heat when icing suspected. Not potential conditions, suspected to exist.

Transitioning to 172's I had numerous hand slaps for pulling power without turning on the heat first.

Then, I did some IFR training in a Cherokee with a "newer" instructor who was in the carb heat always camp. Since she worked for my primary instructor I had the best chance of clarification.

Citing the POH as the most authoritative guidance.... Cherokee Carb Heat off unless suspect ice exists, Cessna carb heat ON during all low power descent.
 
I always taught and practiced to turn carb heat off on short final, max power and it's filtered air for when you get low where you'll have dirt.
 
When I was taking my lessons in the 140.. it was carb heat on abeam the numbers then off on final.. I definitely forgot to turn it off a time or two.. Since then while flying I only have experienced carb icing (engine roughness) once.. I recognized it immediately and applied carb heat and it was a non-issue at that moment... I follow the POH and use my best judgement to keep me safe...
 
Ancient thread is ancient :D

I owned and flew a Cherokee 140 for 10 years and never encountered carb ice with it, but that doesn't mean it's immune from carb ice. I have encountered carb ice in a Lyc equipped C172 and also in my Lyc equipped RV6 and it definitely get your attention quickly!

I do have to disagree with the mention that detonation is a worry with carb heat applied in a low compression Cherokee 140 this day and age with 100LL fuel. Maybe back in the olden days with 80 octane avgas, but with 100 octane fuel you'll be hard pressed to get 7:1 compression O-320 to suffer detonation.
 
In our Maules we teach carb heat anytime the power is below 2000 RPM. The carb is bolted to the firewall with a good size air gap between it and anything remotely warm.

I get carb icing at least one or twice a month.
 
Got carb. ice in a 172 on a missed approach in actual.
Never had an issue in any Piper, as of this date.
 
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