Cherokees and Carb Heat

rframe

rframe

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I've got a primary student with a Cherokee 180 now and I'm really debating about changing the checklist and having him turn on carb heat during each landing. I know this has been discussed some before but just want to get some more feedback on what you actually teach?

I've read the NTSB recommendation that Cherokees are flown with carb heat during landings (like Cessna), but understand Piper and the FAA didn't want to change it.

Here's my logic.
  1. There's no real cost doing so - ok there's potential I'll break out but I dont believe they are valid
    1. Possible ingestion of bugs/dirt but very unlikely in flight and thousands of other airplanes are flown this way with the same risk and I've not heard of it actually being a problem
    2. Piper says with carb heat on and applying power during a go-around you're robbed of horsepower...well duh, that's why you turn it off as part of the go-around - not a hard problem to solve
    3. Piper says because of the leaning you could cause detonation with carb heat and full power... I find that one hard to believe unless you were already quite lean and hot (not likely since you are descending with low power) but we've already solved it by turning off carb heat during the go-around anyway.
  2. If carb ice does develop (I know its less likely on this airframe but does happen) it must first be detected, recognized, and heat applied in time for the residual heat to have any effect all while possibly low and slow during a landing approach or go-around situation... seems a lot more effective to use as an anti-icing system than hoping to melt a clogged up mess right when I need power
  3. More consistent flow and memory aid that will transfer to other airplanes
What do you guys do? Heat abeam the numbers or only as an emergency procedure?
Am I missing any considerations?
 
At school we had this problem with the new warriors and developing a procedure. Piper said that their carb heat was so much hotter than the Beechcrafts we had that it really only needed to be used with the detection of carb ice and not preventative. They said that damage could occur with prolonged use and advised us if it was better to keep it off. The chief pilot also agreed with piper because of his previous experience and some metal warping issues he had.
 
I think rframe knows I agree with him and his rationale. Cessnaflyer, you seem to have had some practical exposure to the issue, so let me ask: as far as you know, is the concern (including those warping issues) based on "prolonged" use of carb head below 2000 RPM (where we typically use it in other aircraft)?
 
MidlifeFlyer said:
I think rframe knows I agree with him and his rationale. Cessnaflyer, you seem to have had some practical exposure to the issue, so let me ask: as far as you know, is the concern (including those warping issues) based on "prolonged" use of carb head below 2000 RPM (where we typically use it in other aircraft)?
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I agree with Russ as well, I was giving him the advise we received from Piper when we did a partial fleet replacement so he didn't have to go the extra step and ask Piper.

From what I can remember since it was 5 years ago since I worked at the college, it was caused by using heat like it was a Cessna. What we finally came down as an acceptable procedure was to put the heat on during the base leg. There was no damage to the Pipers and the Sports and Sundowners didn't have any icing troubles.
 
Listen to piper. They built the thing and they know what they are talking about. Except as to build a habit for Cessna(continental really) there's just no need. At my flight school we did not use it because of the wear and tear on the cable. You'll go through 10,000 cables before you actually need to use it.
 
z987k said:
You'll go through 10,000 cables before you actually need to use it.
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In the Beeches those things seemed to freeze all the damn time. Cessna I've only had one case and never on a Piper.

I remember something about up and side draft carburetors in the discussion not sure if it was about the carb heat though.
 
I always just used it when I suspected it. Ignorantly with the continentals as well, though I never had one ice up on me. Just do what the manufacturer says is what I say.
 
It's not in the POH and it's not a Cessna. Different airplanes. I don't teach carb heat in a pa28 unless it's needed.
 
Krieger said:
It's not in the POH and it's not a Cessna. Different airplanes. I don't teach carb heat in a pa28 unless it's needed.
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In reality it's not really Cessna, it's 6 cylinder Continentals. All the O-360 and O-320 172s out there don't have the problem.
 
z987k said:
In reality it's not really Cessna, it's 6 cylinder Continentals. All the O-360 and O-320 172s out there don't have the problem.
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Needed it a few times in 4 cylinder Continentals too. Once in a O-320 powered PA18 also. Pressure carb versus float carb is also an issue as to whether it is normal to apply carb heat.
 
MidlifeFlyer said:
Or you could listen to the NTSB based on reports of incident and accidents (some of which are in the ASRS database) where undetected carb ice was a factor that would have been a non-event if "below x power, carb heat on" was a SOP.
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Meh, Undetected Carb. My advice would be to Detect the crap out of carb ice. Pull the heat as needed.

That report is from 1990. I've heard story's of 152's in the 90's having problems with carb ice. Eventually the fleet switched out the Carb Heat Boxes with more effective ones. So I've heard. Can anyone back that up?
 
CFI A&P said:
Needed it a few times in 4 cylinder Continentals too. Once in a O-320 powered PA18 also. Pressure carb versus float carb is also an issue as to whether it is normal to apply carb heat.
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Oh sure, you can get it in any carbed engine, doesn't mean you need it all the time.
 
When I used to instruct for UND (when they still had Warriors), the SOP was "carb heat:on" for every landing (I think it was turned on at midfield downwind), and I don't recall them having any issues with it causing damage.

Personally, I base carb heat use on the conditions for that situation. If it's warm and/or dry enough, I might not use carb heat, but in situations where carb ice is possible, I turn it on whenever I have the power (for a fixed pitch prop) below the green arc for prolonged periods, or at the abeam point in the pattern.
 
Krieger said:
Meh, Undetected Carb. My advice would be to Detect the crap out of carb ice. Pull the heat as needed.
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Yep, and we should get rid of gear warning horns, just put the gear down. Same for various annuciators supplementing gauges.

Detection is kind of the point. Both the NTSB report and the later ASRS carb ice reports tend to involve situations where pilots, for one reason or another, failed to detect carb ice early on. Since we're not all superpilots, those things will happen. But it may be that the SOP of "low power, carb heat on" a la Cessna, might create an association that would lead to earlier detection.

Yes, in a perfect world, everyone would be to "detect the crab out of carb ice." But since we do not live in one, if there is no mechanical downside, the question becomes one of unnecessary-but-harmless vs. preventing-an-accident.
 
Timely accident report on an Aeronca at San Luis Obispo (same airport where I bought my Cessna) that failed to detect carb ice soon enough and application of carb heat was too late. Different airplane, power plant, and phase of flight but still interesting.

NTSB Probable cause: The pilot’s delay in using carburetor heat, which resulted in a loss of engine power due to an encounter with carburetor icing conditions.

http://www.generalaviationnews.com/...m_campaign=1e68e0c788-TP2013&utm_medium=email
 
On the detection vs prevention.... why do we turn on boost pumps? The engine driven fuel pump hasn't failed yet....
 
Krieger said:
It's not in the POH and it's not a Cessna. Different airplanes. I don't teach carb heat in a pa28 unless it's needed.
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And remember, unless it's in Section 2 - Limitations ("Operate carb heat at all times airborne below (__) RPM") it is not regulatory.
 
Krieger said:
Oh the humanity!

You can't compare the two. One is clearly required per the POH.
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As Autothrust said, since it's not limitations it's pretty much a recommendation to begin with.

But your comment interests me. So you don't believe in teaching "best practices" unless they are also in the POH?
 
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