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7 Answers

Carburetor heat

Asked by: 7934 views ,
Commercial Pilot, Flight Instructor, General Aviation, Instrument Rating, Private Pilot, Student Pilot

There is an instructor in my school, whose been instructing for over 4 years now. He told me that Cessna's require the use of carb heat on the landing checklist for insurance purposes only and not for carburetor icing. He also said we fly in Texas, where it is usually very hot, and very little moisture is present. My questions is,"Is the statement about the insurance true or do we really use it for carb ice?

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7 Answers

  1. Best Answer


    Mark Kolber on Oct 30, 2014

    It is a lot of fun to blame insurance companies and lawyers for everything, and POH checklist instructions are no exception.

    Gleaned from discussions (I am no mechanic, far from it) the Cessna recommendation for using carb heat as a preventive measure comes from the placement of the carburetor in the engine block when compared with Pipers, where the recommendation is only to use carb heat as needed.

    But here’s something to share with your instructor and get his thoughts. It is a 1990 Safety Recommendation (PDF) from the NTSB that carb heat should always be used as a preventive in carbureted aircraft engines, regardless of make or model.

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  2. Russ Roslewski on Oct 30, 2014

    The POH certainly requires it.

    Anybody can make a checklist (in fact, it’s a great exercise for a student to do, to really get in the POH and learn the airplane). Is it his contention that it really doesn’t need to be on the checklist that your school uses, but the school keeps it on for the always vague and unsatisfying answer of “insurance purposes”?

    I’ve never heard this argument before, and it seems silly (and dangerous). Yes, it’s hot in Texas, but carb heat should be a standard part of your pre-landing checklist in that airplane. Carb ice DOES form, and do you know whether the exact conditions at that moment on that flight are conducive to ice forming or not? Of course not – so just add the carb heat. To do anything else is foolhardy.

    Develop a good habit, that way you won’t forget it when you really need it.

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  3. Sam Dawson on Oct 30, 2014

    I have gotten carb heat in El Paso, TX in the summer in a 182 after a long descent from high altitude.
    Turning carb heat on does not hurt anything. Not having carb heat on when you need it, however, can be catastrophic, especially at low altitude. This is why I find the Piper recommendation to use carb heat as needed to be comical- finding out you need it at 50′ during a go around can be deadly.

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  4. Kris Kortokrax on Oct 30, 2014

    Take a look at the icing probability chart at this link:
    http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgSAIB.nsf/dc7bd4f27e5f107486257221005f069d/f319315cfc90c3f7862575e500439fa0/$FILE/CE-09-35.pdf

    Conditions today at DFW – temp 71 / dew point 46, HOU temp 73 / dew point 55, ELP temp 69 / dew point 39. These combinations place you in the green area of the chart which would indicate serious icing probability at glide power (think approach to land).

    Next, Google images for Lycoming O-320 or O-360 and compare them to images for a Continental O-200. Pay attention to where the carburetor is mounted. On the Lycoming, it is bolted to the bottom of the oil sump (think hot oil). The carburetor on the Continental engine is not attached in this manner. This makes it more susceptible to carburetor ice. This is what Mark was alluding to.

    Please, follow the instructions in the POH. Ask your instructor to provide you with objective evidence from Cessna and Continental that you can ignore the POH.

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  5. psequeira on Oct 30, 2014

    Thanks a ton Kris,Sam, Russ and Mark for all the info

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  6. Bob Watson on Nov 03, 2014

    Remember that the air inside the carb is cooler than the ambient air due to the air expanding after the venturi and the fuel vaporization.

    On approach to landing, you could probably get away with not using the carb heat, because you’ll have the engine power reduced anyway. But if you need to go around (or taxi off the runway), those could be difficult if your carb is blocked by ice. Bottom line, if the POH says you should, you should.

    In the Cessnas, it’s more effective to apply it early in the pattern, while the engine is still producing power, because the heat comes from the exhaust pipe (by way of a shroud, IIRC, not the exhaust directly). If you apply the heat on short final when the engine is at, or near, idle, it won’t be very effective–something you would find out when you try to go around.

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  7. Frank Minich on Jan 13, 2018

    Even in Texas, it sometimes gets cold! What should one do if the air outside is at or below freezing and there’s no visible moisture? Check the chart and use carb heat only if the temperature/dew point is in the shaded area?

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