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4 Answers

CARB HEAT & MAGNETO CHECK ON GRASS

Asked by: 1563 views Student Pilot

Hi guys ,just a quick question.

Why are we discouraged from doing a carb heat & dead cut check during  engine run-up on grass? 

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4 Answers

  1. Best Answer


    Kris Kortokrax on Feb 29, 2020

    That’s a good question. You should ask the person who told you this. Have that person show you something to justify his procedure.

    I learned to fly at an airport with only grass runways. Later, I flight instructed at an airport with only a grass runway. We always checked carburetor heat during runup and I always did a grounding check for the magnetos. Never had any problems.

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  2. KDS on Feb 29, 2020

    As Kris wrote, it would be good to ask the person who told you that.

    However, I’ll take a stab at what the person’s answer will be.

    Carburetor heat is unfiltered air. They may be concerned about ingesting debris such as newly mown grass.

    For the dead cut check (what I would call the broken p lead check), the concern may be that a backfire could set the grass on fire.

    Hopefully you’ll get back with us after asking those questions and let us know what he or she said.

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  3. Kris Kortokrax on Feb 29, 2020

    If your instructor is concerned that the engine will ingest newly mown grass, he is unfamiliar with the plumbing on the engine. The inlet for air for carburetor heat is behind the prop. The air then flows through scat tubing to the muffler and then through the muffler shroud, where it picks up heat, then through more scat tubing to the carburetor. It is unlikely that blades of grass (if they were able to be picked up and blown into the opening behind the prop) would survive the journey to the carburetor.

    As to a backfire setting the grass on fire, if the mag grounding check is done at idle (as it should be), the engine will not backfire. If the engine did backfire, I would be much more concerned about blowing out the seams on the muffler. Just for kicks, take a lit propane torch and touch it to the grass for the split second that a backfire would last. See what kind of fire you could ignite.

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  4. ayavner on Mar 03, 2020

    Another possibility here is not so much the risk of ingesting or setting fire to grass, but the fact that if you are on a grass/dirt strip, there may be concern about throwing stones or nicking the blades at the higher RPM used for the run-up checks. Only other thing I can think of.

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