Insidious Icing

Tuesday, April 20, 2021 at 09:34 AM ET

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Key Takeaways:

Carburetor ice is a frequent cause of engine stoppage, often occurring during low-speed flight or partial throttle settings, as the author experienced.
Ice primarily forms on the butterfly throttle valve, downstream of the venturi, due to fuel evaporation cooling, especially when the throttle is partially closed.
To prevent carburetor ice, pilots should apply carb heat during descents, lower-speed cruise in humid conditions, or when visible moisture is present, adjusting the mixture as needed when using carb heat in cruise.

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I was tootling along at low speed in my little experimental, leaning out the Marvel-Schebler carburetor one nice day, when the engine suddenly stopped. I immediately went through the restart procedures, but to no avail. Realizing that I had run out of options, I turned my little Sonex into the wind and landed on a hillside recently planted in wheat. I was later able to take off from a nearby highway and fly back to the airport. Nature had been kind to me.

The throttle setting was relatively low, and the temperature-dew point spread was not too high either. It must have been carburetor ice!