Under what atmospheric conditions is carburetor icing most likely to occur?

Carburetor icing is most likely to occur in conditions where humidity is present, specifically in humid air with temperatures that fall between 20°F and 70°F. In these conditions, the combination of the temperature range and moisture content facilitates the formation of ice within the carburetor.

When air passes through the carburetor, it expands and cools. If the air is humid, the moisture can condense and freeze, leading to ice accumulation. The temperature range of 20°F to 70°F is particularly critical because it is within this range that the temperature is low enough to promote ice formation but not so low that air is simply frozen solid, which would be less likely in warmer or dryer conditions.

In contrast, cold and dry conditions are typically less conducive to carburetor icing because the lack of moisture means there is minimal opportunity for ice to form. Similarly, warm and dry or warm and humid conditions do not fall into the most likely range for icing; while humidity can contribute to icing, the higher temperatures in these scenarios mitigate the risk of ice formation. Thus, the specific combination of humid air and the moderate temperature range is ideal for carburetor icing to occur.