What condition is necessary for carburetor icing to occur?

Carburetor icing occurs when a combination of atmospheric conditions contributes to the formation of ice in the carburetor, which can disrupt the air-fuel mixture essential for engine performance. For carburetor icing to manifest, high relative humidity is paramount. When humidity levels are elevated, there is an increased amount of moisture in the air. As the air passes through the carburetor, it is subjected to a drop in temperature due to the vaporization of the fuel. This temperature drop can reach the dew point or even lower, allowing ice to form if the moisture in the air condenses and freezes.

While outside air temperature near freezing and low power settings can contribute to conditions that make icing more likely, they are not the sole prerequisites. High relative humidity is crucial, as it is the moisture that leads to ice formation under the right temperature conditions. Therefore, understanding the role of humidity helps pilots anticipate the risk of carburetor icing and take appropriate measures, like preheating the engine or adjusting operation techniques, to mitigate this hazard.