FAA Ground School Practice Test

Carburetor icing can occur at an OAT as high as what temperature?

1. 20 degrees Celsius with high relative humidity

2. 10 degrees Celsius with low humidity

3. 30 degrees Celsius with low humidity

4. Only at freezing conditions

The correct answer is: 20 degrees Celsius with high relative humidity

Carburetor icing can indeed occur at temperatures as high as 20 degrees Celsius, particularly when relative humidity is high. This phenomenon occurs because the carburetor's operation can lead to a drop in temperature as fuel vaporizes. The cooling effect can be significant enough to cause moisture in the air to freeze into ice, which can obstruct the airflow through the carburetor. Moist air contains more water vapor, which increases the likelihood of icing because it can condense and freeze in the cold conditions created by the carburetor's function. Therefore, when the outside air temperature is around 20 degrees Celsius and the humidity is high, the risk of carburetor icing is a concern for pilots. Understanding the relationship between temperature, humidity, and the mechanics of carburetor operation is crucial for maintaining safe flight operations, especially in conditions that may seem benign based on temperature alone.