FAA Ground School Practice Test

What condition is most favorable for carburetor icing to develop?

1. Cold temperatures and low humidity

2. Temperature between 20 and 70 degrees and high humidity

3. Warm temperatures and low humidity

4. Dry air and high altitude

The correct answer is: Temperature between 20 and 70 degrees and high humidity

Carburetor icing is most likely to occur under conditions where the temperature is moderate, specifically between 20 and 70 degrees Fahrenheit, combined with high humidity. When the air is moist, the water vapor present can condense within the carburetor. This condensation of moisture, combined with the cooling effect that occurs when fuel vaporizes, can lead to ice formation if the air temperature is within that certain range. In this situation, the temperature is cool enough to facilitate icing, while high humidity ensures that there is sufficient moisture available to form ice. As the engine draws in air and fuel, the temperature drop from the fuel's vaporization increases the likelihood of freezing water vapor, which can obstruct the carburetor and disrupt the engine's operation. Other conditions, such as cold temperatures with low humidity or warm temperatures with low humidity, do not create as favorable an environment for carburetor icing, because either the lack of moisture or the warmer temperatures significantly reduce the ice formation potential. Similarly, dry air at high altitudes lacks the moisture needed for icing to occur.