Certified Flight Instructor - Flight Instructor Airplane Practice Exam

Which statement about carburetor icing is true?

1. The first indication of carburetor icing is a decrease in manifold pressure.

2. Carburetor icing forms best when the air temperature is between -7 °C and 21 °C with visible moisture.

3. Carburetor icing will form whenever the ambient temperature is below freezing.

4. Reduced throttle settings prevent carburetor icing.

The correct answer is: Carburetor icing forms best when the air temperature is between -7 °C and 21 °C with visible moisture.

The statement that carburetor icing forms best when the air temperature is between -7 °C and 21 °C with visible moisture is accurate because this range is critical for the formation of icing in the carburetor. In this temperature band, the conditions are conducive to icing as the water vapor in the air can condense and freeze within the carburetor, which disrupts the airflow and can lead to engine performance issues. Moisture, whether it is from humid air or precipitation, acts as a medium where the temperature drop associated with fuel vaporization causes the moisture to freeze and form ice. Carburetor icing does not necessarily occur below freezing; it can indeed form in temperatures above freezing when there's enough moisture present. This distinction is crucial for pilots to understand, as it highlights the need to be vigilant about carburetor icing conditions even when temperatures seem moderate, but air humidity is high. The other statements do not accurately capture the conditions for carburetor icing formation. For example, a decrease in manifold pressure may not always be the initial signal of icing and can occur for various operational reasons. Also, reduced throttle settings can actually contribute to icing by decreasing airflow and temperature within the carburetor, making it more susceptible to