FAA Ground School Practice Test

What is the first indication of carburetor ice in an aircraft with a fixed-pitch propeller?

1. Loss of RPM

2. Increase in engine temperature

3. Engine stall

4. Change in fuel pressure

The correct answer is: Loss of RPM

The first indication of carburetor ice in an aircraft with a fixed-pitch propeller typically manifests as a loss of RPM. Carburetor ice forms when the temperature and humidity conditions within the carburetor drop, often resulting from the vaporization of fuel as it flows through the carburetor throat. This cooling effect can lead to ice formation, which restricts airflow and disrupts the fuel-air mixture, causing a reduction in engine performance. Pilots may notice that the engine begins to lose RPM, which serves as the initial warning sign that the carburetor may be icing up. The other options, while they can occur as the icing progresses, are typically subsequent indicators. For example, an increase in engine temperature may happen later on due to the engine running leaner, but it is not the first sign. Similarly, an engine stall can occur as the ice buildup worsens and significantly impacts engine performance, but this is a more severe consequence. A change in fuel pressure may also occur as a byproduct of the icing, yet it does not directly reflect the initial impact that carburetor icing has on engine RPM. Understanding these dynamics helps pilots recognize and respond to the development of carburetor ice effectively.