Certified Flight Instructor Practice Exam – Complete Test Prep 2026

The correct answer is based on the behavior of the engine when carburetor heat is applied in the presence of carburetor ice. When carburetor ice forms, it restricts airflow through the carburetor, which can lead to a drop in engine performance.

When carburetor heat is applied, it warms the air entering the carburetor, which helps melt the ice. This initially causes a decrease in RPM because the engine is now accepting warmer, less dense air. However, as the ice melts and the restriction is relieved, the airflow improves, leading to a gradual increase in RPM as the engine regains power.

This behavior is characteristic of how carburetor heat works to correct the issue of icing, making the observation of a decrease followed by a gradual increase in RPM a clear indicator of the effectiveness of the carburetor heat in resolving carburetor ice.

Monitoring the RPM during this process is critical; if no change in RPM is noted, or if there is an increase without prior decrease, it may indicate that there was no ice present initially. Thus, recognizing the pattern of initial decrease followed by an increase distinctly points to the presence of carburetor ice that is being resolved by the application of heat.