The presence of carburetor ice in an aircraft equipped with a fixed-pitch propeller can be verified by applying carburetor heat and noting

• A. A. a decrease in RPM and then a gradual increase in RPM.
• B. B. an increase in RPM and then a gradual decrease in RPM.
• C. C. a decrease in RPM and then a constant RPM indication.

Answer: (A)

The presence of carburetor ice can be confirmed by applying carburetor heat and observing the engine's RPM response. When carburetor ice forms, it restricts airflow through the carburetor, leading to a decrease in engine power output and RPM. When carburetor heat is applied, the ice begins to melt, and the airflow is restored, resulting in a gradual increase in RPM as the engine regains power.

Initially, when carburetor heat is applied, you will notice a decrease in RPM because the heat can cause a momentary disturbance in air-fuel mixture due to the introduction of warmer air. However, as the ice melts and normal airflow is restored, the RPM will gradually increase as the engine regains full power and efficiency. This sequence of a decrease followed by an increase in RPM confirms the presence of carburetor ice and demonstrates the effectiveness of using carburetor heat to address the issue.