What happens to engine RPM when carburetor heat is applied if icing is present?

When carburetor heat is applied in the presence of icing, the engine RPM behavior can be understood by considering the effects of heat on the carburetor and the air-fuel mixture. Initially, the application of carburetor heat tends to introduce warmer air into the carburetor. This warmer air can reduce the density of the air-fuel mixture, impacting combustion efficiency momentarily.

As the carburetor heat melts the ice, the resulting change in air density may lead to a slight drop in RPM initially due to a richer mixture. However, as the ice melts and normal airflow resumes, the engine can draw in a proper air-fuel mixture, resulting in improved combustion. This contributes to a gradual increase in RPM as the engine compensates for the initially affected fuel-air ratio.

Thus, the correct option reflects the initial drop followed by a recovery as the ice is cleared and normal operation is restored. Understanding this process is key to managing engine performance in conditions that may lead to carburetor icing.