What is the first symptom of carburetor icing?

The first symptom of carburetor icing is typically a decrease in RPM. This happens because carburetor ice restricts airflow through the carburetor, creating a situation where the engine can receive less fuel and air mixture. As a result, the engine may not operate smoothly, leading to a gradual reduction in RPM.

Carburetor icing occurs due to the loss of heat when fuel evaporates and the air passing through the venturi of the carburetor, which can lead to conditions conducive for ice to form, especially in humid conditions at temperatures around or below freezing. This initial decrease in RPM can be a crucial indicator of the presence of carburetor ice, prompting the pilot to take corrective action to mitigate the icing before it leads to greater issues such as engine roughness or even engine failure.

The other symptoms mentioned may follow after the initial RPM decrease but are not the first indicator. Understanding the specific sequence of symptoms is key for pilots to effectively manage and respond to carburetor icing conditions.