What is the first indication of carburetor ice?

The first indication of carburetor ice is indeed a drop in RPM. Carburetor ice forms when there is a combination of moisture in the air and a significant drop in temperature as the fuel vaporizes in the carburetor. When ice begins to form, it restricts airflow to the engine, often resulting in a decrease in RPM. This symptom is typically one of the earliest observable signs that an issue is developing, allowing the pilot to take corrective action, such as applying carburetor heat to melt the ice and restore proper engine function.

Understanding this phenomenon is crucial for pilots, as recognizing the early signs of carburetor ice can prevent further reduction in performance and ensure the safety of flight. Other options, while related to engine performance, don't represent the initial warning sign that a pilot might experience during flight when carburetor ice is present.