During engine operation, what can be a sign of carburetor icing?

Intermittent roughness in engine operation is a key indicator of carburetor icing. Carburetor icing can occur when moisture freezes inside the carburetor due to the drop in temperature caused by the fuel vaporization process. As ice builds up, it can lead to a restricted airflow and uneven fuel delivery, causing the engine to run roughly or produce intermittent roughness as it struggles to maintain steady operation.

The phenomenon occurs primarily in conditions where the temperature is between 20°F and 70°F with high humidity, making it more prevalent during cool, moist weather. The roughness can manifest as fluctuations in engine RPM or a rough running engine that can sometimes even resolve briefly as the ice melts and temporarily clears the airflow, only to reoccur as more ice builds up.

Other indicators of carburetor icing may include a noticeable drop in RPM if the icing is severe, but intermittent roughness is often one of the first signs a pilot may notice. Hence, recognizing and responding to this symptom is vital for maintaining engine performance and safety during flight.