What are common indications of carburetor icing?

Carburetor icing occurs when moisture in the air condenses and freezes inside the carburetor, disrupting the fuel-air mixture necessary for proper engine operation. One of the most common indications of carburetor icing is a decrease in engine RPM, which can lead to engine roughness. As ice forms, it restricts airflow and can cause the engine to run lean. This results in a drop in power and RPM, often accompanied by a rough running condition as the engine struggles with the disrupted fuel-air blend.

In contrast, signs such as a sudden loss of altitude or fluctuations in airspeed might suggest other issues like turbulence or mechanical failures, rather than specifically indicating carburetor icing. The increase in engine RPM would typically suggest a smooth operation, which is inconsistent with the presence of icing. Therefore, the correct indication of carburetor icing is accurately characterized by the decrease in engine RPM coupled with roughness as the engine is affected by the obstruction caused by ice.