What are the symptoms of carburettor icing when cruising in a fixed-pitch propeller equipped aircraft?

The symptoms of carburettor icing in a fixed-pitch propeller-equipped aircraft primarily manifest as an increase in manifold temperature, a decrease in RPM, and a loss of airspeed.

When carburettor icing occurs, ice forms in the carburettor, obstructing airflow and disrupting the fuel-air mixture necessary for combustion. This results in an increase in manifold temperature because the reduced airflow causes the engine to draw in more heat from the combustion process. Consequently, the decrease in RPM is due to the engine struggling to produce the power needed to maintain a steady speed, as the blockage caused by ice limits airflow and fuel delivery. Increased ice buildup ultimately leads to a loss of airspeed since the aircraft cannot maintain the required thrust to stay at cruising speed.

The understanding of these symptoms is vital for pilots, as recognizing carburettor icing can lead to timely corrective actions, ensuring the safety and efficiency of flight operations.