What effect does applying carburettor heat have on a CSU-equipped engine with carburettor ice?

When carburettor heat is applied to an engine that has developed carburettor ice, the heat warms the air entering the carburettor. Initially, this can lead to a drop in manifold pressure. The reason for this decrease is that the introduction of heated air changes the air density and may disrupt the airflow, momentarily causing a reduction in engine power and hence lowering manifold pressure.

As the carburettor ice begins to melt due to the increased temperature, the airflow becomes more efficient, leading to an increase in manifold pressure as the engine gains back its performance. This process is crucial because it effectively removes the ice obstruction that causes rich fuel mixtures and fluctuating engine performance.

Understanding this behavior is essential for pilots, as managing carburettor heat is a key strategy in preventing or mitigating the effects of carburettor ice during flight operations. Proper use of carburettor heat can help restore proper engine performance after an ice event has occurred.