What occurs when carburettor heat is applied and ice is present?

When carburettor heat is applied in the presence of ice, the effect on manifold pressure and engine performance is well understood in aviation mechanics. The primary purpose of applying carburettor heat is to melt any ice that may have formed in the carburettor throat due to the evaporation of fuel and the resulting cooling effect, which can lead to significant performance issues.

When the heat is applied, the initially cold air-fuel mixture becomes warmer as it flows through the heated components. This warming effect typically results in a richening of the fuel mixture because warmer air can hold more moisture and often leads also to a drop in air density, which decreases engine performance temporarily. Initially, this can create an immoderate drop in manifold pressure, as the engine temporarily struggles to maintain its suction and efficiency while the ice melts.

Once the ice is melted, the manifold pressure tends to stabilize and may return to normal levels, albeit often at the expense of a richer mixture. Therefore, option A captures the full process accurately: it describes the initial drop in manifold pressure associated with the application of carburettor heat when ice is present, the transition to stabilization of that pressure, and the associated changes in the mixture. This understanding is critical for pilots