When should carburetor heat be used?

Using carburetor heat is essential to prevent icing in the carburetor, which can cause power loss, especially in conditions that promote icing, such as when flying in temperatures below about 70 degrees Fahrenheit with high humidity. The correct answer indicates that carburetor heat should be applied when icing is occurring and power loss is experienced because this action helps clear ice that has formed within the carburetor.

The application of carburetor heat warms the incoming air, which can melt accumulated ice and restore proper fuel-air mixture, thus improving engine performance and preventing further power loss. It’s particularly crucial in warmer atmospheric conditions with high moisture content, where icing is more likely to happen despite surface temperatures being above freezing.

This is why it's not advisable to use carburetor heat continuously during all phases of flight or when power is stable, as doing so may actually degrade engine performance by introducing warmer, less dense air, which can lead to a richer fuel mixture and potential loss of power under normal operations when no icing is present.