Private Pilot License (PPL) Aircraft General Knowledge (AGK) Practice Test

When carburetor heat is applied and ice is not present, what happens to engine RPM?

Drop because the mixture becomes rich Rise Stay the same Fluctuate

Correct Answer:

Drop because the mixture becomes rich

Explanation:

Carburetor heat introduces warmer, less dense air into the intake. For a given throttle setting, the volume of air entering the engine is about the same, but the mass of that air is reduced. The carburetor meters fuel in response to air flow, so with less dense air the fuel flow doesn’t decrease proportionally, making the mixture richer. A richer mixture reduces combustion efficiency and power, so engine RPM tends to drop when carb heat is applied even if there’s no ice present.

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