FAA Powerplant Written Practice Test

Where is one common source for carburetor air heat derived from?

1. Cold ambient air

2. Warm ducted air from around the exhaust system

3. Air conditioning system

4. Direct engine output

The correct answer is: Warm ducted air from around the exhaust system

One common source for carburetor air heat is derived from warm ducted air around the exhaust system. This heated air is used to prevent the formation of ice in the carburetor, which can occur when the engine draws in cold air, especially in high humidity conditions or during specific flight operations. Using warm air from around the exhaust system helps maintain an optimal mixture of air and fuel entering the engine, ensuring efficient combustion and preventing power loss due to ice blockage. This method of sourcing heat is particularly beneficial during takeoff and climb phases when the engine is most vulnerable to carburetor icing. The other options do not provide effective sources of heat for carburetor air. Cold ambient air would not help prevent icing, as it would exacerbate the problem. An air conditioning system does not typically supply warm air to the carburetor, and direct engine output doesn't relate to sourcing heat for the carburetor but rather refers to the overall mechanical power produced by the engine.