Certified Flight Instructor - Flight Instructor Airplane Practice Exam

What impact does carburetor heat have on engine performance during takeoff?

1. Increases power output significantly

2. Does not affect performance

3. May cause engine roughness

4. Can increase takeoff distance

The correct answer is: May cause engine roughness

The use of carburetor heat during takeoff can significantly impact engine performance, particularly leading to potential engine roughness. When carburetor heat is applied, it introduces warmer air into the engine's intake system. This is designed to prevent carburetor icing, which can occur under certain atmospheric conditions, particularly with high humidity and low temperatures. However, the warmer air is less dense than cooler air, which can result in a decrease in engine efficiency and power output. Consequently, if too much carburetor heat is applied, especially during takeoff when maximum power is needed, the engine may not perform as expected. The mixture becomes richer due to the warmer air, which can lead to a rough running engine or even a momentary loss of power. This roughness can be more pronounced during the critical phases of flight like takeoff, when pilots require a stable and powerful engine to ensure safe climb-out. In some instances, if the temperature changes significantly, adding carburetor heat could lead to a further decrease in performance, reflected in a longer takeoff distance. However, it is primarily the potential for engine roughness that is most critical during this phase of flight, demonstrating why carburetor heat should be applied judiciously, keeping