FAA Ground School Practice Test

During a high altitude run-up, what symptom could suggest carburetor ice?

1. Increase in fuel pressure

2. Fluctuations in RPM

3. Engine roughness

4. Stable RPM

The correct answer is: Engine roughness

Carburetor ice forms in conditions of high humidity and low temperatures, which can lead to a significant drop in engine performance. One of the primary symptoms that indicates carburetor ice is engine roughness. As ice forms in the carburetor, it restricts airflow and disrupts the proper fuel-air mixture, causing fluctuations in engine performance. This roughness manifests as irregular engine operation or a noticeable decrease in power, which pilots can easily feel during operation. Understanding the aircraft's response to carburetor ice is critical for pilots, as early detection can lead to corrective actions, such as applying heat to the carburetor, to restore proper function. The roughness of the engine serves as a clear indicator that something is amiss, prompting the pilot to investigate further.