Commercial Pilot License (CPL) Practice Exam 2026 - Free Commercial Pilot License Practice Questions and Study Guide

When a pilot experiences a rough-running engine in rain, using carburetor heat as an alternate air source is the appropriate response because it helps mitigate the effects of carburetor icing, which can be exacerbated in humid or wet conditions. The increased moisture in the air can lead to the formation of ice in the carburetor, disrupting the airflow and causing engine roughness. By applying carburetor heat, the pilot can warm the intake air and dissolve any ice that may have formed, thereby restoring normal engine operation and performance.

Increasing engine RPM is not an effective solution because it does not address the underlying issue of potential icing. Reducing altitude immediately may not be safe or effective as it does not specifically resolve the engine issue and could lead to loss of control or other complications. Shutting down the engine could be necessary if the roughness escalates to a critical failure, but the initial step should be to attempt to fix the problem with carburetor heat first. Overall, using carburetor heat is a proactive approach to improving engine performance in adverse weather conditions.