Soar to New Heights with the 2026 Commercial Pilot License (CPL) Practice Exam – Ready for Takeoff!

Using cabin heat as an alternate air source is correct because it allows the pilot to potentially bypass any ice formation in the carburetor or other components caused by high humidity and low temperatures associated with heavy rain. When rain is heavy, there's a chance of water ingestion in the engine, and the use of cabin heat can help ensure that warmer, drier air enters the engine system. This action can help maintain engine performance and prevent further complications due to engine roughness.

While other measures, such as climbing to a higher altitude or adjusting throttle, may seem like viable options, they do not specifically address the immediate concern of engine roughness due to potential icing or moisture issues. Turning off the carburetor heat could exacerbate the problem by allowing colder air that might contribute to icing or rough engine operation. Therefore, using cabin heat is a proactive and sensible response in this scenario.