Commercial Pilot License (CPL) 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice indicates that engine roughness and a drop in manifold pressure are signs of carburetor ice. This phenomenon occurs when moisture in the air freezes inside the carburetor, obstructing airflow and affecting engine performance. As the ice forms, it can restrict the fuel-air mixture entering the engine, leading to a rough running engine characterized by an uneven performance and a noticeable drop in manifold pressure.

In the context of carburetor icing, the conditions leading to these symptoms are typically found in low-temperature and high-humidity environments where the engine's operation leads to a temperature drop in the carburetor due to fuel vaporization. The result is not just a decrease in power but also a distinct change in engine behavior, making roughness and manifold pressure drop key indicators of this issue.

The other options do not accurately align with the indicators of carburetor ice. An increase in fuel flow would typically not be associated with ice formation, as the ice would likely restrict flow rather than enhance it. High RPM without a throttle increase could suggest an issue with engine management or response to throttle input but doesn’t directly indicate ice. Coverage of the engine temperature gauge can occur due to various unrelated reasons and does not specifically indicate carburetor ice.