What is a primary effect of icing on an aircraft?

Icing significantly disrupts the flow of air over the airfoils of an aircraft, which can lead to a variety of performance issues. When ice accumulates on the wings and control surfaces, it alters the aerodynamic shape, increasing drag and reducing lift. This disruption can change how the air behaves around the wing, leading to earlier stall conditions, and negatively impacting the overall stability and control of the aircraft.

Understanding this effect is crucial for pilots, especially in conditions where icing is a risk, as it highlights the importance of monitoring for icing conditions and employing de-icing or anti-icing measures to ensure safe flight operations. The other options misrepresent the impact of icing: it does not decrease stall speed or increase lift and is not limited to affecting fuel efficiency.