Which of the following is NOT a critical surface when considering frost or ice?

In aviation, certain surfaces of an aircraft are crucial for maintaining aerodynamic performance and control, especially in adverse weather conditions like frost or ice. The wings, control surfaces, and propeller blades are all critical areas because even a small accumulation of ice can significantly affect lift, control responsiveness, and thrust.

Wings are essential for generating lift, and ice can drastically change their shape, leading to a loss of performance. Control surfaces, which include ailerons, elevators, and rudders, are vital for maneuverability. Any obstruction due to frost or ice can hinder their effectiveness, making it difficult to control the aircraft. Propeller blades are critical as well, because ice accumulation can reduce thrust and could lead to inefficient engine operation.

In contrast, while landing gear is important for takeoff and landing phases, it does not impact the aircraft's aerodynamic properties directly during flight. Therefore, it is not considered a critical surface in the same way that the other components are when evaluating the effects of frost or ice. This distinction is crucial for pilots to ensure safe flight operations and to prioritize de-icing measures where they are most needed.