How does control surface effectiveness change with altitude?

The effectiveness of control surfaces, such as ailerons, elevators, and rudders, is influenced by the density of the air. As altitude increases, the air becomes thinner, meaning there's less air mass surrounding the aircraft. This reduction in air density directly affects the aerodynamic forces acting on the control surfaces.

As air becomes less dense with altitude, control surfaces become less effective because they have a reduced amount of air to generate lift and drag. Consequently, more deflection might be required to achieve the same control response compared to lower altitudes. This can lead to decreased maneuverability and responsiveness of the aircraft, especially during critical phases of flight.

It’s important to understand that while some other factors like aircraft weight, speed, and control surface design play a role in overall performance, the key relationship between altitude and control surface effectiveness is primarily due to the thinner air. This is why the choice indicating that effectiveness may decrease due to thinner air is correct.