What happens to Vx as altitude increases?

Vx, or the best angle of climb speed, is primarily affected by the performance characteristics of the aircraft and environmental factors such as air density. As altitude increases, the air density decreases, which has a direct impact on lift generation. At higher altitudes, the reduced air density means that the wings have a harder time generating the same amount of lift at a given airspeed compared to lower altitudes.

To maintain efficient climb performance, pilots must adjust their speeds, and in many cases, Vx will actually increase slightly because the aircraft needs more speed to produce sufficient lift in less dense air. Therefore, the correct answer indicates that as altitude increases, Vx does indeed increase due to the decreased air density impacting lift over the wings. This is essential for pilots to understand in order to optimize their climb performance based on conditions they face during flight.