How does VMC change at different altitudes?

The correct choice indicates that the value of VMC, which stands for Minimum Control Speed, decreases as altitude increases. This phenomenon occurs because, at higher altitudes, the air density is lower, which affects the performance characteristics of an aircraft.

As you climb to higher altitudes, the reduced air density results in decreased engine performance and less available thrust. The aileron effectiveness diminishes due to the less dense air, which can lead to a lower VMC. This means that the minimum speed at which a pilot can maintain controlled flight after experiencing an engine failure becomes lower as altitude increases.

In contrast, at sea level, VMC is higher because the denser air provides better control responsiveness, and the aircraft requires a higher speed to maintain control following an engine failure. Therefore, understanding how VMC changes with altitude is crucial for pilots when operating at varying flight levels, particularly during critical phases of flight like takeoff and climb.