Why might an aircraft require higher speed at high altitudes?

An aircraft requires higher speed at high altitudes primarily to generate sufficient lift. As altitude increases, the air becomes less dense, which means there are fewer air molecules available to create lift. Lift is generated according to the lift equation, which incorporates factors such as air density, velocity, wing surface area, and the lift coefficient. Since the density of air decreases with altitude, an increase in the aircraft's speed is necessary to compensate for this reduction in density to maintain adequate lift.

At high altitudes, the aircraft's wings need to move through the air more rapidly to produce the same amount of lift that would be generated at lower altitudes where the air is denser. This is crucial for maintaining stable flight and avoiding stall conditions, where the aircraft could lose lift and result in an unsafe situation. Therefore, achieving and sustaining a higher speed helps ensure that the aircraft can handle the challenges posed by the thinner air at elevated heights.