How is stagnation pressure affected as an aircraft gains altitude?

As an aircraft gains altitude, the stagnation pressure decreases due to the reduction in atmospheric pressure with increasing altitude. Stagnation pressure is the pressure a fluid (like air) experiences when it is brought to a complete stop isentropically, meaning without any loss in total energy.

At higher altitudes, the density of the air decreases because the atmosphere thins out. This lower density means that for a given speed, the dynamic pressure (which is a component of stagnation pressure) doesn't increase as much as it would at lower altitudes where the air is denser. Additionally, atmospheric pressure itself decreases with altitude, contributing to a lower stagnation pressure overall.

Thus, as an aircraft ascends, the combination of decreasing air density and atmospheric pressure leads to a decrease in stagnation pressure, aligning with the reasoning behind the correct answer selected.