Final answer:
The altitude of the airplane preparing to land is 46,400 feet above the airport, which is a direct measurement of its height above ground level.
Step-by-step explanation:
The question you're asking is regarding the altitude of an airplane. If an airplane is preparing to land and it is 46,400 feet above an airport, then its altitude is 46,400 feet. In other contexts, altitude refers to the vertical distance of an object from a specific reference point, typically sea level or the surface of the Earth. Thus, the altitude of the airplane in your question is a straightforward measurement of its height above the ground (specifically, the airport).