Final answer:
A heavyweight airplane is defined as an airplane with a gross weight above the normal landing weight.
Step-by-step explanation:
A heavyweight airplane is defined as an airplane with a gross weight above the normal landing weight. The weight unit typically used for airplanes is pounds. Therefore, the answer to the question is that heavyweight airplanes have a gross weight above the normal landing weight of a certain number of pounds, which is not specified in the given information.