Final answer:
Vertical locations on an airplane are made in reference to the Earth or the airplane itself, primarily for safety and navigation purposes, ensuring that air traffic control can maintain a safe vertical separation between aircraft.
Step-by-step explanation:
Vertical locations on an airplane are made in reference to a specific reference frame, typically the Earth or the airplane itself. The vertical component of an airplane's movement, whether it's climbing or descending, is usually measured with respect to the Earth's surface as the reference frame. The altitude of the airplane, which is the vertical distance from the Earth's surface, is tracked by air traffic control using various instruments like altimeters, and it's regulated by organizations like the Federal Aviation Administration, which stipulates that each airplane must maintain certain vertical separation from other aircraft to ensure safety.
When considering the motion of an object, such as an airplane or its passengers, a reference frame must be established. For example, to describe the position of an airplane, one can use its position relative to the Earth. Additionally, in the specific case of the two aircraft monitored by an air traffic controller, finding the position vectors relative to the control tower and calculating the distance between them at a certain moment would involve mathematical operations in physics.