First of all, energy is used to do work, which is defined by a change in position. Energy is constantly being converted from potential to kinetic to potential, and so on, depending on its location and what's being done to it.
An airplane in flight has both kinetic and potential energy, and they are present in more than one way:
- Kinetic energy, or that caused by the plane's motion. The airplane moving is like a waterfall in cascade. The water hitting something else will have enough energy to change its position (displacing it, thereby doing work).
- Potential energy, or that used by the plane's position so high above the ground. The airplane's position in the air carries with it the potential for the plane to do work on whatever is below it, were it to (let it not be so) fall from the sky. This is just as the water above the cascading falls has the potential, because of its location, to do work.
- More potential energy, caused by the chemical energy in the structure of bonds in stored gasoline and batteries with the potential to do work...
- More kinetic energy through the combustion of gasoline as the plane accelerates and moves.
As the plane rises and falls and accelerates and decelerates, the potential and kinetic energy change accordingly.