ok, here's the energy deal, kinetic energy is the energy of motion. It depends on the mass and velocity of the object. Changing the velocity of the object will have a great effect on the energy.
there are 2 types of potential energy, elastic and gravitational. Since airplanes cant stretch elastic is out leaving us gravitational. Gravitational energy depends on weight and height.
so, here's the formula's:
Kinetic energy = mass x velocity(squared) divided by 2= KE
Gravitational potential energy= weight x height = GPE
Now, looking at these formulas there is no way a plane that converts kenetic energy into gravitational potential energy then agian converts to kenetic energy catch a plane in steady kenetic energy status. Now there is one variable to this and that is the speed of the two planes. The plane that conducts this move must be moving at an average of 150 mph faster than the steady kinetic plane. Also if the loop is started far in advance of the plane than it is reasonable that the looping plane will come down with a potential kill shot from above. BUT, if the planes passes one another as in a head on, then there is no way a plane should be able to loop converting his E twice catch up and kill the other plane. Does that make sence to anyone?