My understanding is that kinetic energy is the work done to accelerate the mass of the a/c. This is increased by engine thrust or trading potential energy (losing altitude and claiming the acceleration from gravity). If you have low PE and low KE then total energy is low which is very dangerous.
Update: Boeing have a good description here...
Aerodynamic Principles of Large-Airplane Upsets (Aero Magazine, 1998 Q3 edition)