Plain English Meaning

The airplane has run low on the two things that keep it flying: speed and height. Once both get too low, there isn't enough of either left to fix the situation.

Full Definition

The loss of an airplane's total mechanical energy — the combined kinetic energy from airspeed and potential energy from altitude — to a level where the airplane can no longer maintain controlled flight or recover from a developing sink rate.

Context Anchor

You will see this term in energy management discussions, especially during , , , , and any situation where the airplane is getting slower, lower, or both.