Definition
The amount of thrust available beyond what is required to maintain level, unaccelerated flight at a given airspeed. Excess thrust is what the airplane uses to climb; the steepest climb angle occurs at the airspeed where excess thrust is greatest.
Plain English
It is the spare push the engine has left over after pushing the airplane forward through the air. That leftover push is what lets the airplane climb at an angle.
Context Anchor
Seen in climb performance discussions and angle-of-climb charts, especially when comparing the speed for the steepest climb with the thrust the airplane has available.
Derivation
Excess comes from the Latin excedere, meaning to go beyond. Here it means the thrust that goes beyond what is needed for straight-and-level flight. That leftover thrust is what is available for climbing.
Why Pilots Care
It sets the steepest climb angle an airplane can achieve, which matters for clearing obstacles after takeoff.
Grounding Statement
If the airplane needs some of its engine push just to keep flying level, thrust excess is the part left over that can help it climb.
Intuition Check
Excess does not mean wasted or unnecessary here. It means extra thrust available for performance, especially climbing.
Example Sentence 1
The airplane climbs at its steepest angle at the airspeed where thrust excess is greatest.
Example Sentence 2
At higher airspeeds the thrust excess drops and the climb angle becomes shallower.