Definition
The amount of power the engine and propeller combination can actually deliver to the airplane at a given moment, under the current conditions of altitude, temperature, airspeed, and throttle setting. It is the usable output of the powerplant, not the maximum it could ever produce.
Plain English
How much power the engine can give you right now, in the conditions you are actually flying in.
Context Anchor
Seen in airplane performance discussions, especially when comparing how much power the airplane can produce with how much power it needs for level flight or climb.
Derivation
Power comes from an older idea meaning the ability to do work. Available means able to be used. In this term, the useful idea is not the engine’s advertised maximum rating, but the power actually usable by the airplane in the current flight condition.
Why Pilots Care
It sets the upper limit on climb performance and the range of speeds at which level flight is possible.
Grounding Statement
On a hot day at a high airport, the airplane may run normally but still have less power available for takeoff and climb.
Intuition Check
Do not read “available” as “extra” or “in reserve.” Power available means the total usable power the airplane can produce in that condition; only the part left after meeting the airplane’s current need is extra power.
Example Sentence 1
On a hot, high-altitude day, power available was so reduced that the airplane could barely maintain a 200 foot-per-minute climb.
Example Sentence 2
The points where the power-available curve crosses the power-required curve mark the maximum and minimum speeds for level flight.