Definition
A condition in which an aircraft's engine does not produce enough power for the aircraft's weight, intended performance, or operating conditions, resulting in sluggish acceleration, poor climb performance, and reduced safety margins.
Plain English
The engine isn't strong enough for the airplane to perform the way it should — climbs are slow, takeoffs are long, and the aircraft struggles in demanding conditions.
Context Anchor
Seen in aircraft performance discussions, takeoff and climb planning, and engine troubleshooting.
Derivation
From 'under-' (less than enough) plus 'powered' (supplied with power). The everyday sense carries directly into aviation: too little power for the job at hand.
Why Pilots Care
An underpowered condition reduces climb performance, limits obstacle clearance, and increases risk during go-arounds or high-density-altitude operations.
Analogy
Like a heavily loaded truck trying to pull a steep grade in too high a gear.
Intuition Check
Underpowered does not mean the engine has no power. It means the available power is not enough for the situation or is less than it should be.
Example Sentence 1
On a hot summer afternoon at a high-elevation airport, the loaded trainer felt underpowered, using nearly the full runway before lifting off.
Example Sentence 2
The pilot decided to remove baggage after realizing the airplane was underpowered for the short, obstructed runway.