Definition
A delay between the pilot's throttle input and the engine's actual change in power produced. In turbocharged and turbine engines especially, advancing the throttle does not produce an immediate increase in thrust or horsepower; the engine takes time to spool up and deliver the commanded power.
Plain English
When you push the throttle forward, the engine doesn't respond instantly. There is a short delay before the power you asked for actually shows up.
Context Anchor
Seen in engine handling discussions, especially when changing power for takeoff, approach, landing, or a go-around.
Derivation
Lag means to fall behind or come later than something else. Here, the power produced by the engine comes slightly after the pilot’s control movement.
Why Pilots Care
The lag can cause over-controlling or insufficient power response during critical maneuvers if the pilot does not anticipate it.
Analogy
It is like turning on a large fan: the switch moves right away, but the fan takes a moment to speed up.
Grounding Statement
Move the power control now, and the full engine response may arrive a moment later.
Intuition Check
Do not assume the airplane is ignoring the power control. The key idea is delay: the command happens now, but the actual power change follows shortly after.
Example Sentence 1
Because power output lags in this turbocharged engine, the pilot began the go-around earlier than they would have in a normally aspirated airplane.
Example Sentence 2
At high altitude the pilot planned for power output lags when leveling off so the airspeed did not drop below target.