Definition
The two primary performance results that respond to power changes in straight-and-level flight: altitude is the aircraft's vertical position above a reference, and airspeed is the aircraft's speed through the air. In the power-control context, these two values are managed together because a change in power setting affects both, and the pilot must adjust pitch attitude to determine which one changes and which one is held constant.
Plain English
How high you are and how fast you are going through the air. In level flight these two things are linked through power: add or reduce power and one or both will change unless you also adjust pitch.
Context Anchor
Seen in instrument flying when setting or changing power while trying to maintain straight-and-level flight.
Derivation
Altitude comes from the Latin word altus, meaning high. Airspeed is built from air and speed, which helps separate it from speed over the ground: it is speed through the air around the airplane.
Why Pilots Care
Small power changes directly influence whether the aircraft holds its assigned altitude or drifts up or down while airspeed also varies, affecting fuel use, navigation accuracy, and safety margins.
Intuition Check
Do not treat altitude and airspeed as one combined reading. Altitude tells how high the airplane is; airspeed tells how fast it is moving through the air, and a power change can affect both.
Example Sentence 1
Level at 6,000 feet, the pilot reduced power and lowered the nose slightly to maintain altitude and airspeed within tolerances.
Example Sentence 2
During cruise, a slight reduction in power caused the aircraft to lose both altitude and airspeed until pitch was adjusted.