Definition
A condition in which the ball of the inclinometer (the slip-skid indicator) rests in the middle of its glass tube, between the two reference lines, indicating that the airplane is in coordinated flight with no sideways slipping or skidding.
Plain English
The little ball in the cockpit instrument is sitting right in the middle, which means the airplane is flying straight through the air without sliding sideways.
Context Anchor
Seen on the instrument panel during stall practice, slow flight, and turns when the pilot checks that rudder use is keeping the airplane coordinated.
Derivation
“Slip” and “skid” come from everyday ideas of sliding. In aviation, they describe two different ways an airplane can move sideways instead of cleanly through the air. “Centered” means the indicator ball is in the middle, which is the quick cockpit sign that the sideways motion is under control.
Why Pilots Care
Keeping the slip-skid indicator centered during stalls prevents entry into an unintentional spin by maintaining coordinated flight.
Grounding Statement
Picture the small ball resting between its two marks; that is the cockpit’s simple visual cue that the airplane is balanced side-to-side.
Intuition Check
Centered does not mean the wings are level. It means the airplane is coordinated and not sliding sideways through the air.
Example Sentence 1
As the airplane approached the stall, the pilot used rudder to keep the slip-skid indicator centered and prevent a wing drop.
Example Sentence 2
During a steep turn the pilot added slight rudder pressure until the slip-skid indicator returned to center.