Definition
On a turn-and-slip indicator, a trim indication is the condition shown when the ball is centered between the two reference lines, meaning the airplane is in coordinated flight with no slip or skid.
Plain English
The instrument is telling you the airplane is flying straight through the air, not sideways. The ball sitting in the middle is the signal that everything is in balance.
Context Anchor
Seen when using the ball in a turn-and-slip indicator to check whether the airplane is coordinated.
Derivation
Trim' comes from an old nautical sense meaning 'in good order' or 'properly balanced' — a ship was 'in trim' when it sat level in the water. In aviation, the same idea carries over: a trim indication shows the aircraft is balanced in flight.
Why Pilots Care
Correct trim indication confirms coordinated flight, which lowers pilot workload and prevents unintentional slips that can lead to spatial disorientation.
Intuition Check
Trim here does not mean decorative trim or only the elevator trim wheel. Here it means the airplane’s balance as shown by the instrument.
Example Sentence 1
After rolling into the turn, she glanced at the turn-and-slip indicator and saw a clean trim indication with the ball centered.
Example Sentence 2
An out-of-trim condition moved the trim indication ball to one side, prompting immediate rudder correction.