Definition
A flight instrument that shows two things at once: the rate at which the aircraft is turning (yawing about its vertical axis) and whether the turn is properly coordinated. The turn information comes from a gyroscope mounted so that its spin axis is horizontal and aligned with the aircraft's longitudinal axis; when the aircraft yaws, the gyro precesses and deflects a needle proportional to the rate of turn. The slip information comes from a separate, non-gyroscopic curved glass tube containing a ball in damping fluid; the ball's position shows whether the turn is coordinated, slipping (ball to the inside), or skidding (ball to the outside).
Plain English
An instrument with two parts. A needle tells the pilot how fast the airplane is turning. A ball in a curved tube tells the pilot whether the turn is being flown smoothly with the right amount of rudder.
Context Anchor
Seen on the instrument panel, especially during instrument flying, basic attitude-instrument practice, and checks for coordinated turns.
Derivation
"Turn" refers to the aircraft's change of heading. "Slip" comes from the way an uncoordinated aircraft slides sideways through the air rather than tracking cleanly through the turn — the airplane is literally slipping through the air instead of carving the turn.
Why Pilots Care
Helps the pilot keep turns coordinated, avoiding inefficient flight or loss of control.
Analogy
It is a little like feeling yourself slide sideways in a car during a turn. The pointer tells you that the car is turning; the ball tells you whether the turn feels balanced or whether you are being pushed to the side.
Intuition Check
Do not read “slip” here as a tire slipping on a runway. In this instrument, slip means the airplane is moving partly sideways through the air. Also, the turn pointer does not show bank angle; it shows rate of turn.
Example Sentence 1
When the attitude indicator failed in cloud, the pilot used the turn and slip indicator to hold a standard-rate turn back toward clear air.
Example Sentence 2
In the instrument scan, the turn and slip indicator confirmed the airplane was not slipping through the turn.