Definition
A gyroscopic flight instrument that displays the rate at which the aircraft is turning (yaw rate) using a vertical needle, paired with an inclinometer below it (a curved glass tube containing a ball in fluid) that shows whether the turn is coordinated. The needle indicates how fast the aircraft is turning left or right; the ball indicates whether the aircraft is slipping or skidding sideways through the turn.
Plain English
An instrument with two parts. The top part has a needle that shows how quickly the aircraft is turning. The bottom part has a small ball in a curved tube that shows whether the turn is smooth and balanced or whether the aircraft is sliding sideways.
Context Anchor
Seen on the instrument panel, especially in instrument training and in aircraft equipped with a turn needle and ball instead of a newer turn coordinator.
Derivation
The name describes exactly what the instrument shows: the rate of turn (needle) and any slip or skid (ball). 'Slip' here is the older aviation term for uncoordinated flight, where the aircraft moves sideways through the air rather than tracking cleanly through the turn.
Why Pilots Care
Allows the pilot to maintain coordinated turns, avoiding altitude loss, increased drag, or disorientation.
Intuition Check
A slip here does not mean the airplane is simply losing altitude or losing traction. It means the airplane is moving somewhat sideways through the air during the turn.
Example Sentence 1
After losing the attitude indicator in cloud, the pilot used the turn-and-slip indicator to hold a steady standard-rate turn back toward clear air.
Example Sentence 2
When the inclinometer ball moved left in the turn-and-slip indicators, the pilot added right rudder to center it.