Definition
An older gyroscopic flight instrument that displays the rate at which the aircraft is turning (yaw rate) using a vertical needle, and shows the quality of the turn -- whether it is coordinated, slipping, or skidding -- using an inclinometer ball below the needle.
Plain English
An instrument with two parts: a needle that shows how fast the aircraft is turning, and a ball below it that shows whether the turn is balanced or whether the aircraft is sliding sideways through it.
Context Anchor
Seen in instrument flying when learning how to make and hold controlled turns without relying only on outside visual references.
Derivation
The name describes exactly what it shows: 'turn' (rate of yaw) and 'bank' (whether the aircraft is properly banked for that turn, indicated by the ball staying centred). It is sometimes called the 'needle and ball' for the same reason.
Why Pilots Care
Allows the pilot to maintain coordinated flight and standard-rate turns, which is essential for accurate instrument navigation and preventing loss of control in low visibility.
Intuition Check
Do not assume the word “bank” means this instrument directly shows bank angle. It mainly shows turn rate, while the ball shows whether the airplane is balanced in the turn.
Example Sentence 1
After the attitude indicator failed, the pilot used the turn and bank indicator to keep the wings level and the turn coordinated.
Example Sentence 2
When the ball on the turn and bank indicator stayed centered, the pilot knew the turn was coordinated.