What does a turn coordinator indicate?

The turn coordinator primarily indicates the movement of the aircraft about the yaw and roll axes. This instrument is designed to show the rate of turn and is particularly useful in determining if the aircraft is in a coordinated turn or if it is skidding or slipping. The device displays this information through a visual representation, typically a miniature airplane symbol or a ball in a curved glass tube.

When an aircraft is in a well-coordinated turn, the ball will remain centered. If the aircraft is skidding (too much rudder for the angle of bank), the ball will move in the direction of the turn. If the aircraft is slipping (not enough rudder), the ball will move in the opposite direction. The turn coordinator thus provides crucial information about how the aircraft is rotating along its axes during flight, allowing pilots to maintain coordinated flight and ensure safe handling characteristics.

In contrast, the other options do not pertain to the primary functions of a turn coordinator. The pitch axis is related to climb or descent, altitude changes don’t pertain to turn dynamics, and while bank angle is relevant, it is not the direct indication of a turn coordinator, which focuses on the relationship between yaw and roll.