What is the primary function of the turn coordinator in an aircraft?

The turn coordinator's primary function is to show the rate of turn. This instrument provides pilots with a visual indication of how quickly the aircraft is turning and helps maintain the appropriate rate of turn during flight, which is crucial for navigation and aircraft control. A correctly calibrated turn coordinator assists pilots in making precise turns, essential for maneuvering in controlled airspace and executing instrument approaches.

In addition to displaying the rate of turn, the turn coordinator can also indirectly indicate the bank angle, but its primary design and function focus on providing the rate at which the aircraft is turning. Properly monitoring this rate is vital for ensuring that the turn is executed safely and efficiently, preventing excessive banking that could lead to loss of control.

Other choices reflect functions that are not the main purpose of the turn coordinator. While maintaining level flight may involve considering the turn rate, this is not the instrument's primary role. Similarly, measuring altitude changes is unrelated to the turn coordinator, as that is managed by other instruments. While bank angle might be observed, the turn coordinator does not measure it directly, focusing instead on the rate of turn.