What does a turn coordinator indicate?

The turn coordinator is an instrument designed primarily to indicate the rate of turn of the aircraft in degrees per second. When in a coordinated turn, the needle of the turn coordinator shows the rate at which the aircraft is turning. Specifically, a standard rate turn, which is considered to be a turn of 3 degrees per second, will position the needle at a specific mark, allowing pilots to maintain or achieve that standard rate during flight. This information is crucial for pilots to ensure they are turning at a safe and controlled rate, especially in instrument conditions where visual reference to the horizon may be limited.

While the other options relate to various aspects of flight, they do not pertain directly to the function of the turn coordinator. The rate of climb involves vertical speed measurement, heading change rate can be inferred from the turn indicator but is not the direct function of the device itself, and altitude stabilization relates to altitude rather than turns. Therefore, the turn coordinator's primary purpose is to indicate the rate of turn, making this option the most accurate representation of its function.