What is the primary function of a turn coordinator in flight?

The primary function of a turn coordinator is to indicate the rate of turn of the aircraft. This instrument provides critical information to pilots about how quickly the aircraft is turning, measured in degrees per second. By displaying the rate of turn, it helps ensure that the pilot can execute turns at a safe and controlled rate, thereby aiding in effective aircraft maneuvering and stability. It is essential for maintaining the aircraft's balance and coordination during turns, giving pilots the ability to make precise adjustments to their flight path.

Other options may appear related but do not define the core role of the turn coordinator. Maintaining level flight pertains more to pitch control rather than turn coordination. While the instrument can assist with coordination in terms of bank angle, its primary function does not directly measure the bank angle itself. Vertical speed is a separate aspect of altitude management, which the turn coordinator does not address.