Which of the following best describes the function of navigation instruments?

Navigation instruments play a crucial role in aviation by providing pilots with the necessary information to maintain a correct heading and follow the planned route. These instruments enable pilots to determine their position relative to navigation waypoints, assist in tracking their flight path, and make any necessary adjustments to ensure they remain on course.

For instance, instruments like the heading indicator and the GPS display provide real-time data on the aircraft's orientation and location, allowing pilots to navigate accurately and efficiently across various flight segments. By relying on this information, pilots can manage their navigation responsibilities effectively, enhancing safety and mission success during flight.

While the other options pertain to important aspects of flying—such as measuring the aircraft's attitude, calculating descent rates, and managing fuel—the central function of navigation instruments is specifically focused on route and heading maintenance.