Which mode should be selected to fly the flight management system route?

The correct choice is to select the NAV mode to fly the flight management system (FMS) route. In aviation, particularly in the context of the A320, the NAV mode is specifically designed to follow the lateral flight path that the FMS has calculated for the aircraft’s route. By engaging NAV, the autopilot system utilizes waypoints and airways programmed into the FMS, ensuring that the aircraft adheres to the planned trajectory efficiently and accurately.

Choosing NAV mode allows the aircraft to automatically navigate to the designated waypoints, making it essential for maintaining the intended course throughout the flight. This is critical for both flight efficiency and safety, as it helps the crew manage navigation tasks effectively without constant manual input.

The other options are not suitable for following the flight management system route. While HDG mode allows the pilot to fly a specific heading, it does not utilize the FMS route or waypoints. GPS may suggest a route but isn’t a dedicated mode in the context of the A320's FMS. LOC refers to the localizer mode used for ILS approaches and does not pertain to general navigation during en route flying. Thus, selecting NAV mode is the most effective way to ensure the aircraft follows the computed route from the FMS