How is it indicated that the FMS is in Approach Mode?

The indication that the Flight Management System (FMS) is in Approach Mode is shown by the presence of the green APPR or GPS APPR annunciator on the Primary Flight Display (PFD) at the Final Approach Fix (FAF). This visual cue is critical for pilots as it confirms that the aircraft has transitioned to the approach phase of the flight and is utilizing the appropriate navigational data for guiding the aircraft during its descent toward the runway.

This annunciator provides an immediate and clear indication to the pilot, ensuring they are aware of the current state of the FMS as they prepare for landing. It signifies that the autopilot is engaged in an approach, allowing for a more straightforward flying experience during a critical phase of flight. Recognizing this indicator helps the crew maintain situational awareness and manage the approach efficiently.

Other answer choices, while relevant to overall situational awareness and aircraft operation, do not specifically serve as the primary indication that the FMS is in Approach Mode.