What is indicated when the localizer mode is armed on an approach?

When the localizer mode is armed on an approach, it indicates that the aircraft must maintain its course accuracy within a specified range, which is typically 5 degrees. This means that the aircraft's navigation system is prepared to capture the localizer signal, which provides lateral guidance for aligning the aircraft with the runway centerline during the approach.

The need for accuracy within 5 degrees is critical because, during the approach phase, even minor deviations from the intended course can lead to issues with alignment, potentially impacting the safety and precision of the landing. The localizer helps ensure the aircraft is on the correct lateral path, and being within this accuracy threshold is essential for a successful approach and landing.

Maintaining this level of accuracy helps pilots to effectively manage the approach and prepare for subsequent phases of flight, including glide slope capture and descent. Ensuring the aircraft is properly aligned with the runway before descending aids in a smooth transition into the glide slope, further enhancing flight safety.