What is the function of the localizer in an ILS approach?

The localizer is an essential component of the Instrument Landing System (ILS), specifically designed to provide lateral guidance to pilots during an approach to an airport. It helps ensure that aircraft are properly aligned with the runway centerline as they descend for landing. By broadcasting a specific radio frequency, the localizer emits a signal that the aircraft's navigation system can detect, enabling the pilot to follow a precise path toward the runway.

This lateral guidance is crucial for maintaining correct flight paths in low visibility conditions, where visual cues may be limited. The localizer facilitates a safe and efficient landing by directing the aircraft to align perfectly with the runway.

In contrast, the other options refer to functionalities that are not associated with the localizer. Vertical guidance is provided by the glide slope, which works alongside the localizer to assist with altitude management during the approach. A missed approach point serves as a predefined location where pilots must initiate a go-around if a safe landing cannot be accomplished, and indicating the runway threshold is not a function of the localizer but is typically marked visually or through other navigational aids.