The ILS ______ provides course guidance to the runway centerline.

The localizer is a critical component of the Instrument Landing System (ILS) that directs pilots toward the centerline of the runway. It emits a lateral signal to help ensure that the aircraft is aligned correctly as it approaches for landing. The localizer's signal allows pilots to accurately navigate to the runway, providing the necessary course guidance during the final stages of approach.

In contrast, the glideslope provides vertical guidance to ensure that the aircraft descends at the correct angle towards the runway. The marker beacon serves as a point of reference along the approach path, indicating the proximity to the runway, while the transponder primarily transmits information about the aircraft's location and identity to air traffic control rather than providing guidance for landing. Understanding the roles of each of these components is essential for effective use of approach systems in aviation.