What system allows pilots to locate the runway centerline by providing on-course signals?

The localizer is a critical component of the Instrument Landing System (ILS) that assists pilots in accurately locating the runway centerline. It provides lateral guidance by transmitting a directional signal along the centerline of the runway. This allows pilots to align the aircraft with the runway during the final approach, ensuring they are on the correct path to land.

When a pilot receives this signal, they can determine whether they are on course or if they need to adjust their heading to maintain alignment with the runway. The localizer helps improve landing precision, particularly in low-visibility conditions, contributing to safer flight operations.

In contrast, the marker beacon serves to indicate specific locations along the approach path and does not provide directional guidance. The glideslope, while also part of the ILS, offers vertical guidance rather than lateral alignment. VHF navigation refers to the frequency used for various types of navigation signals, including those from the localizer, but does not specifically denote the guidance system for runway alignment. Thus, the localizer is the correct answer in this context, as it directly relates to identifying the runway centerline.