What function does the ILS localizer provide and along which axis does it guide the aircraft?

• A. Vertical guidance along the glide path
• B. Lateral guidance along the runway centerline (horizontal axis)
• C. Distance to the threshold
• D. Roll stability and yaw alignment

Answer: (B)

The localizer provides lateral guidance to keep the aircraft centered on the runway centerline, operating in the horizontal plane. It guides the airplane along the runway axis, with the cockpit instruments showing left/right deviation so the pilot or autopilot can steer back to the center. Vertical guidance is handled by the glide slope, not the localizer, which is why the localizer’s role is described as horizontal/lateral guidance along the runway centerline. Distance to the threshold comes from other systems (DME/marker beacons), and roll stability or yaw alignment isn’t the function of the localizer.