What is the Localizer's function?

• A. To illuminate the runway edge lights.
• B. To align the aircraft with the runway centerline.
• C. To provide vertical descent path guidance.
• D. To identify the runway threshold.

Answer: (B)

The Localizer provides horizontal guidance to align the aircraft with the runway centerline. It transmits signals from a ground antenna at the far end of the runway, creating a course that the airplane’s navigation system can follow to stay centered on the runway path. The cockpit display shows whether you’re left or right of that centerline, so you can intercept and fly the aircraft along the centerline as you approach and descend. Vertical guidance comes from the glideslope, which tells you how steeply to descend, so the localizer is solely about staying on the left–right path along the runway. Threshold identification and other cues are separate from the localizer, which is why its primary job is keeping you aligned laterally with the runway.