Which of the following is not a core ILS component?

• A. Localizer
• B. Approach lighting system
• C. Glidepath
• D. RVR

Answer: (D)

The essential ILS components are the signals that guide the aircraft: the localizer provides horizontal alignment with the runway centerline, and the glide slope gives vertical guidance to the correct descent path. An approach lighting system supplements this by helping the pilot see the runway environment in low visibility, but it doesn’t generate or transmit the navigation signals themselves. Runway Visual Range, on the other hand, is a visibility measurement along the approach path used to set landing minimums; it isn’t part of the ILS signal system. So the item that is not a core ILS component is Runway Visual Range.