What is a Marker Beacon and its place in ILS?

• A. Rotating beacon at the runway threshold.
• B. Fixed-distance beacons along the approach: Outer Marker, Middle Marker, and Inner Marker.
• C. A type of satellite navigation used for en route.
• D. A ground-based wind measurement device.

Answer: (B)

Marker beacons are ground-based beacons placed along the ILS approach path to give pilots fixed distance cues on the approach. They are fixed-distance beacons along the approach: Outer Marker, Middle Marker, and Inner Marker. Each beacon transmits on a 75 MHz signal and provides distinct cockpit cues—typically lights of different colors and audible tones—that tell you where you are along the glide path. The Outer Marker is farthest from the runway, the Middle Marker is closer in, and the Inner Marker sits very near the threshold and is used mainly for Cat II/III approaches. This setup helps confirm you’re following the published approach and gauge remaining distance and height. The other options describe different runway lighting, satellite navigation, or wind-measurement devices, none of which are marker beacons.