Also found in: Acronyms.
fan marker[′fan ‚märk·ər]
A highly directional radio signal transmitted vertically upward from a transmitter located along a navigational radio-range, as in an instrument landing system (ILS). The output of a fan marker is heard only when the aircraft is directly above the transmitter, thus indicating to the pilot his exact position. A fan marker is keyed for identification. Also called a fan-marker beacon.