fan-marker beacon[′fan ‚märk·ər ‚bē·kən]
A very-high frequency radio facility having a vertically directed fan beam interesecting an airway to provide a fix. Also known as fan marker; radio fan-marker beacon.
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.