Definition
A type of radio marker beacon that transmits a vertically directed signal in a fan-shaped pattern, used along certain airways and approach paths to indicate a specific position over the ground. When an aircraft passes over the beacon, a cockpit light illuminates and an audio tone is heard, confirming the aircraft's position.
Plain English
A small ground radio station that sends a signal straight up in a wide, flat shape. When you fly over it, a light blinks and a tone sounds in the cockpit so you know exactly where you are.
Context Anchor
Seen in NOTAMs, older instrument procedure material, chart notes, and discussions of marker beacon equipment.
Derivation
Called a 'fan' marker because the radio signal radiates upward in a flat, fan-shaped pattern rather than a narrow cone. The shape gives the aircraft a wider window to detect the signal as it passes overhead.
Why Pilots Care
Provides reliable position confirmation during an approach when other navigation aids may be limited or unreliable.
Analogy
Think of walking through a thin sheet of mist sprayed upward from the ground. You only notice it as you pass through that sheet; a fan marker works similarly with a radio signal instead of mist.
Intuition Check
Do not read “fan” as a cooling fan. Here, “fan” describes the shape of the radio signal, and “marker” means a radio signal that marks a location.
Example Sentence 1
The instructor pointed to the old chart and explained that the fan marker once provided a position fix along the airway.
Example Sentence 2
The pilot listened for the fan marker signal while cross-checking the approach plate.