Definition
A type of 75 MHz radio marker beacon that transmits a vertical, fan-shaped signal pattern from the ground, used to mark a specific point along an airway or instrument approach. When an aircraft passes overhead, a cockpit marker beacon receiver activates a light and audio tone, confirming the aircraft's position over that fix.
Plain English
A small ground transmitter that beams a signal straight up in a fan shape. When you fly over it, a light flashes and a tone sounds in the cockpit, telling you that you are directly over a known point.
Context Anchor
Seen in older instrument and en route procedure material where a ground-based radio signal is used to identify a reporting point or position along a route.
Derivation
Called a 'fan' marker because the radio signal is shaped like a hand-held fan when viewed from the side: narrow along the airway and wider across it. The shape gives the aircraft a clear, brief overhead indication as it passes through.
Why Pilots Care
It gives pilots precise, positive position confirmation without visual references, supporting accurate timing for altitude, speed, and configuration changes on approach.
Analogy
It is like passing through an invisible gate in the sky. You do not see the gate, but the airplane’s equipment detects it and tells you when you crossed it.
Intuition Check
A fan marker is not a physical sign or flag on the route. It is a radio signal from the ground that marks a location electronically.
Example Sentence 1
Crossing the fan marker, the pilot saw the white marker beacon light flash and heard the tone, confirming the position fix.
Example Sentence 2
Crossing the fan marker, the crew confirmed their position and reported to ATC as required.