Marker Beacon System
The marker beacon system is a radio navigation aid which determines the distance between the aircraft and the runway threshold.
The system provides visual and aural indications of the passage of the aircraft over the marker transmitters located on the ground.
MKR beacon system consists of 3 transmitters on ground
(outer, middle and inner markers) and a receiver at the aircraft.
The three marker transmitters positioned on the ground at known distances from the runway threshold
All marker stations transmit on a basic radio frequency carrier of 75 MHZ. The thing that distinguishes one from the other is the frequency of the audio tone which modulates the carrier frequency (AM modulation).
The Outer Marker transmits 400 HZ tone, and Blue flash.
The Middle Marker transmits 1300 HZ tone and Amber flash.
The Inner Marker transmits 3000 HZ tone. and White flash
When the aircraft passes through the beam of a marker, the modulating frequency is detected.
On most A/Cs there are 2 marker systems with only 1 antenna. One of these systems is active and the other is backup. The active marker is connected to the antenna.
With Poing or Embraer aircraft have more one antenna.
The Marker receiver is combined with the VOR receiver