Marker

In instrument flying (or flight IFR), the approach of a Airport and the landing are facilitated by a certain number of electronic systems. Beacons radio called marker are located in the axis of the track, emitting a vertical beam, which makes it possible to check the height of the plane in the phase of end of landing ( short final in the aeronautical language).

There are three markers called respectively Outer Marker (OM), Middle Marker (MM) and Inner Marker (IM).

The overflight of each one of them starts the lighting of indicators on the instrument panel of the aircraft. Each one of them has a specific color corresponding to the one of the beacons.

  • the outer marker, located at approximately 8 km of the threshold, is modulated to 400 Hz, it lights a blue indicator in the cockpit and emits a tonality Morse of 2 features a second (- -).

  • the middle marker, located at approximately 1 km of the threshold, is modulated to 1300 Hz, it lights an orange indicator in the cockpit and emits a Morse tonality of 2 times 1 feature and 1 point (- * - *), but 1 feature and 1 point a second (- *).
  • the inner marker, located at approximately 100 m of the threshold, is modulated to 3000 Hz, it lights a white indicator in the cockpit and emits a Morse tonality of 6 points a second (*** ***). There is no inner marker established on the French aerodromes.

See also Instrument Landing System (THEY)

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