The explanation of marker beacons given in the AIM is fairly complete.
For that reason, they will not be covered in any more detail until
we get to the lessons on actually using the marker beacons for instrument
From AIM 1-1-9. MARKER BEACON
- Marker beacons serve to identify a particular location
in space along an airway or on the approach to an instrument runway.
This is done by means of a 75 MHz transmitter which transmits
a directional signal to be received by aircraft flying overhead.
These markers are generally used in conjunction with enroute NAVAIDs
and ILS as point designators.
- There are three classes of enroute marker beacons: Fan Marker
(FM), Low Powered Fan Markers (LFM) and Z Markers.
They transmit the letter "R" (dot dash dot) identification, or
(if additional markers are in the same area) the letter "K," "P,"
"X," or "Z."
- Class FMs are used to provide a positive identification of
positions at definite points along the airways. The transmitters
have a power output of approximately 100 watts. Two types of
antenna array are used with class FMs.
- The first type used, and generally referred to as the standard
type, produces an elliptical shaped pattern, which, at an
elevation of 1,000 feet above the station, is about 4 NM wide
and 12 NM long. At 10,000 feet the pattern widens to about
12 NM wide and 35 NM long.
- The second array produces a dumbbell or boneshaped pattern,
which, at the "handle", is about three miles wide at 1,000
feet. The boneshaped marker is preferred at approach control
locations where "timed" approaches are used.
- The class LFM or low powered FMs have a rated power output
of 5 watts. The antenna array produces a circular pattern which
appears elongated at right angles to the airway due to the directional
characteristics of the aircraft receiving antenna.
- The Station Location, or Z-Marker, was developed to meet the
need for a positive position indicator for aircraft operating
under instrument flight conditions to alert pilots when passing
directly over a low frequency navigational aid. The marker consists
of a 5 watt transmitter and a directional antenna array which
is located on the range plot between the towers or the loop