Aviation Theory

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 approaches.

From AIM 1-1-9. MARKER BEACON

1. 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.
    
2. 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."
    
1. 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.
1. 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.
2. 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.
    
2. 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.
    
3. 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 antennas.