Marker Beacon

Introduction & Background

This topic contains only PANS-AIM requirements relevant for a marker. For general PANS-AIM requirements valid for all kind of Radio navigation aids see topic Navaid [NAV] and subordinated pages.

A marker beacon serves to identify a certain location in space by means of a 75MHz transmitter, which transmits a directional signal to be received by aircraft flying overhead.

There are basically two applications of marker beacons:

• en-route or
• forming part of an ILS system.

In AIXM en-route marker will be coded as Navaid feature. In general, marker forming part of an ILS facility (e.g. outer marker, middle marker) will not be coded as own Navaid feature but as navaidEquipment for the Navaid with type equal-to 'ILS ', 'ILS_DME' or 'LOC', 'LOC_DME' (see also topic Navaid Equipment).

For a marker, PANS-AIM requires some specific properties as part of the minimum AIP data set. These are

identification, name, aerodrome served, hours of operation, ... frequency..., position, ...

In addition, PANS-AIM ENR 4.1 and AD 2.19/AD 3.18 state as requirement

...If the operating authority of the facility is other than the designated governmental agency, the name of the operating authority shall be indicated in the remarks column. Facility coverage shall be indicated in the remarks column.

The diagram below shows the AIXM classes, including the relevant data types, needed to encode that information. The main class is the MarkerBeacon which is a specialisation of the NavaidEquipment.

Marker Beacon Designator & Name

The MarkerBeacon.designator attribute is used to code the identification code given to the navaid.

According to ICAO Annex 10  Chapter 3, the identification of markers part of an ILS should be as follows:

1. Inner marker (IM): dots only,
2. Middle marker (MM): Alternate dot and dash,
3. Outer marker (OM): 2 dashes,
4. Backcourse marker (BCM): shall be clearly distinguishable from the inner, middle and outer marker beacon identification.

En-route Markers and in some States also ILS markers may have alphanumeric designators.

In AIXM 5 the data type for Navaid.designator and also MarkerBeacon.designator viz. CodeNavaidDesignatorBaseType only allows the following pattern ([A-Z]|\d)* and is limited to 4 characters. Hence it can only be used for the designator of en-route markers.

For markers forming part of an ILS facility the MarkerBeacon.auralMorseCode attribute has to be used to code the identifier.

The long name given to the marker is coded using the MarkerBeacon.name attribute.

Also for markers used at aerodrome/heliport (in general as part of an ILS) a name may be encoded, using the corresponding airport/heliport and/or the concerned runway direction. Examples: 'ESNL OM 14', 'OM 09R', 'WEST', etc.

Aerodrome Served

See topic Basic Data for Navaid.

Hours of Operation

See topic Hours of Operation for Navaid.

Marker Frequency

In AIXM 5, the value of the radio emission frequency of the marker is coded by using the MarkerBeacon.frequency attribute.

The corresponding data type contains a uom attribute. For a marker, only the value equal-to 'MHZ' shall be used.

In general, marker beacons operate at 75 MHz.

Minor Axis Bearing

This information is not required by PANS-AIM. ARINC 424defines a" Minor Axis Bearing (MINOR AXIS TRUE BRG)" data field for the "Airport Localizer Marker" records.

in AIXM 5 the MarkerBeacon.axisBearing attribute may be used to indicate the true bearing of the minor axis of marker beacons.

The figure below illustrates how the minor axis is defined for a marker.

Also in some AIPs this information is published.

AIP context

Position

In case a marker beacon collocated with an NDB (Locator) is physically located at the same position as the Locator, the geographic position (latitude and longitude) of the Locator is also the geographic position of the Marker.

In case a Marker is collocated with an NDB (Locator) and the geographic position of the Marker is different from the geographic position of the locator, some restrictions have to be taken into account (see coding rules below).

For more details see topic Navaid Position & Elevation.

Operating Authority

See topic Operating Authority for Navaid.

Facility Coverage

See topic Facility coverage.

Navaid Collocation

In case the marker is used as part of a ILS or Localizer system, the position of it within that system has to be coded.

One or more MarkerBeacon instances may be used as component (NavaidEquipment) for a single Navaid of type 'ILS' or 'ILS_DME' or 'LOC' or 'LOC_DME' instance. However, each MarkerBeacon instance must be related to a maximum of one ILS, i.e. an ILS may have more than one related marker but a marker can only be related to one ILS.

As each marker related to the ILS has to have a different marker position, a maximum of four markers can be part of an ILS/Localizer system, i.e. an Outer, a Middle, an Inner and a Backcourse Marker.

Although not required by PANS-AIM, this information is published in the AIP for ILS/Localizer systems.  Also, the ARINC 424 record type "Airport and Heliport Localizer Marker" contains a data field "Marker Type" (MKR TYPE) for the corresponding information.

In an ILS/Localizer system, a marker may be located basically at 3 different positions: outer, middle and inner. An installation may have a marker at just one, two or all three positions.

Some ILS/Localizer systems provide the possibility to use them backcourse. In such cases, a dedicated marker may be provided to support that kind of operation.

Correspondingly, the data type class for NavaidComponent.markerPosition attribute allows the following values to be coded: 'OUTER', 'MIDDLE,' 'INNER' and 'BACKCOURSE'.

A MarkerBeacon may be collocated with an NDB (Locator).

Usually, the NBD collocated with a marker is a locator (see also topic NDB), whereas the locator in conjunction with the collocated marker is used for ILS approaches.

In the AIP, collocated NDB and marker navaids are sometimes referred to as LOM, LMM or LIM, depending on marker position within the ILS.

There are certain ICAO rules with regard to the relative distance between the marker and the locator. They are mentioned as coding rules.

A marker (and NDB) may only maintain a single collocation relationship at a time, which means that it is not possible to collocate a marker with two different NDBs, and vice versa.

For more details see also topic Landing Systems & Navaid Collocation.

Coding Examples

Coding examples can also be found in the AIP Data Set - Specimen (DONLON):

References