ILS & Localizer Only

For an ILS & Localizer system, PANS-AIM requires some specific properties as part of the minimum AIP data set. These are

... identification, name, ... hours of operation, magnetic variation, frequency..., position, ..., magnetic bearing, true bearing, ...

In addition, PANS-AIM AD 2.19/AD 3.18 require

...type of supported operation for ILS/MLS, ... and for VOR/ILS/MLS also station declination ...used for technical line-up of the aid;

...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 and code lists, needed to encode that information. The main classes are Localizer and Glidepath, which are specialisations of the NavaidEquipment.

Designator & Name

The Localizer will have designator coded.

In general, the Glidepath will not have a value for the designator attribute. If yes, it shall be identical to the designator of the localizer.

In general, neither the Localizer nor the Glidepath will have a name.

Hours of Operation

See topic Hours of Operation for Navaid.

Magnetic Variation

For ILS, PANS-AIM Appendix 1 requires the magnetic variation to be provided. For details about the encoding including rules see the topic Magnetic Variation.

Frequency

The Localizer.frequency attribute is used to code the value of the frequency of the localizer.

The Glidepath.frequency attribute is used to code the value of the frequency of the glidepath.

This can be any decimal value greater than 0. However, there is a coding rule that defines a range of acceptable values.

The corresponding data type ValFrequencyType contains an uom attribute. For both Glidepath and Localizer, only the value equal-to 'MHZ' shall be used.

According to ICAO Annex 10, Volume 1 ^[1]

The localizer shall operate in the band 108 MHz to 111.975 MHz.

The glide path equipment shall operate in the band 328.6 MHz to 335.4 MHz.

Localizer and glidepath frequency will be paired according to ICAO Annex 10, Volume I.

Position

For more details see topic Navaid Position & Elevation.

Localizer Course (bearing)

The magnetic bearing of a Localizer (or Localizer course) is the measured angle between the localizer beam and Magnetic North at the localizer antenna and is coded using the Localizer.magneticBearing attribute. In addition, the Localizer.magneticBearingAccuracy is used to provide the corresponding accuracy value. In general, this information is published on an approach chart.

At some locations of the world, rather a true than a magnetic bearing may be published for the Localizer course. Anyhow, PANS-AIM also requires to code the true bearing, i.e. the measured angle between the localizer beam and True North at the localizer antenna. The Localizer.trueBearing and Localizer.trueBearingAccuracy attributes are used to code that information.

In case either the true or the magnetic bearing is provided, for the other attribute a nilReason should be provided.

Station Declination

The station declination for an ILS is the angular difference between true north and magnetic north at the localizer antenna site at the time the magnetic bearing of the localizer course was established.

It is coded using the Localizer.declination attribute.

Glide Path Angle

For the minimum/conditional AIP data set, the angle of the glide path is actually not required by PANS-AIM (it is only listed in the PANS-AIM Appendix 1). However, in most AIP this information will be published. Also the corresponding ARINC 424 record type for "Airport and Heliport Localizer/Glideslope" contains a "Glideslope Angle (GS Angle)" data field.

The angle of the glide path is coded using the Glidepath.slope and the Glidepath.angleAccuracy attributes.

ICAO Annex 10 defines the ILS glide path angle as follows:

The angle between a straight line which represents the mean of the ILS glide path and the horizontal.

According to ICAO Annex 10 the glide path angle has to be between 1° and 5°.

Normally it is adjusted to an approach angle of 3¿.

RDH

For the minimum/conditional AIP data set, the Reference Datum Height (RDH) is actually not required by PANS-AIM (it is only listed in the PANS-AIM Appendix 1). However, in most AIP this information will be published.

According to ICAO PANS-OPS the RDH is

The height of the extended glide path or a nominal vertical path at the runway threshold.

 The corresponding ARINC 424 record type for "Airport and Heliport Localizer/Glideslope" contains a data field for "Threshold Crossing Height (TCH)" which is defined as

...the TCH value will be the Glideslope Height at the landing threshold for runways with ILS...

The value of the ILS Reference Datum Height (ILS RDH) is coded using the Glidepath.rdh and the Glidepath.rdhAccuracy attributes.

Accoding to ICAO Annex 10, the height of the ILS reference datum for ILS will be 15 m (50 ft). A tolerance of plus 3 m (10 ft) is permitted.

The corresponding data type for the RDH value contains an uom attribute. For a Glidepath, only the value equal-to 'M' (meter) or 'FT' (feet) shall be used.

Type of Supported Operation

According to ICAO Annex 10, Volume I, the lowest authorized ILS minimums, with all required ground and airborne systems components operative, are^:

(a) Category I. Decision Height (DH) 200 feet and Runway Visual Range (RVR) 2,400 feet (with touchdown zone and centre line lighting, RVR 1,800 feet);

(b) Category II. DH 100 feet and RVR 1,200 feet;

(c) Category IIIa. No DH or DH below 100 feet and RVR not less than 700 feet;

(d) Category IIIb. No DH or DH below 50 feet and RVR less than 700 feet but not less than 150 feet; and

(e) Category IIIc. No DH and no RVR limitation.

In AIXM 5, the type of supported operation is coded using the Navaid.signalPerformance attribute. Hence, the signal performance level indicating the precision of an ILS is not encoded for the localizer and glidepath separately, but for the whole ILS or Localizer system.

At some aerodromes, a localizer "back course" is provided. This allows for a non-precision approach in the opposite direction to a front course approach without glide path information.

In case the localizer radiates a usable backcourse signal, the Localizer.backCourseUsable attribute will be encoded with 'YES'.

Operating Authority

See topic Operating Authority for Navaid.

Facility Coverage

See topic Facility coverage.

Served Runway Direction

In AIXM 5, the runway direction for which the localizer/glidepath has been set up is coded using the Navaid.runwayDirection property. The corresponding relationship isInstalledAt indicates that the navaid (i.e. the ILS or Localizer system) is installed at a particular landing area. Hence, not the localizer or glidepath, but the whole ILS system will be related to a particular runway direction.

Navaid Component

ILS/Localizer without DME

According to ICAO Annex 10, Volume I, for an ILS without a collocated DME, there shall be two marker beacons in each installation. A third marker beacon may be added.

The marker beacon system shall be adjusted to provide coverage over the following distances, measured on the ILS glide path and localizer course line:

a) inner marker (where installed): 150 m plus or minus 50 m (500 ft plus or minus 160 ft);

b) middle marker: 300 m plus or minus 100 m (1 000 ft plus or minus 325 ft);

c) outer marker: 600 m plus or minus 200 m (2 000 ft plus or minus 650 ft).

The marker beacons shall operate at 75 MHz with a frequency.

This kind of ILS/Localizer system will be coded as a Navaid.type equal-to 'ILS' or 'LOC' with corresponding NavaidEquipment instances, as a minimum with a Localizer.

In case of Navaid.type equal-to 'ILS', also a Glidepath has to be coded (in case the glidepath of an ILS is inoperable, this will be coded using the NavaidOperationalStatus class, see also topic Hours of Operation for Navaid).

For the range indication one up to three instances of MarkerBeacon will be coded, each of them having a different NavaidComponent.markerPosition value, i.e. 'OUTER', 'MIDDLE', 'INNER', see also topic Marker Beacon.

In case the ILS/Localizer can also be flown backcourse, an additional MarkerBeacon with NavaidComponent.markerPosition equal-to 'BACKCOURSE' will be coded.

In case an NDB forms part of the ILS installation, in general it will be a Locator (i.e. NDB.type equal-to 'L') see also topic NDB.

The NavaidComponent.providesNavigableLocation may be left empty, as in general an ILS will not be used as SignificantPoint for a SegmentPoint for a route or terminal procedure.

For the Localizer, the NavaidComponent.collocationGroup will be  equal-to '1'.

For the Glidepath, the NavaidComponent.collocationGroup will be equal-to '2'.

Each of the MarkerBeacon instances will have another unique sequential number value for the NavaidComponent.collocationGroup attribute, e.g. the outer marker will get the value 3, the middle marker the value 4 and the inner marker if any the value 5.

Each NDB that is collocated with a MarkerBeacon, will get the same number value for the NavaidComponent.collocationGroup attribute as the MarkerBeacon carries.

The Localizer and the NDB shall have a designator. MarkerBeacon are identified by morse code only. The Glidepath may not have a value for the designator.

ILS/Localizer with DME

A DME may be used as an alternative to ILS marker beacons for the range indication. The DME channel may be paired with the localizer frequency.

This kind of ILS/Localizer system will be coded as a Navaid.type equal-to 'ILS_DME' or 'LOC_DME' with corresponding NavaidEquipment instances, as a minimum with a Localizer and a DME.

The designator of the DME will be identical with the one of the Localizer.

In case the DME is collocated with the Glidepath, both will have same number value for the NavaidComponent.collocationGroup.

Coding Rules for ILS/Localizer systems

Coding Examples

TBD in the scope of the DONLON AIXM AIP data set.