MLS

Page Table of Content

Introduction & Background

This topic contains only those PANS-AIM requirements relevant for a Microwave Landing System (MLS). For general PANS-AIM requirements valid for all kind of Radio navigation aids see topic Navaid [NAV] and subordinated pages.

ICAO Annex 10, Volume I:

MLS is a precision approach and landing guidance system which provides position information and various ground to air data. The position information is provided in a wide coverage sector and is determined by an azimuth angle measurement, an elevation angle measurement and a range (distance) measurement.

An MLS consists of two main components

Azimuth equipment: An SHF transmitter and associated equipment, radiating signals in a volume of airspace served by the MLS, thereby furnishing azimuth indications to aircraft approaching the runway or back azimuth indications to aircraft departing from the runway or performing a missed approach procedure.
Elevation equipment: SHF transmitter, and associated equipment radiating signals within a volume of airspace served by the MLS, thereby furnishing elevation information as an angular value to aircraft approaching the runway.

The range measurement is provided by a related DME.

For an MLS PANS-AIM requires some specific properties as part of the minimum AIP data set. These are

... identification, name, ... hours of operation, ..., channel..., position, ..., magnetic bearing, true bearing, ...

In addition, PANS-AIM AD2.19/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.

AIP context

The figure below shows an outdated publication of an MLS in an AIP.

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

Designator & Name

The Azimuth will have designator coded.

In general, the Elevation 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 Azimuth nor the Elevation will have a name.

Hours of Operation

See topic Hours of Operation for Navaid.

Azimuth Channel

The Azimuth.channel attribute is used to code indicating the channel on which the Microwave Landing System is operating.

The corresponding data type class CodeMLSChannelType provides a list of values in a range from '500' to '699'.

Position

For more details see topic Navaid Position & Elevation.

Glide Path Angle

For the minimum/conditional AIP data set, the normal glide path angle of an MLS is actually not required by PANS-AIM (it is only listed in the PANS-AIM Appendix 1).

The angle of the glide path is coded using the Elevation.angleNominal and the Elevation.angleAccuracy attributes.

Station Declination

PANS AIM Appendix 1 requires a station declination for an MLS.

AIXM 5.1(.1) issue_031_Azimuth Station declination

In contrary to the VOR and ILS class, for the Azimuth no declination and Zero Bearing Direction attribute is provided. In AIXM 5, this information can only be coded with a Note.

Workaround AIXM 5.1(.1): Code a corresponding Note.

Status AIXM 5.2: To be reported to the CCB

Type of Supported Operation

In AIXM 5, the type of supported operation (e.g. CAT IIIA) is coded using the Navaid.signalPerformance attribute. Hence, the signal performance level indicating the precision of an MLS is not encoded for a particular component, but the whole MLS system.

Note

In AIXM 5, the degree to which navigation aids provide accurate approach guidance for a runway direction will be encoded using the precisionApproachGuidance attribute of the RunwayDirection class. In case data is provided for both attributes, it has to be ensured that it is not contradictory, i.e. the ILS category defined for the runway direction can not be higher than the one of the ILS system serving the runway direction.

In addition, the Azimuth.type attribute may be used to code if the MSL is a 'normal' ('FWD') or 'back' ('BWD') azimuth equipment.

For more information about the coding of an MLS system, see topic Navaid Component & Navaid Colocation.

Operating Authority

See topic Operating Authority for Navaid.

Facility Coverage

See topic Facility coverage.

Served Runway Direction

In AIXM 5, the runway direction the MLS is provided for has to be coded using the Navaid.runwayDirection property. The corresponding relationship isInstalledAt indicates that the navaid (i.e. the MLS system) is installed at a particular landing area. Hence, not a component of the MLS, but the whole MLS system will be related to a particular runway direction. For more information about the coding of an MLS system, see topic Navaid Component & Navaid Colocation.

Coding Examples

As there is hardly any MLS installation in the world remaining, it is not considered necessary to provide an example of an MLS in the scope of the DONLON AIXM AIP data set.