PANS-AIM ENR 4.1 "Radio navigation aids — en-route" and AD 2.19/AD 3.18 "Radio navigation and landing aids" require for the AIP data set the following:
Facility coverage shall be indicated in the remarks column.
ICAO defned coverage as follows
The 'volume' of airspace within which the service is provided and where signal power density is equal to or greater than the specified minimum.
The diagram below shows the AIXM classes, including the relevant data types and code lists, needed to encode that information.
PANS-AIM only requires the facility coverage to be provided as part of the remark. Hence, it is sufficaiant to provide that information as an NavaidEquipment.annotation.
However, AIXM 5 also provides the possibility to code that information in a more accurate form.
The RadioFrequencyArea class is used to code any kind of limitations of a navaid equipments or service frequencies, such as coverage, unusability, etc.
In particular, it may be used to code the coverage of a radio naviagtion or landing aid.
The limitation (coverage) is not related to the Navaid but the NavaidEquipment class, as each navaid equipment a navaid is composed of may have a different limitation.
Even a navaid may have different limitations for different RadioFrequencyArea.singnalType, e,g. for a TACAN the limitation for the 'AZIMUTH' may be different than for the 'DISTANCE'.
A navaid equipment may have different types of limitations.
The code list of the RadioFrequencyArea.type attribute provides the following values in order to define the type of the navaid limitation.
| 'COV' | Actual coverage range (flight checked). Equivalent to Operational Service Volume. |
| 'T_COV' | Theoretical coverage range (not flight checked). Equivalent to Standard Service Volume. |
| 'SCL' | Scalloping. |
| 'RHG' | Roughness (signal roughness experienced). |
| 'UNREL' | Unreliability. |
| 'RES' | Restricted (use is restricted to defined sectors). |
| 'UUS' | Un-usability (use is not permitted in the defined sectors). |
| 'OUT' | Out of tolerance. |
| 'ESV' | Extended Service Volume (Coverage) |
| 'OTHER' | Other |
For coding the facility coverage RadioFrequencyArea.type equal-to 'COV' will be used.
Altough PANS-AIM only requires the facility coverage to be coded also other limitations of a navaid may be provided in the scope of an AIP data set.
Subsequently the CircleSector class is used to code the details of the coverage, i.e. to describe a 3D pattern based on start angle, stop angle, inner distance, outer distance and upper/lower altitude. A coverage may consist of more than one circle sector.
Another possibility would be to define the extent of the coverage using thegml elements related to the Surface class.
For coding the horizonal extend of a sector 7 attributes will be used:
- The CircelSector.fromArc attrbute isused to define the beginning of angle of the sector.
- The CircelSector.toArc attrbute is used to define the ending of angle of the sector.
- The CircelSector.arcDirection attribute is then used to indicate if the direction fromArc to the toArc is clock-wise ('CWA') or counter-clockwise ('CCA').
- The CircleSector.angleDirectionReference attribute is used to define the direction with regard to a reference point, i.e. if the angles have to be read 'FROM' or 'TO' the navaid.
- In addition the CircelSector.type attrbute is used for indicating the type of the angles: magnetic bearing, true bearing, VOR radial, etc.
In order to complete the horizontal extend of the sector a CircleSector.outerDistance has to be defined. In addtion also a CircleSector.innerDistance will be defined. In case the inner distance is at the position of the Navaid it shall be coded equal-to '0'. The UomDistanceType class provides a set of values that can be used for the coding of the two distances.
For the coding of the vertical extend of a sector at 4 attributes may be used:
The CircleSector.upperLimit attribute is used for the uppermost altitude or level that is included in the sector.
The CircleSector.lowerLimit attribute is used fotr the lowermost altitude or level that is included in the sector.
The UomDistanceVerticalType class provides a set of values that can be used for the coding of the two vertical limits.
The two correspdonding ...LimitReference attributes define the reference surface used for the value of vertical limits. For example, Mean Sea Level ('MSL'), Ground ('SFC'), etc.
For more coding details and rules about vertical limits see topic Vertical Limits.
Coding Rules for Facility Coverage
TBD
Coding Examples
The Example below illustrates the encoding of the coverage (DOC) of the VOR Tango (note that the TACAN has other limitations):
The figure below illustrated how the limitations of the VOR Tango look like in regard to the horizontal and vertical limits (drawing is not to scale):
| type | lowerLimit¹ | lowerLimitReference¹ | Upper Limit | upperLimitReference | innerLimit | outerLimit | arcDirection | angleDirectionReference | FromArc | ToArc |
|---|---|---|---|---|---|---|---|---|---|---|
| COV | 0 FT | SFC | 500 FL | STD | 0 NM ** | 80 NM | CWA | FROM | 045 | 135 |
| COV | 0 FT | SFC | 500 FL | STD | 0 NM ** | 60 NM | CWA | FROM | 135 | 045 |
| UUS | 0 FT | SFC | 3200 FT | MSL | 20 NM | not coded | CWA | FROM | 125 | 145 |
| UUS | 0 FT | SFC | 5200 FT | MSL | 30NM | not coded | CWA | FROM | 125 | 145 |
| UUS | 0 FT | SFC | 7200 FT | MSL | 40 NM | not coded | CWA | FROM | 125 | 145 |
¹ As not specified in the source data, the lower limit and its reference may also not be coded.
** As not specified in the source data, the inner limit may also be left blank.
More examples TBD in the scope of the DONLON AIXM AIP data set.