27 SEP 2021
Additional classes, associations and data types are added in the model representing elements of the Global Navigation Satellite System (GNSS) and their augmentation systems (SBAS/GBAS). Some properties and associations are added or modified in existing AIXM classes, such as RadioFrequencyArea and GuidanceService, in order to support the coding of data related to the new satellite navigation system model.
The current model is lacking the capability to represent the information about satellite navigation systems, augmentation systems and their use for air navigation. Although the list of values for the SpecialNavigationSystem.type attribute includes “GNSS”, the properties of the SpecialNavigationSystem and its associated classes are far from a complete GNSS aeronautical data model for AIS. The current model is also missing the capability to define service coverage and limitations in relation with a runway direction, which may be necessary for certain GBAS configurations.
Therefore, a dedicated set of classes and properties need to be added in the model in order to support the coding of satellite navigation systems information, as relevant for aviation use. The proposed model is based on the ICAO requirements and guidelines for the use of satellite navigation systems, as contained in the ICAO Annex 10, Vol I, 6th Edition and in the ICAO PANS-OPS document. It also takes into consideration the AIS data provision requirements for such systems. The proposed model can be summarised as follows:
The existing RadioFrequencyArea model is used, with some improvements, in order to support the coding of the GBAS service volumes. This requires an additional “zero axis rotation” property in the CircleSector class, in order to indicate that the angles are measured from the runway centreline.
An additional correction concerns the “WAASreliable” attribute of the InstrumentApproachProcedure. Its name was initially derived from the “Wide Area Augmentation System (WAAS)”, which is an FAA-specific implementation of Satellite Based Augmentation System (SBAS). It does not seem to be still necessary, since the SatelliteService class can be used to indicate the local unavailability of an SBAS system.
There is no impact on existing implementations as the current AIXM 5.1.(.1) data remains fully valid against AIXM 5.2. Data providers that might be using SpecialNavigationSystem with type equal-to ‘GNSS’ will have to eventually re-code the information using the new model. No automatic conversion rules are proposed because the current AIXM 5.1(.1) model does not have sufficient GNSS data elements to enable a meaningful mapping.
When receiving data from AIXM 5.2 implementations, current AIXM 5.1(.1) systems will lose most of the data elements introduced in the new AIXM 5.2 model. In order to preserve some minimal information about Procedures that use a satellite navigation system, the backwards mapping rules described further in the document may be applied.
In the UML model, create a new package “Satellite Navigation Systems” under Navaids and Points:
Note: the new CodeSatelliteApproachType data type is defined in AIXM-473 Change Proposal.
The resulting model for Satellite Navigation systems is shown in the following UML class diagram, with the new classes and properties highlighted in blue.
The resulting GBAS model is shown in the following UML class diagram, with the new classes and associations highlighted in blue:
The resulting GuidanceFacility model is shown in the following UML class diagram, with the new classes and associations highlighted (Note: the multiplicity of the GuidanceService class in the association to Procedure is 0..1 on this diagram. This takes into consideration the Change Proposal AIXM-419):
[MAPC-99] No mapping is possible or justified. This is a completely new model for GNSS elements.
[MAPC-02] Applied only for Procedure specialisations that have the new associations for GuidanceService. From the three backward mapping options discussed for this case, the first two (discard the value or use an extension) are straightforward and do not need any further details. The 3rd option (backward mapping into a Note) is detailed in order to provide a complete description of this case and its conversion option:
[MAPC-99] No mapping possible for the rest of the data. The only other option in the previous version is the use of an extension, for those systems that are interested to use the new capability without a complete transition to the new version. Therefore, the following elements shall be removed from the file in order to ensure a valid AIXM 5.1.1 output:
(Note: for mapping test data see:)
|AIXM 5.2||AIXM 5.1(.1)|