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Introduction

For Route Segment, PANS-AIM requires some basic properties as part of the minimum AIP data set. This is

..., startpointfrom point, endpointto point, track, distance, upper limit, lower limit, MEA, MOCA, ...

The diagram below shows the AIXM classes, including the relevant data types, needed to encode that information:

Start Point & End Point

ICAO defines a route segment as

A portion of a route to be flown usually without an intermediate stop, as defined by two consecutive significant points.

In AIXM 5, the start and the end properties of the RouteSegment class are used to define the "From point", i.e. the first point of the route segment and "To point", i.e. the second point of a route segment.

The EnrouteSegmentPoint class used for that purpose is a specialisation of the SegmentPoint. It provides the reportingATC attribute which is used for the indication of the ATS / MET reporting requirement 'COMPULSORY' or 'ON_REQUEST' for the corresponding point.

The actual start or end point of a RouteSegment is defined via the pointChoice property that allows to select a SignificantPoint. Not all available choices of significant points (e.g. RunwayCentrelinePoint, etc.) will make sense to be used for a route segment point (see also page SignificantPoint [SPN] ).

Mainly DesignatedPoint and Navaid will be the start or end point of a RouteSegment. In a few countries, also the airport reference point of an AirportHeliport may be used for that purpose.

For defining that the point used for the route segment is an RNAV waypoint (see also topic Designated Point (Overview)) the EnrouteSegmentPoint.waypoint attribute will be encoded with 'YES'.

In addition, AIXM 5 provides as an option to encode the extend of the route segment as geometrical element, using the Curve class. This data may be used for charting purposes. The curve will be encoded according to the corresponding GML specification (see topic Geometry (Overview)). It will contain the coordinates of the start and end point of the route segment. It shall be ensured that the data (i.e. coordinates) provided in the Curve element(s) match with those provided as start and end of the RouteSegment.

Implicit direction

As every route segment is defined 'from' a start point 'to' an end point, it has an implicit direction. This direction should be consistent with the direction of the route. The start point of a route should also be the 'from' point of the first route segment and the end point of the route should be the 'to' point of the last segment.

The implicit direction of a route segment is relevant when specifying the route availability (see also page Direction of Cruise Levels).

Rules are included in the model to enforce consistency between the general direction of the route and the implicit direction of every segment (see below).

Track & Length

The RouteSegment class provides several attributes to define the initial trueTrack, initial magneticTrack, the initial reverseTrueTrack and the initial reverseMagneticTrack of it.

For "ENR 3.3 Area navigation routes", PANS-AIM explicitly requires that the magnetic bearing of the route segment is provided. For all other routes defined in ENR 3, PANS-AIM requires a track or VOR radial applying the following note

Bearings, tracks and radials are normally magnetic. In areas of high latitude, where it is determined by the appropriate authority that reference to Magnetic North is impractical, another suitable reference, i.e. True North or Grid North, may be used.

Tracks and reverse tracks if any, shall be encoded taking into account the implicit direction of the route segment, i.e. the defined start and end point, (see also above). In this regard, the tracks are from the start point of the segment, whereas the reverse tracks are from the end point of the route segment.

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From Point & To Point

ICAO defines a route segment as

A portion of a route to be flown usually without an intermediate stop, as defined by two consecutive significant points.

In AIXM 5, the start and the end properties of the RouteSegment class are used to define the "From point", i.e. the first point of the route segment and "To point", i.e. the second point of a route segment.

The EnrouteSegmentPoint class used for that purpose is a specialisation of the SegmentPoint. It provides the reportingATC attribute which is used for the indication of the ATS / MET reporting requirement 'COMPULSORY' or 'ON_REQUEST' for the corresponding point.

The actual start or end point of a RouteSegment is defined via the pointChoice property that allows to select a SignificantPoint. Not all available choices of significant points (e.g. RunwayCentrelinePoint, etc.) will make sense to be used for a route segment point (see also page SignificantPoint [SPN] ).

Mainly DesignatedPoint and Navaid will be the start or end point of a RouteSegment. In a few countries, also the airport reference point of an AirportHeliport may be used for that purpose.

For defining that the point used for the route segment is an RNAV waypoint (see also topic Designated Point (Overview)) the EnrouteSegmentPoint.waypoint attribute will be encoded with 'YES'.

In addition, AIXM 5 provides as an option to encode the extend of the route segment as geometrical element, using the Curve class. This data may be used for charting purposes. The curve will be encoded according to the corresponding GML specification (see topic Geometry (Overview)). It will contain the coordinates of the start and end point of the route segment. It shall be ensured that the data (i.e. coordinates) provided in the Curve element(s) match with those provided as start and end of the RouteSegment.

Implicit direction

As every route segment is defined 'from' a start point 'to' an end point, it has an implicit direction. This direction should be consistent with the direction of the route. The start point of a route should also be the 'from' point of the first route segment and the end point of the route should be the 'to' point of the last segment.

The implicit direction of a route segment is relevant when specifying the route availability (see also page Direction of Cruise Levels).

Rules are included in the model to enforce consistency between the general direction of the route and the implicit direction of every segment (see below).

Track & Length

The RouteSegment class provides several attributes to define the initial trueTrack, initial magneticTrack, the initial reverseTrueTrack and the initial reverseMagneticTrack of it.

For "ENR 3.3 Area navigation routes", PANS-AIM explicitly requires that the magnetic bearing of the route segment is provided. For all other routes defined in ENR 3, PANS-AIM requires a track or VOR radial applying the following note

Bearings, tracks and radials are normally magnetic. In areas of high latitude, where it is determined by the appropriate authority that reference to Magnetic North is impractical, another suitable reference, i.e. True North or Grid North, may be used.

Tracks and reverse tracks if any, shall be encoded taking into account the implicit direction of the route segment, i.e. the defined start and end point, (see also above). In this regard, the tracks are from the start point of the segment, whereas the reverse tracks are from the end point of the route segment.

The length attribute allows to define the distance of the path of the RouteSegment. The length depends on the pathType, which may be a great circle ('GRC'), a rhumbline ('RHL') or a geodesic line ('GDS'). 

PANS-AIM Appendix 1 also defines accuracy values the length. Also for the tracks but only for terminal arrival departure.

Lateral Limits

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Lateral Limits

For "ENR 3.1 Lower ATS routes" and "ENR 3.2 Upper ATS routes", PANS-AIM requires the provision of lateral limits.

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Regarding the general encoding guidelines and rules for vertical limits see topic Vertical Limits.

Level

Although this information is not explicitly required by PANS-AIM it should be coded at least for route segments published in an AIP in Section ENR 3.1 Lower ATS routes and  ENR 3.2 Upper ATS Routes, with 'LOWER' and 'UPPER' respectively.

Coding Rules for Basic Data for Route Segment 

Regarding the general encoding guidelines and rules for vertical limits see topic Vertical Limits.

Level

Although this information is not explicitly required by PANS-AIM it should be coded at least for route segments published in an AIP in Section ENR 3.1 Lower ATS routes and  ENR 3.2 Upper ATS Routes, with 'LOWER' and 'UPPER' respectively. This is also relevant as some Coding Rules relate on this information (see below).

Coding Examples

The figure below gives a simple example of the encoding of the route segment from "DINKI" to "LNO".

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More coding examples can be found in the AIXM DONLON AIP data set AIP Data Set - Specimen (DONLON).

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