Start Point & End Point
Route Segment 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 theairport 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 addtion 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 has to 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 & Lenght
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, have to 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 considered to be from the start point of the segment whereas the reverse tracks are considred to be to from the end point of the route segment.
Open Question RSG_1-1
AIXM 5.1.1 does not provdie the possibility to define if the path between on the route segment is a VOR radial. Shall 'OTHER:VOR_RADIAL' for RouteSegment.pathType be used for that purpose.
The length attribute allows to define the length of the path of the RouteSegment. The length actually depends on the pathType, which may be a great circle ('GRC'), a rhumbline ('RHL') or a geodesic line ('GDS').
According to PANS-AIM an the length of a route segment shall be provided as geodesic distance.
Lateral Limits
For "ENR 3.1 Lower ATS routes" and "ENR 3.2 Upper ATS routes", PANS-AIM requires the provison of lateral limits.
The RouteSegment class provides the attributes widthLeft and widthRight to define the lateral limits. These are the distances from the centreline of the route segment to the left and right edge respectivley. For example, if the route segment has a defined width of 10 NM for each of the attributes will carry the value '5' uom equal-to 'NM'.
Vertical Limits
PANS-AIM requires that all routes/route segments have at least a lower limit and an upper limit.
For some types of routes, viz. ENR 3.1 (Lower ATS Routes) and ENR 3.4 (Helicopter Routes), also minimum obstacle clearance altitudes and minimum flight altitudes, respectively shall be provided.
According to ICAO Annex 11:
The minimum flight altitudes determined shall provide a minimum clearance above the controlling obstacle located within the areas concerned.
Whereas, the States should publish, “The criteria used to determine minimum flight altitudes”, in AIP section GEN 3.3.5.
Depending on the purpose and classification of the route different vertical limits may be required by PANS-AIM:
ENR 3.1 (Lower ATS Routes):
upper and lower limits or minimum en-route altitudes.
Since en-route flights at or above the lowest usable flight level are flown at flight levels, it is suggested that these limits be expressed in flight levels (FL) whenever such flight levels are not likely to fall below the lowest safe altitude; otherwise, they should be expressed in altitude.
ENR 3.2 (Upper ATS Routes):
upper and lower limits (usually in flight levels "FL”).
ENR 3.3 (RNAV Routes):
upper and lower limits (usually in flight levels "FL”).
ENR 3.4 (Helicopter Routes):
upper and lower limits; minimum flight altitudes
ENR 3.5 (Other Routes):
No requirements stated regarding vertical limits.
The following table gives an overview which vertical limits are required by PANS-AIM for the AIP data set and the corresponding AIXM attributes of the RouteSegment class (Note 1) :
| PANS-AIM | AIXM 5.1.1 | Remarks | |||
|---|---|---|---|---|---|
| Property | Definition/Desription | Relevance | Attribute | Description | |
| Upper limit | The upper limit of the route segment | ENR 3.1-3.4 | upperLimit | The vertical position of the route segment ceiling. | |
| Lower Limit | The lower limit of the route segment | ENR 3.1-3.4 (Note 2) | lowerLimit | The vertical position of the route segment floor. | Note 2 According to PANS-AIM for ENR 3.1 Lower ATS Route,
shall be defined. In the "old" ICAO Annex 15 it was
|
| Minimum obstacle clearance altitude (MOCA) | The minimum altitude for a defined segment of flight that provides the required obstacle clearance. minimumObstacleClearingAltitude | ENR 3.1 Lower ATS Route | minimumObstacleClearanceAltitude | Minimum obstacle clearance altitude (MOCA). The minimum altitude for a defined segment of flight that provides the required obstacle clearance. | According to PANS-OPS
In PANS-AIM it is only required for ENR 3.1Lower ATS Routes. The MOC value to be applied in the primary area for the en-route phase of an IFR flight is 300 m (1 000 ft) as a minimum. |
| Minimum en-route altitude (MEA) | The altitude for an en-route segment that provides adequate reception of relevant navigation facilities and ATS communications, complies with the airspace structure and provides the required obstacle clearance. | ENR 3.1 Lower ATS Route (Note 2) | minimumEnrouteAltitude | Minimum en-route altitude (MEA). The altitude for an en-route segment that provides adequate reception of relevant navigation facilities and ATS communications, complies with the airspace structure and provides the required obstacle clearance. | According to PANS-OPS
|
| Minimum flight altitude | Minimum flight altitude | ENR 3.4 Helicopter routes | ??? | According to PANS-AIM
In PANS-AIM the term is only used for "ENR 3.4 Helicopter routes" ICAO ANnex 11, 2.22 Minimum flight altitudes
Open Question RSG_1-2 Isn't acc. to Annex 11 the MOCA and the Minimum flight altitude for Routes ? Or is both the MEA and the MOCA considered as a kind of minimum flight altitude (see also change for ENR 3.1. Lower ATS routes? | |
| NA | NA | NA | minimumCrossingAtEnd | The lowermost vertical position at the end point, when flying on the route portion in the direction indicated in the RoutePortionUsage. | AIXM 5.1.1 issue RoutePortionUsage is not defined in AIXM 5.1.1. If this attribute is related to the route portion, whay is it part of the RouteSegment class? |
| NA | NA | NA | maximumCrossingAtEnd | The uppermost vertical position at the end point, when flying on the route portion in the direction indicated in the RoutePortionUsage. | Same issue as above. |
Note 1
Open Question RSG_1-3
In some State AIPs, an additional limit, "overriding" the Lower limit specification is published. To publish this minimum limit, often statements such as " but at least" are used. The Lower limit override always refers to ground e.g. "feet above ground".
How to encode this in AIXM 5.1.1? in AIXM 4.5 a dedicated attribute was provided VAL_DIST_VER_LOWER_OVRDE
Example:
Regarding the general encoding guidelines and rules for vertical limits see topic Vertical Limits [VER].
Coding Rules for Basic Data for Route Segment
| Identifier | Data Encoding Rule | Justification | Data Verification Rule (UID) | Remarks |
|---|---|---|---|---|
| RSG-101 | The RouteSegment.navigationType attribute is mandatory. | Note To be clarified how PBN specification will be encoded. | ||
| If VAL_DIST_VER_UPPER is specified, then UOM_DIST_VER_UPPER and CODE_DIST_VER_UPPER are mandatory. | ||||
| If the unit of measurement has the value 'FL' or 'SM', then the attribute CODE_DIST_VER_UPPER must have the value 'STD' (standard pressure). | ||||
| If VAL_DIST_VER_LOWER is specified, then UOM_DIST_VER_LOWER and CODE_DIST_VER_LOWER are mandatory. | ||||
| When translated to use the same unit of measurement and the same vertical reference, VAL_DIST_VER_LOWER must be lower than or equal to VAL_DIST_VER_UPPER. | ||||
| If the unit of measurement has the value 'FL' or 'SM', then the attribute CODE_DIST_VER_LOWER must have the value 'STD' (standard pressure). | ||||
| RSG-201 | Two consecutive route segments (of the same Route) should have vertical limits that, if not overlapping, should not be further away than 1000 FT. For example, if segment 1 is FL245 to FL295 and segment 2 is FL310 to FL490, (this rule will need to be adjusted based on operational experience).
| EAD Rule | TBD | |
| RSG-202 | The angle between two consecutive segments of the same route cannot exceed 90 degrees.
| EAD Rule | TBD | |
| RSG-203 | At the border (defined as a buffer area of 2 km on each side) between two areas of responsibility, route segments should be continued by route segments of the same or another Route. | EAD Rule | TBD | Open Question RSG_1-4 This rule is based on the areas of responsibility defined in EAD. Shall there be a similar rules for the AIP data set based e.g.on FIR/UIR? |
| RSG-204 | Route segments of the same Route should be consecutive (no gaps): not more than two significant points should be either the start or the end of a single route segment. | EAD Rule | TBD |
According to the rule definition the rule is violated, because four significant points "KPT", "TGO", "KRH" and "ECCHO" are used only once, either as start or end point of a route segment. |
| RSG-205 | Route segments of the same Route should be consecutive: no segment should be described in the opposite order of significant points (start instead of end and vice-versa) compared to the adjacent segments. | EAD Rule | TBD |
In the given example the rule is violated, because route segment "ECCHO - ANEKI" is described in the opposite order of the adjacent segments. |
| RSG-206 | Route segments of the same Route should be consecutive (no multiple branches): no significant point should appears on 3 or more segments, either as start or as end point. | EAD Rule | TBD |
According to the rule definition the rule is violated, because ANEKI appears on three route segments. Subsequently this results in multiple branches; "ANEKI - ECCHO" and ANEKI - RUDUS". |
| RSG-207 | The position of the SignificantPoint used as the beginning of the RouteSegment must be separated by at least 30m (1 sec of arc) from the position of the SignificantPoint used as the end of the RouteSegment.
| EAD Rule | TBD | |
| RSG-208 | widthLeft and widthRight must have a value between 0.5 NM and 10 NM. | EAD Rule | TBD | Open Question RSG_1-5 Is this rule justified by an ICAO doc? |
| RSG-209 | The value of EnRouteSegmentPoint.reportingATC for RouteSegment.start and RouteSegment.end of any two consecutive segments of the same route must be consistent. | EAD Rule | TBD | In case of FIR BRDY points there are situations when the source data of the concerned neighbouring countries do not match. For example on routes crossing the border between Latvia and Sweden, the report at the border points is specified 'on request' in the Sweden AIP and as 'compulsory' in the Latvia AIP. |
| RSG-210 | The difference between length and the calculated length of the related RouteSegment cannot exceed 5 KM.
| EAD Rule | TBD | Open Question RSG 1-6 PANS-AIM requires an accuarry of 1/10 KM. Shall the rule be accordingly? |
| RSG-211 | The difference between Initial trueTrack and the calculated initial true track of the related RouteSegment cannot exceed 2 degrees. The difference between reverseTrueTrack and the calculated reverse initial true track of the related RouteSegment cannot exceed 2 degrees.
| EAD Rule | TBD |
Coding Examples
The figure below gives a simple example of the encoding of the route segment from "DINKI" to "LNO".
The figures below gives an example of the encdoing of the route segment (from "BARIM" to "WOB") including the mapping from AIXM UML to AIXM XML.
More examples TBD in the scope of the DONLON AIP data set XML.