For Runway Direction, PANS-AIM requires declared distances information as part of the minimum AIP data set. These are
...take off run available (TORA), take-off distance available (TODA), accelerate-stop distance available (ASDA), landing distance available (LDA)
The diagram below shows the AIXM classes, including the relevant data types (in green colour) needed to encode that information:
Conventional distances for a runway direction are maintained by using the RunwayDeclaredDistance class. Conventional distances encompass the following types:
|DeclaredDistance.type||Definition (AIXM 5.1.1 )|
|'TORA'||(Take-Off Run Available):|
The length of the runway declared available and suitable for the ground run of an aeroplane taking off.
|'TODA'||(Take-Off Distance Available):|
The length of the TORA plus the length of the clearway, where provided.
|(Accelerate-Stop Distance Available):|
The length of the TORA plus the length of the stopway, where provided.
|'LDA'||(Landing Distance Available):|
The length of runway which is declared available and suitable for the ground run of an aeroplane landing.
Where a runway has a displaced threshold, the LDA will be reduced by the distance the threshold is displaced, as shown in Figure below.
A displaced threshold affects only the LDA for approaches made to that threshold; all declared distances for operations in the reciprocal direction may be unaffected.
The figure below illustrates the different types of declared distances for runway direction 26R.
A threshold displacement is declared from the physical start of the runway direction. The position of the displaced threshold is encoded as a RunwayCentrelinePoint with the role equal-to 'DISTHR' (see page Basic Data for Runway Direction (FATO Direction)). A runway direction cannot have both a THR and a DTHR, as it would be unclear which one is used for landings.
The actual displacement distance can be coded as RunwayCentrelinePoint.annotation with propertyName='location', purpose='DESCRIPTION'.
The current list of values for declared distance types (CodeDeclaredDistanceType) includes 'DTHR' (thereshold displacement). This is expected to be deprecated in the next AIXM version (raised as issue AIXM-397 in the CCB), because it is incorrect from the ICAO Annex 14 point of view, which has a very precise list of declared distance types and how they are calculated/declared. Also, a THR displacement could also be negative, if the displacement is outbound, which cannot be coded using the 'DTHR' type. Therefore, a simple annotation is proposed to be used for the displacement value.
The coordinates of the displaced threshold are published (RWY 32) and the distance is published.
TODA, TORA, ASDA, LDA
In AIXM 5 the DeclaredDistance.type is used to encode the type of a conventional operational distance declared for a runway direction. The value of the distance declared is coded by using the RunwayDeclaredDistanceValue class. The attributes distance and distanceAccuracy are used for that purpose. According to PANS-AIM, the uom value used for the ValDistanceType for these attributes shall be either 'M' (Meters) or 'FT' (Feet) and no other value.
A declared distance is always related to a RunwayCentrelinePoint, which is the position along the runway centreline from where that distance is calculated. For aircraft performance calculations it is very important to know the exact position from where the declared distance was calculated. While the landing distance (LDA) is normally starting at the THR (or the displaced THR, if applicable), the take-off distances are starting from a centreline alignment point, which may be different from the threshold. Therefore, it is recommended to use two different RunwaCentrelinePoint for take-off and respectively landing declared distances, as indicated in the table below.
|'THR' or 'DISTHR'|
The current instructions from PANS-AIM for the AD 2.13 section is to provide "declared distances to the nearest metre or foot for each direction of each runway". The exact position from where these distances are calculated is in general not indicated, except for additional take-off positions that may exist on a runway, at intersections with taxiways and from additional line-up points. It is common to see TORA, ASDA, LDA declared distances in AIP that are effectively equal to the full physical runway length. In these cases, it can be assumed that the declared distances are in fact associated with a point with role 'START' (the physical start of the runway).
The position (latitude/longitude) of physical start of a runway direction ('START') or the position of the start of the take off run ('START_RUN') may not be known by the organisation publishing the AIP data set
- if the runway direction has a THR and the actual start of run position is not known, then it can be assumed that the THR is also the start run and then it is OK to encode the take-off distances in association with the 'THR'.
- however, if the runway direction has a displaced THR (DTHR), then it is very unlikely that the 'TORA, TODA, ASDA' start from the DTHR position. Most likely they start from a point before the DTHR position. Therefore, in this case, it is proposed to encode a separate 'START_RUN' or 'START' point and associated the 'TORA, TODA, ASDA' with that point, If the exact position is not known, it should be left empty and a nilReason ('unknown') shall be provided. But it is anyhow more correct to encode it like this than to suppose that it starts at the DTHR position.
Declared Distance related to a Taxiway
Some airports may have declared distances related to a Taxiway entry or to a "line-up" position along the runway centerline.
This is supported by the AIXM 5 model. The relationship between the Taxiway and the RunwayDeclaredDistance is established via the GuidanceLine feature.
A corresponding RunwayCentrelinePoint has to be coded for the related taxiway. The role will be 'START_RUN', as such positions are always used as start of the take-off run, not for landing. A RunwayDirection may have more than one RunwayCentrelinePoint of type equal-to 'START_RUN'.
A GuidanceLine will be coded that refers to the Taxiway and the RunwayCentrelinePoint. The GuidanceLine.type which refers will be coded as 'TWY'. The GuidanceLine.designator should be the same as that of the connectedTaxiway.
Start of take-off run positions designation
Many AIP (as in the example shown above) provide a designator for the start of take-off run positions along the runway centerline. In addition, when developing the Digital NOTAM scenarios for declared distance changes, it became clear that such designators would greatly simplify the coding/decoding scenarios. They would allow to identify the point concerned by in the situation where such distances are changes, both when the data is provided by the originator and in the Event/NOTAM text.
Therefore, the RunwayCentrelinePoint.designator is required in for any RunwayCentrelinePoint that has a role different from 'THR' or 'DISTHR' and that has associated DeclaredDistance. For the 'THR'/'DISTHR' it is not important to also have a designator as their role is sufficient to identify them. However, for uniformity sake, they could also be allocated a designator in the form "THR 25R", for example.
Schedule for declared distances
Although not contained in PANS-AIM, the AIXM 5 model also supports the encoding of declared distances that change according to a schedule (e.g. day and night).
For example, the take-off distances at night might be shorter because of noise abatement reasons.
For this purpose a timsheet may be encoded for the RunwayDeclaredDistanceValue.
In some AIP this information is published, see example below.
Declared distances for FATO
Although not required by PANS-AIM for the minimum AIP data set for the FATO subject, AIXM 5 provides dedicated DeclaredDistance.type values for helicopter operations:
|DeclaredDistance.type||Definition (AIXM 5.1.1 )|
|'TODAH'||The length of the FATO plus the length of helicopter clearway (if provided) declared available and suitable for helicopters to complete the take-off.|
|'RTODAH'||The length of the FATO declared available and suitable for helicopters operated in performance class 1 to complete a rejected take-off.|
|'LDAH'||The length of the FATO plus any additional area declared available and suitable for helicopters to complete the landing manoeuvre from a defined height.|
Coding examples can be found in the AIP Data Set - Specimen (DONLON):
//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_09L'] |
The data published in ICAO DOC 8216 for AIP specimen DONLON and in the corresponding eAIP specimen provided by Eurocontrol have been altered in order to have an example for the encoding of a displaced threshold.
//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_27R'] |
//aixm:RunwayCentrelinePointTimeSlice[@gml:id ='RCP_EADD_27R_DISTHR'] |
|//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_09R'] ||
|//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_27L'] ||
|FATO direction||//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_FATO_03'] ||
|FATO direction,||//aixm:RunwayDirectionTimeSlice[@gml:id ='RDN_EADD_FATO_21'] ||
|Start Run for declared Distances from TWY B||//aixm:RunwayCentrelinePointTimeSlice[@gml:id ='RCP_EADD_TWY_B']|
|TWY-EX-01||Taxiway B||//aixm:TaxiwayTimeSlice[@gml:id ='TWY_EADD_B']|
|GLN-Ex-01||Guidanceline for Taxiway B||//aixm:GuidancelineTimeSlice[@gml:id ='GLN_EADD_TWY_B']|