Introduction
For TLOF, PANS-AIM requires some basic properties as part of the minimum AIP data set. These are
designator, centre point, length, width, surface type.
The diagram below shows the AIXM classes, including the relevant data types, needed to encode that information:
TLOF Designator
The TouchDownLiftOff.designator attribute represents the textual designator of the TLOF, used to distinguish physical TLOFs at an Aerodrome/Heliport that has more than one. The attribute value should reflect the local convention for physical TLOF naming at the Aerodrome/Heliport.
Sample TLOF designator values could be: 'HELIPAD-A', 'HELIPAD-B'; 'TLOF1', 'TLOF2'; etc.
If there is just one TLOF, the designator can be just 'TLOF'.
TLOF Centre Point (aimingPoint)
PANS-AIM requires the centre point of the TLOF to be provided including its elevation and geoid undulation.
AIXM 5.1(.1) issue
The aiming point is not the same position as the centre point of a TLOF. According to ICAO Annex 14, Volume II,
The geographical coordinates of the geometric centre of the TLOF and/or of each threshold of the FATO (where appropriate) shall be measured and reported to the aeronautical information services authority
...
An aiming point marking should be provided at a heliport where it is necessary for a pilot to make an approach to a particular point before proceeding to the TLOF.
The aiming point marking shall be located within the FATO.
The relationship hasAimingPoint and the property TLOF.aimingPoint were incorrectly named in AIXM, as the real intention was to model the TLOF centre point. The aiming point is more appropriately modelled as a RunwayCentrelinePoint, because it is always on a FATO (which in AIXM is modelled as a Runway of type FATO). Therefore, the following workaround is used in AIXM 5.1(.1):
- the TLOF centre point location shall be encoded using the TLOF.aimingPoint;
- in case a true "FATO aiming point" is also provided, this will be coded as a RunwayCentrelinePoint with role equal-to 'OTHER:HEL_AIMING_PT' and associated with the RunwayDirection of the Runway that plays the FATO role for the TLOF.
The ElevatedPoint class provides also dedicated attributes for elevation and geoidUndulation.
In addition the horizontal and vertical accuracy defined by PANS-AIM may be coded using the horizontalAccuracy and verticalAccuracy attribute.
In AIXM 5 the verticalAccuracy refers to both the elevation and the geoidUndulation.
Hence, if the verticalAccuracy is coded for the elevation but the accuracy for the Geoid undulation is not known, this should be put into a corresponding Note.
TLOF Dimension (length & width)
The TLOF dimension attributes are used to describe the physical dimension of a TLOF.
The TouchDownLiftOff.length is the declared longitudinal extent of the TLOF.
The TouchDownLiftOff.width is the declared transversal extent of the TLOF.
PANS-AIM also defines accuracy values for the TLOF length and width.
AIXM 5.1(.1) issue_022/023_TLOF_Length & Width
PANS-AIM defines an accuracy for the TLOF length and width. AIXM 5.1.1 does not have dedicated attributes for that purpose.
Workaround for AXM 5.1(.1): As a workaround, the accuracy value for the length and width may be encoded as annotation for the corresponding property.
Status: see CCB AIXM-269
In addition the extend of the TouchDownLiftOff may be coded using the ElevatedSurface class. In case of a rectangular shape the defined extend (by a set of points with latitude longitude information) shall be consistent with the provided length and width values.
In many cases the shape of a TLOF will be a circle rather than a rectangular. In such case the length and width may not be coded (although required as minimum data for the AIP data set). In such cases the extend shall be coded, using the corresponding gml elements of the Surface class (see also Geometry).
Surface Type (composition)
For the TLOF, PANS-AIM requires to provide the surface type.
In AIXM 5, the SurfaceCharacteristics.composition attribute is used to code the surface type, e.g. asphalt, concrete, grass, etc.
The SurfaceCharacteristics class groups together more attributes that model the characteristics of an airport surface, such as strength, material, etc.
For detailed information about the surface characteristics attributes & corresponding rules please refer to the topic Surface Characteristic [SCH].
Related Airport/Heliport and Runway
Actually, not required by PANS-AIM the TLOF shall be related to an AirportHeliport.
In addition, a TLOF may be situated on a Runway. This association should also be used in order to associate a TLOF with a Runway that is used for final approach by helicopters, while the TLOF itself is located somewhere else on the airport surface. In this regard a runway may be of type Runway or FATO (see also topic Runway [RWY]).
Coding Rules for Basic Data for TLOF
| Identifier | Data Encoding Rule | Justification | Data Verification Rule (UID) | Remarks |
|---|---|---|---|---|
| TLA-101 | The TouchDownLiftOff.designator attribute is mandatory. | Minimum AIP data set | AIXM-5.1_RULE-1A3369 | |
| TLA-102 | The TouchDownLiftOff.aimingPoint property is mandatory. | Minimum AIP data set | AIXM-5.1_RULE-1A338B | The aimingPoint property is used to actually code the centre point, see also AIXM 5.1(.1) issue above. |
| TLA-112 | The TouchDownLiftOff.ElevatedPoint.elevation attribute is mandatory | Minimum AIP data set | TBD | |
| TLA-113 | The TouchDownLiftOff.ElevatedPoint.horizonalAccuracy should be provided. | PANS-AIM | TBD | |
| TLA-114 | The TouchDownLiftOff.ElevatedPoint.verticalAccuracy should be provided. | PANS-AIM | TBD | |
| TLA-115 | The TouchDownLiftOff.ElevatedPoint.geoidUndulation should be provided where appropriate. | PANS-AIM | TBD | |
| TLA-103 | The TouchDownLiftOff.length attribute is mandatory unless an extend is coded. | Minimum AIP data set | TBD | Actually, PANS-AIM requires the length and width as part of the minimum AIP data set. Many TLOF will have rather the shape of a circle. In such cases the length and width attribute do not provide the correct information, but the Surface class shall be used to encode the correct extend of the TLOF. Also, if a a rectangular is encoded as extend for the TLOF the length and width attribute are not needed but may be provided in addition for publication purposes. |
| TLA-104 | The TouchDownLiftOff.width attribute is mandatory unless an extend is coded. | Minimum AIP data set | TBD | see rule TLA-103 |
| TLA-105 | If a value for the TouchDownLiftOff.length attribute is provided a Note for the TouchDownLiftOff with propertyName equal-to 'length' should be coded to provide the corresponding accuracy. | Minimum AIP data set | TBD | |
| TLA-106 | If a value for the TouchDownLiftOff.width attribute is provided a Note for the TouchDownLiftOff with propertyName equal-to 'width' should be coded to provide the corresponding accuracy. | Minimum AIP data set | TBD | |
| TLA-107 | For TouchDownLiftOff the SurfaceCharacteristic.composition attribute is mandatory. | Minimum AIP data set | TBD | |
| TLA-108 | The position given by ElevatedPoint must be plausibly close (less than 20 KM) to that of the ARP of the related AirportHeliport. | EAD | TBD | |
| TLA-109 | ElevatedPoint.geoidUndulation may be specified only if ElevatedPoint.elevation has been specified. | EAD | TBD | |
| TLA-110 | The related Runway should be related to the same AirportHeliport as the TouchDownLiftOff. | EAD | TBD | |
| TLA-111 | If both a width and length and also an extend is coded the data have to be consistent (i.e. the positions defined by the ElevatedSurface have to match with the values of the length and width). | Data consistency | TBD | |
| TLA-116 | The TouchDownLiftOff.associatedAirportHeliport property is mandatory. | AIXM 4.5 / Minimal data rule | AIXM-5.1_RULE-1A334D | This is not required by PANS-AIM but any TLOF per se has to be located at an Airport/Heliport. |
| TLA-117 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.vertical Accuracy shall be 0.5m or less for heliports with or without a PinS approach. | PANS-AIM | AIXM-5.1_RULE-D6D8E (rule does not take into account PinS approach constraint) | The aimingPoint property is used to actually code the centre point, see also AIXM 5.1(.1) issue above. |
| TLA-118 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.vertical Accuracy shall be 0.25m or less for heliports intended to be operated in accordance with ICAO Annex 14, Appendix 2. | PANS-AIM | TBD | |
| TLA-119 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.elevation shall be published with at least 1m or 1ft resolution for heliports with or without a PinS approach or for heliports intended to be operated in accordance with ICAO Annex 14, Appendix 2 (non-precision). | PANS-AIM | AIXM-5.1_RULE-D9C62 Note: the only think that can be verified in this case is the use of either FT or M as unit on measurement. A value such as "200 M" cannot be assumed to break this rule because maybe this is the exact elevation value. | |
| TLA-120 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.elevation shall be published with at least 0.1 m or 0.1 ft resolution for heliports with or without a PinS approach or for heliports intended to be operated in accordance with ICAO Annex 14, Appendix 2 (non-precision). | PANS-AIM | ||
| TLA-121 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.geoidUndulation shall be published with at least 1m or 1ft resolution for heliports with or without a PinS approach or for heliports intended to be operated in accordance with ICAO Annex 14, Appendix 2 (non-precision). | PANS-AIM | AIXM-5.1_RULE-4611A Note: the only think that can be verified in this case is the use of either FT or M as unit on measurement. A value such as "200 M" cannot be assumed to break this rule because maybe this is the exact elevation value. | |
| TLA-122 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.geoidUndulation shall be published with at least 0.1 m or 0.1 ft resolution for heliports with or without a PinS approach or for heliports intended to be operated in accordance with ICAO Annex 14, Appendix 2 (non-precision). | PANS-AIM | ||
| TLA-123 | Coordinates of TouchDownLiftOff.aimingPoint shall be published with at least 6 decimals resolution. | PANS-AIM | PANS-AIM requires a publication resolution of 1/100 sec second, which can be achieved by minimum 6 decimal of a degree. | |
| TLA-124 | If coded, the value of the TouchDownLiftOff.aimingPoint.ElevatedPoint.horizontalAccuracy shall be 1 M or less. | PANS-AIM | AIXM-5.1_RULE-E681, AIXM-5.1_RULE-E682 (2nd rule checks 3.0 FT which is not defined in PANS-AIM) |
Coding Examples
Coding examples can be found in the AIP Data Set - Specimen (DONLON):
| No. | Description | XPath Expression |
|---|---|---|
| TLA-EX-01 | TLOF (rectangular shape defined by with length/width and extend) | //aixm:TouchDownLiftOffTimeSlice[@gml:id ='TLA_EADH_TLOF'] |