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)
In AIXM, only the aiming point of a TLOF can be coded. Is the aiming point the same 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.
This definitions give the impression that the aiming point is not the centre point of the TLOF. Currently in AIXM, it is not possible to define the two different points for a TLOF. Anyhow, it seems that the relationship hasAimingPoint and the property TLOF.aimingPoint is not correct. It should be rather hasCentrePoint and TLOF.centrePoint. Also, an aiming point may be independent from a TLOF and may also be marked and lighted. It seems that currently aiming point is not covered by AIXM 5. The workaround is to code that information in a Note.
A workaround is to code the centre point of the TLOF using the ElevatedPoint class linked by the hasAimingPoint relationship.
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.
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
As a workaround, the accuracy value for the length and width may be encoded as annotation for the corresponding property.
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 only the extend shall be coded using the corresponding gml element for a circle (see document 12-028_Use_of_GML_for_aviation_data-2.pdf).
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. 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 | TBD | |
| TLA-102 | The TouchDownLiftOff.aimingPoint attribute is mandatory. | Minimum AIP data set | TBD | 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 TLS-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 | Data completeness | TBD | This is not required by PANS-AIM but any TLOF per se has to be located at an Airport/Heliport. |
Coding Examples
Coding examples can be found in the DONLON AIP data set file:
| No. | Description | XPath Expression |
|---|---|---|
| TLA-EX-01 | TLOF (rectangular shape defined by with length/width and extend) | //aixm:TouchDownLiftOffTimeSlice[@gml:id ='TLA_EADH_TLOF'] |