Basic Data for TLOF

Table of Content

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:

AIXM 5.2 Improvements

A change proposal (AIXM-561) for the next AIXM 5.2 version has been approved by the AIXM Change Control Board, where the helicopterPerformanceClass attribute is added to AircraftCharacteristics and the association between TouchDownLiftOff and AircraftCharacteristic is established.

The coding guidelines provided here are aligned with forward/backward conversion rules contained in the AIXM-561 Change Proposal.

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 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']