Declared Distances

Introduction

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:

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.

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. The ICAO Annex 14 also defines the threshold as "The beginning of that portion of the runway usable for landing". Therefore, it is recommended to use two different RunwayCentrelinePoint for take-off and respectively landing declared distances, as indicated in the table below. 

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).

	...
				<aixm:RunwayCentrelinePointTimeSlice gml:id="RCP_EADD_27R_START_RUN">
					<!-- ICAO AIP specimen data of DONLON have altered, a displaced THR has been added. The actual THR is used as START_RUN-->
					...
					<aixm:role>START_RUN</aixm:role>
					<aixm:location>
						<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="RCPP2">
							<gml:pos>52.378189 -31.921847</gml:pos>							
							<aixm:horizontalAccuracy uom="M">1</aixm:horizontalAccuracy>
							<aixm:elevation uom="M">16.5</aixm:elevation>
							<aixm:geoidUndulation uom="M">11.5</aixm:geoidUndulation>
							<aixm:verticalAccuracy uom="M">0.25</aixm:verticalAccuracy>
						</aixm:ElevatedPoint>
					</aixm:location>
					<aixm:onRunway xlink:href="urn:uuid:b802d439-e9f3-49f9-96e1-0153b837e113"
						xlink:title="RDN_EADD_27R"/>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd0111">
							<aixm:type>TORA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0111">
									<aixm:distance uom="M">2800</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd0121">
							<aixm:type>TODA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0121">
									<aixm:distance uom="M">2800</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd0131">
							<aixm:type>ASDA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0131">
									<aixm:distance uom="M">2800</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
				</aixm:RunwayCentrelinePointTimeSlice>
	...

Declared Distance related to a Taxiway

Some airports may have declared distances related to a taxiway entry or to the intersection with another runway, when that runway may be used for taxiing. Take-off declared distances can also be provided from a "line-up" position along the runway centerline, which is not directly associated with a runway entry from a taxiway or runway intersection.

In AIXM, 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. In case the declared distances concern a runway intersection, the GuidanceLine can be used to connect two RunwayCentrelinePoint on two different RunwayDirection. The "coming from" point does not mandatory need to be coded with lat/long position, if not known precisely. But it can be used to identify the runway that is used for taxiing.

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'. See also the guidelines concerning start of take-off run positions designation in the Basic Data for Runway Direction (FATO Direction).

			...	
				<aixm:RunwayCentrelinePointTimeSlice gml:id="RCP_EADD_TWY_B">
					<!-- RCP for Declared Distances from TWY B RWY 27R -->
					...
					<aixm:role>START_RUN</aixm:role>
					<aixm:designator>TWY B</aixm:designator>
					<aixm:location xsi:nil="true" nilReason="unknown"/>
					<!-- exact postion of START_RUN is not known -->
					<aixm:onRunway xlink:href="urn:uuid:b802d439-e9f3-49f9-96e1-0153b837e113"
						xlink:title="RDN_EADD_27R"/>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd0112">
							<aixm:type>TORA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0112">
									<aixm:distance uom="M">2200</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd01222">
							<aixm:type>TODA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0122">
									<aixm:distance uom="M">2200</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
					<aixm:associatedDeclaredDistance>
						<aixm:RunwayDeclaredDistance gml:id="rdd0123">
							<aixm:type>ASDA</aixm:type>
							<aixm:declaredValue>
								<aixm:RunwayDeclaredDistanceValue gml:id="rddv0132">
									<aixm:distance uom="M">2200</aixm:distance>
								</aixm:RunwayDeclaredDistanceValue>
							</aixm:declaredValue>
						</aixm:RunwayDeclaredDistance>
					</aixm:associatedDeclaredDistance>
				</aixm:RunwayCentrelinePointTimeSlice>
			...

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.

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 Timesheet may be encoded for the RunwayDeclaredDistanceValue.

AIP Context

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:

Coding Examples

Coding examples can be found in the AIP Data Set - Specimen (DONLON):

References