Basic Data for En-route Holding

Introduction

Based on PANS-AIM "ENR 3.6 En-route Holding", the following information is considered conditional data for the AIP data set:

1) holding identification (if any) and holding fix (navigation aid) or waypoint with geographical coordinates in degrees, minutes and seconds;

2) inbound track;

3) direction of the procedure turn;

4) maximum indicated airspeed;

5) minimum and maximum holding level;

6) time/distance outbound.

The diagrams below show the AIXM classes, including the relevant data types and code lists, needed to encode that information:

Holding Type

The HoldingPattern.type attribute is used to indicate the type of holding, i.e. if it is an en-route holding ('ENR') or terminal area holding ('TER').

Holdings published in ENR 3.6 should be encoded with type equal-to 'ENR'.

This information is relevant also for ARINC 424, which, within the Holding Pattern Records (EP), distinguishes between

• Enroute Holding Patterns recommended by the official government authority for inclusion on enroute aeronautical charts and
• Terminal Holding Patterns recommended for aeronautical charts for the geographical area of an airport or heliport.

In ARINC 424 the type, Enroute or Terminal, is actually be determined by the type of fix upon which the holding is predicated.

Holding Identification / Fix / Waypoint

PANS-AIM uses the term holding fix (navigation aid) or waypoint. In AIXM the term holding point is used in order to identify the point the holding occurs.

The HoldingPattern.holdingPoint is based on a SegmentPoint. The SegmentPoint may be an EnrouteSegmentPoint or a TerminalSegmentPoint. The SegmentPoint is located at a pointChoice of a SignificantPoint (for more details see topic SignificantPoint (Overview)). In general, this will be either a Navaid or a DesigantedPoint. In certain cases the holding point may be coded as just a Point.

In case a navaid or designated point is used as holding point, its actual geographical location is defined by the referenced instance of the Navaid or DesignatedPoint.

In case the Point class is used to code the holding point, its position (latitude/longitude) will be coded within the HoldingPattern record (i.e. the holding point will not be a separate feature and hence cannot be referenced by other features).

More than one HoldingPattern may be coded using the same holdingPoint, e.g. with different inbound course 090 deg and 135 deg or different turn direction, speed and altitudes, etc.

AIXM 5 does not have a dedicated attribute for the identification of a holding pattern. The identifier of a holding will be derived from the designator of the SignificantPoint used as HoldingPattern.holdingPoint. This means that actually the identifier of the holding will be the designator of a DesignatedPoint or of a Navaid. In a case the holding point is defined by the Point class the holding pattern identifier cannot be derived from any designator.

In case a point reference shall be encoded for the holding point (i.e. an angular and distance indication) the facilityMakeup property of the SegmentPoint has to be used (for point reference details see topic Formation (Angle & Distance Indication)).

Inbound Track

To code the radial, course or bearing of the inbound leg, as it pertains to a holding pattern, the HoldingPattern.inboundCourse attribute is used.

PANS-AIM does not require to code the outbound course. However, AIXM 5 provides the possibility to code the outboundCourse with a corresponding outboundCourseType.

Turn Direction

The HoldingPattern.turnDirection attribute is an indicator of the turn direction ('LEFT', 'RIGHT' or 'EITHER') in an aerial manoeuvre performed by aircraft during holding operations.

In ARINC 424 the Turn (TURN) field of the Holding Pattern record, will always contain either L or R. Hence, a corresponding rule is defined in this guidelines to avoid the value 'EITHER' (see below).

Speed Limit

Maximum holding speeds may be established to keep an aircraft within the protected holding area.

The HoldingPattern.speedLimit attribute is used to code the speed limit imposed on the execution of the holding pattern.

ICAO Doc 8168 PANS-OPS  defines default values for speed limits on holding patterns depending on the altitude it is flown.

Minimum and Maximum Holding Level

The HoldingPattern.upperLimit attribute is used to code the maximum vertical distance (measured from a specified reference) allowed for all aircraft categories, at all defined speeds, operating in a holding pattern.

The HoldingPattern.upperLimitReference attribute is determining the reference surface (Mean Sea Level, Ground, standard pressure, etc.) used for determining the value of the upper limit of a holding pattern.

The HoldingPattern.lowerLimit attribute is used to code the minimum vertical distance (measured from a specified reference) allowed for all aircraft categories, at all defined speeds, operating in a holding pattern.

The HoldingPattern.lowerLimitReference attribute is determining the reference surface (Mean Sea Level, Ground, standard pressure, etc.) used for determining the value of the lower limit of a holding pattern.

For more details about coding vertical limits refer to Vertical Limits.

Time/Distance Outbound

The span of the holding pattern (length of the outbound) may be coded as a choice of the HoldingPatternLength class, either as duration, length, or outbound to a significant point.

In ARINC 424 the field Leg Inbound/Outbound Indicator is used to identify the Leg Length or Leg Time field values as being applicable to either the inbound or the outbound leg of a holding pattern. ARINC 424 does not foresee the coding of a significant point as limitation for the outbound leg.

In case the HoldingPattern outbound leg is defined by an endTime, the HoldingPatternDuration.duration attribute is used to define the duration of the holding pattern outbound leg.

In case the HoldingPattern outbound leg is defined by an endDistance, the HoldingPatternDistance.length attribute is used to define the length of the holding pattern outbound leg.

In case the HoldingPattern outbound leg is defined by an endPoint, the SegmentPoint class is used to identify the second waypoint of a two point holding, used to define the end of the outbound leg. The second point may be a choice of SignificantPoint ( for more details see topic SignificantPoint (Overview)).

PANS-OPS states: "Where DME is available, the length of the outbound leg may be specified in terms of distance instead of time."

In case a DME distance defines the end of the outbound leg of the Holding Pattern, the PointReference class referenced by the corresponding SegmentPoint should be used. Actually, there will be no "Point" defined by coordinates coded but just a reference to a navaid.

The DME distance will be encoded as DistanceIndication.distance from the Navaid that is composed of the DME providing the limiting outbound distance.

Also the AngleIndication may be coded, if available or needed.

In the example below, the outbound length of the holding pattern is defined by a DME distance of 15NM from the VOR/DME "BAN". (In this particular example also the holding point itself has a defined point reference, RDL-029 and DME 10,  from the VOR/DME.

Coding Examples

Coding examples can be found in the DONLON AIXM 5.1.1 AIP data set file.

References