This is an area where aircraft circle to land under visual conditions after completing an instrument landing approach. The model provides two possibilities for coding the elements of a circling procedure:
- using an ApproachCondition with finalApproachPath equal-to 'CIRCLING' associated with the FinalLeg of an InstrumentApproachProcedure, including Minima and any eventual CirclingRestriction
- using a CirclingArea as starting point and eventually associating it with an InstrumentApproachProcedure, if applicable.
The following diagram highlights the classes and associations that are used in both approaches.
The association CirclingArea has ApproachCondition allows coding the combination of obstacle clearance or decision altitude/heights with the aircraft categories to which they apply. This is done through the associations indicates Minima and isApprovedFor AircraftCharacteristics respectively. The details of the Minima class are explained in the Final approach minima section.
Circling restrictions may be provided as text and eventually with a graphic depiction. The text may coded as a Note with purpose equal-to 'DESCRIPTION' (and no propertyName) associated with the CirclingRestriction. The conventional graphical representation of the circling restrictions, as appearing on approach charts, may be coded with the Surface object. The radius, size and other graphical elements of that depiction are at the discretion of the data provider, as they typically not to scale.
The model also has an association CirclingRestriction isDescribeBy CircleSector. However, there is no clear need for this association as no example of such circling sector restrictions could be found. In addition, the center point of the sector is not specified by the model, which makes this association unusable.