The final segment approach minima values (OCA/OCH, MDA/MDH, etc.) can be encoded using the attributes of the Minima class, which is associated with the FinalLeg through the ApproachCondition class. The following diagram shows the relevant classes and attributes.
Note: the diagram also shows that a CirclingArea may have ApproachCondition and associated Minima, as explained in the Circling Area section.
The minima values are encoded under the object Minima. For each ApproachCondition instance, an altitude and a height can be encoded. The altitudeCode attribute may have the values 'OCA' (obstacle clearance altitude) or 'MDA' (minimum decision altitude). The reference (mean sea level) is encoded in the altitudeReference attribute, with the value 'MSL'. Similarly, if the height is provided, the value is encoded in the attribute height, with the heightCode having as possible values 'OCH' or 'MDH', respectively. The heightReference may have the values 'HAA' (height above aerodrome) or 'HAT' (height above threshold). The reference is usually indicated on the instrument approach chart and / or it may be provided by the procure design office.
The climbGradient attribute of the ApproachCondition class corresponds to the climb gradient of the missed approach legs. It is intended to be used for encoding non-nominal climb gradients, in combination with the aircraft landing category (such as “category A with 2% climb gradient”).