The TerminalArrivalArea supports the encoding of similar information as the MSA, but in relation with Terminal Arrival Altitude (TAA) as defined by ICAO PANS-OPS, which is used for T or Y-bar RNAV procedures. The standard TAA has three reference “branches”areas, based on the direction of the approach. This information is encoded in the arrivalAreaType attribute with one of the values: 'STRAIGHT_IN', 'RIGHT_BASE' or 'LEFT_BASE'.
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For each arrivalAreaType value, a two different SignificantPoint should may be associated with the TerminalArrivalArea for the association with role IAF, one providing the reference for distances (with role IAF) and one for angles (with role IF). For the straight-in sector, the IAF and the IF are typically the same, therefore only one of the two associations is needed.
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An issue has been recorded with the AIXM CCB (AIXM-256) reporting a bug: the association names are swapped. The correct reading is that:
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The relationships between the TAA and the IAF / IF are modelled through the associations isUsedForAngle and isUsedForDistance. The SignificantPoint choice in this case is limited to the role fixDesignatedPoint, due to the fact that the model is applicable to the RNAV procedures (i.e. waypoints).
Each TerminalArrivalArea may have one or more TerminalArrivalAreaSector objects, in case stepdown arcs and subsectors are defined. Most TerminalArrivalArea will have a single associated TerminalArrivalAreaSector. Each TerminalArrivalAreaSector isDescribedBy a CircleSector.
The CircleSector class is used in order to provide the attributes necessary to describe the the TAA sector geometry, including the value of the TAA minimum altitude defined for that particular area sector. The circular sector is defined between the fromAngle and the toAngle. As indicated above, the fromAngle and the toAngle are based on the IF SignificantPoint (not the circular sector centre, which may be different, e.g. IAF). To indicate if the direction of the arc is clockwise or counterclockwise, the attribute arcDirection is used with the values 'CWA' (clockwise) and 'CCA' (counterclockwise).
For a single sector (no stepdown / subsectors defined) the radius of the sector is encoded in the outerDistance attribute. The innerDistance is relevant for the encoding of sub-sectors, especially for the outer sub-sectors (for the sub-sectors starting from the IAF/IF, the innerDistance can be encoded with 0 KM/NM or left empty).
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