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 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'.
For each arrivalAreaType value, two different SignificantPoint may be associated with the TerminalArrivalArea, 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.
An issue has been recorded with the AIXM CCB (AIXM-256) reporting a bug: the association names are swapped. The correct reading is that:
- the association with role name IAF is used to provide the distance
- the association with the role name IF is used to provide the angle.
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 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).
The value of the minimum altitude in the respective TerminalArrivalAreaSector is encoded in the lowerLimit attribute. The lowerLimitReference should have the value 'MSL' (according to the PANS-OPS definition of a altitude).
Each TerminalArrivalAreaSector may have its geometry also represented as a Surface object, mainly intended for graphical applications.