Aircraft Operations. Volume II - Construction of Visual and Instrument ...

III-1-3-4 Procedures — Aircraft Operations — Volume II
23/11/06
3.6.2 Area semi-width
3.6.2.1 Area semi-width (1/2 A/W) at a waypoint is determined by the following equation:
where: 1.5 XTT corresponds to 3 sigma
½A/W=XTTx1.5+BV
BV = Buffer value (for values see Table III-1-3-5)
3.6.2.2 Results of calculations of the semi-width are shown in Tables III-1-3-1, III-1-3-2, III-1-3-3 and III-1-3-4.
For example calculations see the appendix to this chapter. For departures, the area semi-width can be derived from
column FAF/MAPt/TP (see example calculations in the appendix to this chapter).
3.7 VIABILITY CHECK OF THE PROCEDURE
3.7.1 Viability check
A theoretical and operational viability check should be made of the route, including the effect of the waypoints’ location
and the (DME) environment on FMC performance.
3.7.2 Initial evaluation
An initial evaluation should be made using flight simulators and/or FMC simulation software tools to check the
predicted flight path for continuity and repeatability of the route. Such evaluations should include the effect of minimum
and maximum IAS, winds, and type of aircraft and FMC. The procedure should, where appropriate, be flown from
different directions, since the facilities used for update depend on the direction of the flight.
3.7.3 Pre-promulgation flight check
The pre-promulgation flight check should include an analysis of the update history (use of DME stations for update). If
the FMC uses DME stations outside their promulgated radio range, an additional check on the effect of the use of those
stations should be made.
3.8 REVERSION MODE CHECKS
3.8.1 VOR/DME. The navigation computer mode may change from the DME/DME mode to the VOR/DME mode.
It is assumed that the VOR/DME station closest to the route will be selected by the navigation computer for this
purpose. Since the accuracy of that station may differ from the DME/DME accuracy, a check must be made of the effect
of the navigation reversion mode. Therefore, for each segment along the route, the ½ AW must be determined based on
tangent point distance (D1) and distance to tangent point (D2) from the VOR/DME station within range which is closest
to the route. See Chapter 4, 4.5, “XTT, ATT and area semi-width”.
3.8.2 Basic GNSS. Chapter 2, 2.5, “XTT, ATT and area semi-width” gives equivalent information for basic GNSS
areas, which must also be checked if this is an option for the procedure.