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

II-3-1-App B-2 Procedures — Aircraft Operations — Volume II
2.4.3 Use of DME. If available, DME can be used as a turning point fix. For DME accuracy values, see Part I,
Section 2, Chapter 2, 2.4.4, “DME”.
2.4.4 Facility tolerances – To be developed
3.1 Primary area splay
3.1.1 The primary area splays at an angle of:
a) 5.7° (10%) — VOR; and
b) 7.95° (14%) — NDB.
23/11/06
3. SPLAY
3.1.2 Primary area splay calculations. These values are calculated as the root sum square of the system use
accuracies values as given in 2.2 and 2.3. This gives a 95 per cent probability of containment (2 SD) of ± 9.87 per cent
(5.64°) in the case of VOR, and ± 13.96 per cent (7.95°) in the case of NDB. The value of the primary area limit is
rounded up to ± 10 per cent (5.7°) in the case of VOR. The value of the primary area limit is rounded up to ± 14 per
cent (8.0°) in the case of NDB.
3.2 Buffer area/secondary area splay. The buffer area/secondary area splays at an angle of:
a) 9.1° (15.86%) — VOR; and
b) 13.0° (23%) — NDB.
3.3 VOR buffer area/secondary area splay calculations. In the calculation of the 99.7 per cent probability of
containment (3 SD), the value of ± 1.0° for the monitor tolerance is taken into account to replace 1.5 x 3.5° for the
ground system tolerance by a maximum value of 3.5° + 1.0° = 4.5°. The combination on a root sum square basis gives
a 3 SD limit of ± 14.08 per cent (8.01°). An additional value of ± 1.0° is added, resulting in a total area limit of ±15.86
per cent (9.01°). The splay of the total area is rounded up to ± 16 per cent (9.1°). (See Figure II-3-1-2 of Chapter 3.)
3.4 NDB buffer area/secondary area splay calculations. The calculation of the 99.7 per cent probability of
containment (3 SD) and the addition of a ± 1.0° buffer results in a total area limit of ± 22.94 per cent (12.92°). The
splay of the total area is rounded up to ± 23 per cent (13.0°).
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