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

III-1-4-2 Procedures — Aircraft Operations — Volume II
23/11/06
4.3 FLIGHT TECHNICAL TOLERANCE
The flight technical tolerance (FTT) will vary with the type of position indicator used in the cockpit instrumentation.
For the arrival phase, the FTT also depends on the location of the IAF. It is assumed that the FTT has the following
contributions to the cross-track tolerance:
a) departures:
b) arrival:
1) ±0.19 km (±0.10 NM) at the DER; and
2) 0.93 km (0.50 NM) for all other fixes;
1) FAF located more than 46 km (25 NM) from IAF: 3.70 km (2.00 NM); and
2) FAF located within 46 km (25 NM) of IAF: 1.85 km (1.00 NM);
c) initial and intermediate approach: ± 1.85 km (1.00 NM); and
d) final and missed approach: ± 0.93 km (0.50 NM).
4.4 SYSTEM COMPUTATION TOLERANCE
The system computation tolerance (ST) is assumed to be 0.93 km (0.50 NM).
4.5 XTT, ATT AND AREA SEMI-WIDTH
4.5.1 XTT and ATT
4.5.1.1 The combination of the tolerances specified in 4.2.2 to 4.4 on a root sum square basis gives the cross-track
tolerance (XTT) and the along-track tolerance (ATT) of any fix as follows:
(see Figures III-1-4-1 and III-1-4-2)
where:
XTT = ± [VT 2 +DT 2 +FTT 2 +ST 2 ] 1/2
ATT = ± [AVT 2 +ADT 2 +ST 2 ] 1/2
D is the distance from the reference facility to the waypoint; D = [D1 2 +D2 2 ] 1/2
D1 is the tangent point distance. The tangent point is the perpendicular projection of the reference facility onto
the nominal track. The tangent point distance (D1) is the distance from the reference facility to the tangent point.
D2 is the distance to the tangent point. This is the distance from the waypoint to the tangent point (see
Figure III-1-4-1).