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

Part III — Section 1, Chapter 3 III-1-3-3
3.4 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 that 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).
3.5 SYSTEM COMPUTATIONAL TOLERANCE
The system computational tolerance (ST) is ±0.46 km (0.25 NM). This tolerance is based on the implementation of
WGS-84.
3.6 XTT, ATT AND AREA SEMI-WIDTH
3.6.1 XTT and ATT
3.6.1.1 The combination of the tolerances specified in 3.3 to 3.5 on a root sum square basis gives the cross-track
and along-track tolerance of any fix defined by waypoints as follows.
where: DTT = DME system use accuracy
ST = System computation tolerance
FTT = Flight technical tolerance
XTT = ± (DTT 2 +FTT 2 +ST 2 ) ½
ATT = ± (DTT 2 +ST 2 ) ½
3.6.1.2 Results of calculations of XTT, ATT for enroute, IAF, IF, FAF, MAPt, and TP are presented in
Tables III-1-3-1, III-1-3-2, III-1-3-3 and III-1-3-4. For departures, the XTT and ATT can be derived from column
FAF/MAPt/TP. A fix coincidental with the DER needs a special calculation taking into account an FTT of ±0.185 km
(±0.1 NM) (see formulas in the Appendix).
3.6.1.3 In departures the area width at the first waypoint depends on the assumed height of the aircraft. A
departure climb gradient of 3.3 per cent or equal to the procedure design gradient if greater than 3.3 per cent should be
applied to obtain this height.
23/11/06