Aircraft Operations

Chapter 2
ACCURACY OF FIXES
2.1 GENERAL
Fixes and points used in designing flight procedures are normally based on standard navigation systems.
2.2 FIX FORMED BY INTERSECTION
Because all navigation facilities and waypoints have accuracy limitations, the geographic point which is identified is
not precise but may be anywhere within an area called the fix tolerance area which surrounds its plotted point of
intersection. Figure I-2-2-1 illustrates the intersection of two radials or tracks from different navigation facilities.
2.3 FIX TOLERANCE FACTORS
2.3.1 The dimensions of the fix tolerance area are determined by the system use accuracy of the navigation aid(s)
on which the fix is based, and the distance from the facility.
2.3.2 System use accuracy is based on a root sum square calculation using the following tolerances:
a) ground system tolerance;
b) airborne receiving system tolerance; and
c) flight technical tolerance.
See Table I-2-2-1 for system use accuracies and Table I-2-2-2 for the tolerances on which these values are based.
2.4 FIX TOLERANCE FOR OTHER TYPES OF NAVIGATION SYSTEMS
2.4.1 Surveillance radar
Radar fix tolerances are based on radar mapping accuracies, azimuth resolution, flight technical tolerance, controller
technical tolerances, and the speed of aircraft in the terminal area. The fix tolerances are listed below:
a) terminal area surveillance radar (TAR) within 37 km (20 NM): fix tolerance is ±1.5 km (0.8 NM); and
b) en-route surveillance radar (RSR) within 74 km (40 NM): fix tolerance is ±3.1 km (l.7 NM).
I-2-2-1 23/11/06