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

I-4-2-2 Procedures — Aircraft Operations — Volume II
An arc may join a straight track at or before the initial approach fix. In this case, the angle of intersection of the arc and
the track should not exceed 120°.
When the angle exceeds 70°, a lead radial which provides at least a distance “d” of lead shall be identified to assist in
( α )
leading the turn (d = r.tan ; r = radius of turn; α = angle of turn).
2
2.1.2.1 Arrival routes 46 km or longer (25 NM)
23/11/06
2.1.2 Area construction
When the length of the arrival route is greater than or equal to 46 km (25 NM), en-route criteria apply to the 46 km
(25 NM) prior to the initial approach fix (IAF). The area width decreases from 46 km (25 NM) with a
convergence angle of 30° each side of the axis, until reaching the width determined by the initial approach criteria. See
Figure I-4-2-1.
2.1.2.2 Arrival routes less than 46 km (25 NM)
When the length of the arrival route is less than 46 km (25 NM), the area width decreases from the beginning of the
arrival route with a convergence angle of 30° each side of the axis, until reaching the width determined by the initial
approach criteria. See Figure I-4-2-2.
2.1.2.3 Turn protection
Turns will be protected by using:
a) en-route criteria for distances greater than 46 km (25 NM) from the IAF; and
b) initial approach criteria for distances of 46 km (25 NM) or less from the IAF.
2.1.2.4 Arrival based on a DME arc
In case of an arrival based on a DME arc, 2.1.2.1 and 2.1.2.2 apply with the following exceptions:
a) the distance is measured along the DME arc; and
b) the tapering is over a distance of 9.6 km (5.2 NM), measured along the DME arc.
The construction method is as follows. From the centre of the DME arc (point O), draw lines OA and OB which
intersect the limits at A1, A2, A3, A4 and B1, B2, B3, B4. Then, draw lines joining corresponding points A to B.
See Figures I-4-2-3 and I-4-2-4.
2.1.2.5 Basic GNSS receivers
2.1.2.5.1 In addition to the general arrival criteria, the following criteria apply. Cross-track tolerance (XTT),
along-track tolerance (ATT) and area semi-width for basic GNSS receivers are determined according to the formulae
defined in Part III, Section 1, Chapter 2, 2.5, “XTT, ATT and area semi-width”.