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

Part II — Section 3, Chapter 1 II-3-1-5
b) Outer edge of the turn. The outer edge of the turn area is composed of:
1) a straight extension of the outer edge of the segment before the turn;
2) the arc of a circle having a radius of T, which is centred on the turning point (nominal fix or facility); and
3) the tangent of the arc of this circle which makes an angle of 30° with the following segment.
The value of T is described by the following equation:
where: r = radius of turn
T=SA+2*r+E165°
E165° = wind effect to account for 120° course change plus 30° convergence angle plus 15° drift
SA = area semi-width
This method is based on the assumption that the size of the tolerance associated with the turn point is included
in the area corresponding to a straight segment.
Note 1.— Use the highest minimum altitude of all the segments intersecting at the turning point.
Note 2.— Maximum turn angle is 120°.
Note 3.— A constant wind effect (E165°) needs to be applied for all turn angles.
Example calculation for an altitude of 4 500 m. Given the turn parameters as stated in 1.4.3.3, “Turn
parameters” and area semi-width of 18.5 km, it follows that:
the radius of turn (r) = 16.77
wind effect (E165°) = 9.00
T = 18.5 + 33.54 + 9.00 = 61.04 km
c) Inner edge of the turn. From point K of the turn, draw a line making an angle of α/2 with the nominal track in
segment 2 (the segment following the turn). This line ends where it intersects the edge of segment 2.
d) End of turn area. The arc as described under (2) also denotes the end of the turn area.
1.4.3.5 Bidirectional routes. The method of construction of the turn area assumes a direction of flight. When the
route is to be flown in both directions, it is necessary to construct both turn areas to account for both directions of flight
and to apply the minimum obstacle clearance over the whole combined turn area (see Figure II-3-1-6).
1.5 MINIMUM ALTITUDES FOR SIGNAL RECEPTION
The minimum altitude en route based on VOR or NDB navigation, providing a minimum obstacle clearance, shall
allow a proper reception of the relevant facilities. The following formula can be used for planning purposes.
23/11/06