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

III-2-3-2 Procedures — Aircraft Operations — Volume II
designed. This distance is the sum of the minimum stabilization distances required at the IAF and IF and can be derived
from Table III-2-1-3 or Table III-2-1-9.
Note.— The optimum length of 9.3 km (5.0 NM) ensures that the minimum segment length for aircraft IAS up to
390° km/h (210 kt) below 3 050 m (10 000 ft) will be accommodated.
3.2.3 Descent gradient. The optimum descent gradient is 4% (Cat H, 6.5%). Where a higher gradient is necessary
to avoid obstacles, the maximum permissible is 8% (Cat H, 10%). Descent gradient is based on the shortest possible
track distance (TRD) for the fastest category of aircraft, and not the segment length.
3.2.4 Calculation of track distance (TRD). The TRD between two fly-by waypoints is defined as the segment
length reduced by the stabilization distance at both turns (r tan /2) and increased by the distance flown in the turn from
abeam the waypoint to the tangent point (2r ×0.5/360).
TRD = segment length – r(tan 1/2 + tan 2/2) + r(1 + 2)/360
where:
23/11/06
1 = turn angle (degrees) at the beginning of the segment
2 = turn angle (degrees) at the end of the segment
r = turn radius at 25° bank angle
Example for a first 110° turn and a second 70° turn:
TRD = segment length – 0.56r
3.2.5 Shortest initial approach segments. For the offset initial approach segments, the shortest possible track
distance will occur when a 110° turn is made at the IAF and a 70° turn is made at the IF for a Y-bar procedure and when
a 90° turn is made at either the IAF or the IF for a T-bar procedure. For the central initial approach segment, the
shortest possible track distance will occur when a 90° turn is made at the IAF.
3.2.6 Procedure entry altitude. The procedure is entered at the 46 km (25 NM) minimum sector altitude or
terminal arrival altitude. Where the initial approach waypoint forms part of an air route, the procedure should be entered
at the minimum en-route altitude applicable to the route segment.
3.2.7 Reversal procedures. When all three initial segment legs are implemented there is no need for reversal
procedures. Should one of the legs not be implemented, a racetrack pattern may be established at either or both of the
other IAFs. In the event that the central IAF leg is one of the remaining legs, its capture region is adjusted to
accommodate normal sector entries into a reversal procedure (see Figure III-2-3-3).
3.2.8 Holding. A holding pattern may be provided at any IAF and should be aligned with the initial segment track.
3.3 INTERMEDIATE APPROACH SEGMENT
3.3.1 Alignment. The intermediate approach segment should be aligned with the final approach segment whenever
possible. If a turn at the FAF is necessary it shall not exceed 30°.