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

II-1-1-6 Procedures — Aircraft Operations — Volume II
23/11/06
1.4 PRECISION SEGMENT
1.4.1 General
The precision segment is aligned with the localizer course and contains the final descent for landing as well as the
initial and intermediate phases of the missed approach segment See Figure II-1-1-5.
1.4.2 Origin
The precision segment starts at the final approach point (FAP), that is, the intersection of the nominal glide path and the
minimum altitude specified for the preceding segment. The FAP should not normally be located more than 18.5 km
(10.0 NM) before threshold, unless adequate glide path guidance beyond the minimum specified in Annex 10 is
provided.
1.4.3 Descent fix
1.4.3.1 A descent fix may be located at the FAP to overcome certain obstacles located before the FAP as an
alternative to increasing the glide path (GP) angle. When so located, it becomes the final approach fix. The extension of
the precision surfaces into the precision segment is then terminated. The descent fix should not normally be located
more than 18.5 km (10.0 NM) before threshold, unless adequate GP guidance beyond the minimum specified in Annex
10 is provided. The maximum fix tolerance is ± 0.9 km (± 0.5 NM). Where DME is used to identify the fix, the range
shall be stated in tenths of kilometres (nautical miles).
Note.— Guidance material for determining the distance to the descent fix from the threshold is contained in
Appendix C.
1.4.3.2 Obstacle clearance at the descent fix. When a descent fix is provided, the precision approach surfaces start
at the earliest point of the FAF tolerance area (see Figure II-1-1-2). The provisions of Part I, Section 2, Chapter 2, 2.7.4,
“Obstacle close to a final approach fix or stepdown fix” which allow obstacles close to the fix to be ignored, apply in
the area below the 15 per cent gradient within the precision surfaces (Cat H, 15 per cent gradient or the nominal
gradient multiplied by 2.5, whichever is greater). Where a descent fix is not provided at the FAP, no curtailment of the
precision surfaces is permitted (see Figure II-1-1-3). If the precision surfaces are extended into the preceding segment,
they shall not be extended beyond the intermediate approach segment.
1.4.4 Glide path verification check
A fix (outer marker or DME) is necessary so as to permit comparison between the indicated glide path and the aircraft
altimeter information. The fix shall not have a fix tolerance exceeding ± 0.9 km (± 0.5 NM). When DME is used to
identify the fix, the range shall be stated in tenths of kilometres (nautical miles).
Note.— Guidance material for determining the height crossing the outer marker is contained in Appendix C.
1.4.5 Missed approach
The missed approach point is defined by the intersection of the nominal glide path and the decision altitude/height
(DA/H). The DA/H is set at or above the OCA/H, which is determined as specified in 1.4.7 to 1.4.9 and 1.5.