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

Part II — Section 1, Chapter 3 II-1-3-7
Note.— Guidance material for determining the distance to the descent fix from the threshold is contained in
Chapter 1, Appendix C.
3.4.3.2 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-1-3-3). 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-1-3-4). If the precision surfaces are extended into the
preceding segment, they shall not be extended beyond the intermediate approach segment.
3.4.4 Glide path verification check
A DME fix is necessary so as to permit comparison between the indicated glide path (elevation angle) and the aircraft
altimeter information. The fix shall not have a fix tolerance exceeding ± 0.9 km (± 0.5 NM). The range shall be stated
in tenths of kilometres (nautical miles).
Note.— Guidance material for determining the height crossing the DME fix is contained in Chapter 1, Appendix C.
3.4.5 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 3.4.7 to 3.4.9 and 3.5.
3.4.6 Termination
The precision segment normally terminates at the point where the final phase of the missed approach commences (see
Part I, Section 4, Chapter 6, 6.1.2, “Phases of missed approach segment”) or where the missed approach climb surface
Z (starting 900 m past threshold) reaches a height of 300 m (984 ft) above threshold, whichever is lower.
3.4.7 Obstacle clearance in the precision segment application of basic ILS surfaces
3.4.7.1 General. The area required for the precision segment is bounded overall by the basic ILS surfaces defined
in 3.4.7.2, below. In standard conditions there is no restriction on objects beneath these surfaces (see 3.1.3, “Standard
conditions”). Objects or portions of objects that extend above these surfaces must be either:
a) minimum mass and frangible; or
b) taken into account in the calculation of the OCA/H.
3.4.7.2 Definition of basic ILS surfaces. The surfaces to be considered correspond to a subset of Annex 14
obstacle limitation surfaces as specified for precision approach runway code numbers 3 or 4 (see Figure II-1-3-7).
These are:
a) the approach surface, continuing to the final approach point (FAP) (first section 2 per cent gradient, second
section 2.5 per cent as described in Annex 14);
b) the runway strip assumed to be horizontal at the elevation of the threshold;
23/11/06