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

Part II — Section 1, Chapter 1 II-1-1-7
1.4.6 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.
1.4.7 Obstacle clearance of the precision segment
application of basic ILS surfaces
1.4.7.1 General. The area required for the precision segment is bounded overall by the basic ILS surfaces defined
in 1.4.7.2, below. In standard conditions there is no restriction on objects beneath these surfaces (see 1.1.3, “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.
1.4.7.2 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-1-1-6).
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;
c) the missed approach surface. This is a sloping surface which:
1) starts at a point 900 m past the threshold (Cat H, a starting point of 700 m past the threshold can be
considered if necessary) at threshold elevation;
2) rises at a 2.5 per cent gradient; and
3) splays so as to extend between the transitional surfaces. It extends with constant splay to the level of the
inner horizontal surface. Thereafter, it continues at the same gradient but with a 25 per cent splay until the
termination of the precision segment; and
d) the extended transitional surfaces, which continue longitudinally along the sides of the approach and missed
approach surfaces and up to a height of 300 m above threshold elevation.
1.4.7.3 Determination of OCA/H with basic ILS surfaces
1.4.7.3.1 Where the basic ILS surfaces specified in 1.4.7.2 are not penetrated, the OCA/H for Category I and
Category II is defined by the margins specified in Table II-1-1-2, and Category III operations are not restricted.
Obstacles may be excluded when they are below the transitional surface defined by Annex 14 for runways with code
numbers 3 and 4, regardless of the actual runway code number (i.e., the surfaces for code numbers 3 and 4 are used for
the obstacle assessment on runways with code numbers 1 and 2).
1.4.7.3.2 If the basic ILS surfaces listed above are penetrated by objects other than those listed in Table II-1-1-3,
the OCA/H may be calculated directly by applying height loss/altimeter margins to obstacles (see 1.4.8.8,
“Determination of OCA/H with OAS or basic ILS surfaces”).
23/11/06