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

Part III — Section 3, Chapter 6 III-3-6-7
6.4.7.2 Definition of basic ILS surfaces. The surfaces to be considered correspond to a subset of Annex 14
obstacle limitation surfaces specified for precision approach runway code numbers 3 or 4. These are (see
Figure III-3-6-5):
a) the approach surface continuing to the final approach point (first section 2 per cent gradient, second section
2.5 per cent gradient 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, and thereafter, 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 to a height of 300 m above threshold elevation.
6.4.7.3 Determination of OCA/H with basic ILS surfaces.
6.4.7.3.1 Where the basic ILS surfaces specified in 6.4.7.2 are not penetrated, the OCA/H for Category I is
defined by the margins specified in Table III-3-6-3. 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).
6.4.7.3.2 If the basic ILS surfaces listed above are penetrated by objects other than those tabulated in
Table III-3-6-2 the OCA/H may be calculated directly by applying height loss/altimeter margins to obstacles (see
6.4.8.8). The obstacles in Table III-3-6-2 may only be exempted if the GBAS course width meets the standard
condition of 210 m (see 6.1.3).
6.4.7.3.3 An object which penetrates any of the basic ILS surfaces and becomes the controlling obstacle, but
which must be maintained because of its function with regard to air navigation requirements, may be ignored under
certain circumstances in calculating the OCA/H, with the following provision. It must be established by the appropriate
authority that the portion which penetrates the surface is of minimum mass and frangibly mounted and would not
adversely affect the safety of aircraft operations.
6.4.8.1 General
6.4.8 Obstacle clearance of the precision segment using obstacle assessment
surfaces (OAS) criteria for GBAS operations
6.4.8.1.1 This section describes the OAS surfaces, the constants which are used to define these surfaces, and the
conditions under which adjustments may be made. The OAS dimensions are related to the GBAS geometry (GARP –
LTP distance, glide path angle), and the category of operation. (For GBAS only Category I apply). A table of OCA/H
values for each aircraft category may be promulgated for GBAS Cat I operations at the particular airfield.
23/11/06