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

III-3-6-2 Procedures — Aircraft Operations — Volume II
Note 2.— The dimensions shown are those which encompass current aircraft types They are chosen to facilitate
OCA/H calculations and promulgation of aircraft category related minima. It is assumed that these dimensions are not
intended to be used for other purposes than the OCA/H calculations in other ICAO documents. The use of OAS
surfaces to calculate OCA/H may result in significant differences between aircraft categories because of small
differences in size. For this reason, it is always preferable to use the Collision Risk Model (6.4.9) which will allow for
more realistic assessment for both height and position of obstacles.
Note 3.— Current Category E aircraft are not normally civil transport aircraft and their dimensions are not
necessarily related to Vat at maximum landing mass. For this reason, they should be treated separately on an
individual basis.
b) Missed approach climb gradient: 2.5 per cent.
c) GBAS course width: 210 m at threshold.
d) Glide path angle:
23/11/06
1) minimum/optimum: 3.0°;
2) maximum: 3.5°;
e) GBAS reference datum height: 15 m (50 ft).
f) All obstacle heights are referenced to threshold elevation. A declaration by the procedure designer shall be
made for the value of undulation (N) at each runway threshold.
g) The delta length offset is zero.
6.1.3.1 Final approach segment (FAS) data. The final approach segment is defined by data prepared by the
procedure designer. The accuracy of the path is therefore totally dependent on the accuracy and integrity of the original
data on the runway and calculations carried out by the designer. The total description of the path, including the
glide-path, lateral guidance sector width, alignment and all other parameters describing the path are originated by the
designer and are not affected by the location of ground facilities. The path parameters are designed using geodetic and
geometric calculations and the parameters are formatted into a FAS data block in electronic media as described in the
appendix to this chapter. Data are then added to provide a cyclic redundancy check (CRC), and the complete block is
transferred to users to insure the integrity of the data throughout the process leading to inclusion of the path data in the
GBAS system for transmission to user airborne systems. A complete description of the FAS data block is included in
Doc 9368, Instrument Flight Procedures Construction Manual, Attachment C.5, along with an example of the process
and product.
6.1.4 Obstacle clearance altitude/height (OCA/H)
The GBAS criteria enable an OCA/H to be calculated for each category of aircraft. See Part I, Section 4, Chapter 1, 1.8,
“Categories of aircraft”. Where statistical calculations were involved, the OCA/H values were designed against an
overall safety target for risk of collision with obstacles of 1 × 10 -7 , i.e. 1 in 10 million per approach. The OCA/H
ensures clearance of obstacles from the start of the final approach to the end of the intermediate missed approach
segment.
Note.— This OCA/H is only one of the factors to be taken into account in determining decision height as defined in
Annex 6.