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

III-3-6-10 Procedures — Aircraft Operations — Volume II
where:
P = [t/Bx or s + (t-3)/Bx ), whichever is the maximum] – [6/Bx or 30 + 3/Bx , whichever is the maximum]; and
s = semi-span
t = vertical distance between paths of the GP antenna and the lowest part of the wheels.
6.4.8.7.4 Height of the datum crossing point (RDH). The constants are based on a reference datum height (RDH)
of 15 m. An adjustment to the OAS constants is mandatory for an RDH less than 15 m, and is optional for an RDH
greater than 15 m. The PANS-OPS OAS CD-ROM adjusts the OAS coefficients and template co-ordinates by
correcting the tabulated values of the coefficient C for the W, W*, X and Y surfaces as follows:
Ccorr =C+(RDH–15)
where: Ccorr = corrected value of coefficient C for the appropriate surface
23/11/06
C = tabulated value.
6.4.8.7.5 GBAS course width greater than 210 m at threshold. Where the GBAS course width at threshold is
greater than the nominal value of 210 m, the collision risk model (CRM) method described in 6.4.9 shall be used.
Adjustments for sector widths less than 210 m shall not be made, and are inhibited on the PANS-OPS OAS CD-ROM.
6.4.8.7.6 Missed approach gradient. If missed approach climb gradients better than the nominal 2.5 per cent can
be achieved, the Y and Z surfaces may be adjusted. This is done by selecting the desired missed approach climb
gradient in the PANS-OPS OAS CD-ROM. The programme then adjusts the Y and Z surface constants.
6.4.8.8 Determination of OCA/H with OAS
6.4.8.8.1 General. The OCA/H is determined by accounting for all obstacles which penetrate the basic ILS
surfaces defined in 6.4.7.2 and the OAS applicable to the GBAS Category I operation being considered. The
exemptions listed in 6.4.7.3, “Determination of OCA/H with basic ILS surfaces” for obstacles penetrating the basic ILS
surfaces may be applied to obstacles penetrating the OAS, providing the criteria listed in that paragraph are met. For
GBAS Category I operations ILS Cat I OAS apply.
6.4.8.8.2 Calculation of OCA/H values with OAS. Accountable obstacles, as determined below in 6.4.8.8.2.1,
“OCA/H calculation steps”, are divided into approach and missed approach obstacles. The standard method of
categorization is as follows. Approach obstacles are those between the FAP and 900 m after threshold (Cat H, 700 m if
necessary). Missed approach obstacles are those in the remainder of the precision segment (see Figure III-3-6-12).
However, in some cases this categorization may produce an excessive penalty for certain missed approach obstacles
(see Attachment to Part II, 1.9). Where desired by the appropriate authority, missed approach obstacles may be defined
as those above a plane surface parallel to the plane of the glide path and with origin at -900 m (Cat H, –700 m if
necessary) (see Figure III-3-6-13), i.e. obstacle height greater than (900 + x) tan θ.
6.4.8.8.2.1 OCA/H calculation steps
a) Determine the height of the highest approach obstacle.
b) Convert the heights of all missed approach obstacles (hma) to the heights of equivalent approach obstacles (ha)
by the formula given below, and determine the highest equivalent approach obstacle.