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

Part III — Section 3, Chapter 6 III-3-6-9
6.4.8.5 Calculation of OAS heights
To calculate the height z of any of the sloping surfaces at a location x’, y’, the appropriate constants should be first
obtained from the PANS-OPS OAS CD-ROM. These values are then substituted in the equation z = Ax' + By' + C. If it
is not clear which of the OAS surfaces is above the obstacle location, this should be repeated for the other sloping
surfaces. The OAS height is the highest of the plane heights (zero if all the plane heights are negative).
Note.— The PANS-OPS OAS CD-ROM also contains an OCH calculator that will show the height of OAS surface
Z above any X, Y location. It includes all the adjustments specified for ILS geometry, aircraft dimensions, missed
approach climb gradient and GBAS RDH.
6.4.8.6 OAS template construction
Templates, or plan views of the OAS contours to map scale, are sometimes used to help identify obstacles for detail
survey (see Figure III-3-6-10). The OAS data on the PANS-OPS OAS CD-ROM includes the coordinates of the points
of intersection of the sloping surfaces at threshold level and at 300 m above threshold level for Cat I (see Figure III-3-
6-11). The intersection coordinates at threshold level are labelled as C, D and E.
6.4.8.7 Adjustment of OAS constants
6.4.8.7.1 General. The following paragraphs describe the adjustments which may be made to the OAS constants.
These adjustments are mandatory when the standard conditions are not met (See 6.1.3, “Standard Conditions”).
Optional adjustments may be made when so specified. For examples of calculations see Instrument Flight Procedures
Construction Manual (Doc 9368).
6.4.8.7.2 Reasons for adjusting constants. The constants may be modified by the PANS-OPS OAS CD-ROM to
account for the following:
a) dimensions of specific aircraft;
b) the height of the GBAS DCP;
c) GBAS course width greater than 210 m at threshold; and
d) missed approach climb gradient.
6.4.8.7.3 Specific aircraft dimensions. An adjustment is mandatory where aircraft dimensions exceed those
specified in 6.1.3, “Standard conditions” and is optional for aircraft with smaller dimensions. The PANS-OPS OAS
CD-ROM adjusts the OAS coefficients and template coordinates for the standard dimensions of category A, B, C, D,
and DL aircraft automatically. It will do the same for specific aircraft dimensions in any category. It uses the following
correction formula to adjust the coefficient C for the W, W*, X and Y surfaces:
W surface: Cwcorr = Cw –(t–6)
W* surface: Cw*corr = Cw*–(t–6)
X surface:Cxcorr = Cx –Bx ×P
Y surface:Cycorr = Cy –By ×P
23/11/06