3D software-2

28.10.2004

Submission:

In short, my opinion is if there is a penetration of the protection surface by the PANS-OPS criteria and the 3D surface as defined by the software is not showing it, then the 3D surface is not well defined in the software.
PANS-OPS does not define secondary protection surfaces as constant slope surfaces. Only in the case when the width of the secondary area is constant, the slope of the surface will be the same abeam any point on the approach flight path. When the protection area splays, the secondary area surface becomes a curved surface with its slope, measured perpendicular to the flight path, reducing proportionally to the increase in the area width. I tried to illustrate this in the accompanying diagram representing a typical approach segment along a VOR radial in plan and three cross-sections. It is clearly visible that the slope of the secondary area reduces width the increase in the total width of the protection area (S3<S2<S1).

This change in the slope, as well as the actual gradient of the slope is irrelevant to the procedure designer since the basic rule of linear reduction in MOC, from full at the inner edge to zero at the outer edge of the secondary area, applies abeam any point of the flight path.

Obrad Puskarica

Senior Navigation Procedures Specialist _ Airways Corporation of New Zealand