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

Appendix A to Chapter 1
VOR AND NDB ROUTES — REFINED METHOD FOR
THE CONSTRUCTION OF OBSTACLE CLEARANCE AREAS
1. GENERAL
1.1 Scope
The “refined method” presented in this appendix, related to obstacle clearance criteria for the en-route phase of an IFR
flight, can be used when the criteria contained in Chapter 1 are not sufficient to address particular obstacle constraints.
The criteria presented in this appendix amplify and/or modify the criteria as presented in Chapter 1.
2. OBSTACLE CLEARANCE AREAS
2.1 Primary and secondary areas
The obstacle clearance area is divided into a central primary area and two lateral secondary areas which replace the
buffer areas in the standard method as described in Chapter 1.
2.2 Reductions to secondary area widths
Secondary areas for en-route operations may be reduced when justified by factors such as:
a) when there is relevant information on flight operational experience;
b) regular flight inspection of facilities to ensure better than standard signals; and/or
c) radar surveillance.
3. OBSTACLE CLEARANCE
The criteria as contained in Chapter 1 apply. The MOC of the secondary area tapers from the full MOC of the primary
area to zero at the outer edge.
II-3-1-App A-1 23/11/06