Mountainous Terrain Application in Holds

04.10.2011

Submission:

We currently apply an additional 300m in the primary and buffer areas when assessing a hold in mountainous terrain (see figure II-4-1-4). This means that in the 4-5NM buffer we would apply 360m MOC. I understand others would apply 120m in this situation and I would like to know what is done in different countries.

There is also an issue with the buffer of helicopter holds where table II-4-1-1 describes the buffer as having a linear MOC of 300m to 0m and figure-4-1-5 shows stepped MOC as is applied to aircraft holding.

Greg Perris - Procedure Designer – Airways - New Zealand


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Answer or Commentary:

I. W.

I interpret Pans-Ops differently concerning Mountainous terrain. As far as I understand it, applying increased MOC is a function (i.e. multiplier) of the MOC in use.

In Part I — Section 2, Chapter 1 paragraph 1.7 INCREASED ALTITUDES/HEIGHTS FOR MOUNTAINOUS AREAS, Pans-Ops States:

“Where these conditions are known to exist, MOC should be increased by as much as 100 per cent.”

So in one of the holding buffer areas with a MOC of 90m a 100% increase would be 90 x 2 = 180. I personally don't think it would be 390m.

I must admit that figure II-4-1-4 on page II-4-1-12 does seem to show the addition of a full 300m onto the buffer areas MOC.

However in Appendix B to Chapter 1 paragraph 4 states:

“This level will vary from a minimum of 300 m (984 ft) above obstructions within the holding area to 600 m”

It is the word “vary” that seems to imply a varying MOC

What do other procedure designers think?
Is the holding over mountainous terrain a special case?


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