It appears that these 2 sources of information contradict each other regarding contingencies, MNPS guidance states to go 15 nms offset, while Doc 7030 states to go midway between two tracks which is 30nms!
On the face of it yes, but
my own take on this is that they don't necessarily contradict, but in addition to the standard 15 NM offset and descent, further consideration should be given by crews of non-MNPS/RVSM aircraft in relation to descending through the OTS from F430+ to F280-. Put simply, everyone does a 15NM offset as standard, but in the event that you're non-MNPS/RVSM descending through tracks from F430+ you
should also consider going for the mid-point from F410 on down. Again, and I stress,
my own interpretation.
so please dont be surprised that crews don't totally understand what you expect them to do
To be honest, I'm not sure how much weight to place on the SUPPS either, given that certain elements fail to appear in either the 007/4444/MATS 2, but they're out there for all to see and I did suggest it "
should provide answers to more general questions." Until I'm told otherwise I'll stick to the MATS 2; whose wording is extracted from Doc007 Chapter 13.
What an a/c descending through MNPS airspace from above 420 should do should be no different to what an a/c starting at 360 should do, surely?
Traffic at F360 is within MNPS airspace and is therefore MNPS certified; having all the benefits of reduced lateral/longitudinal separation. Non-MNPS traffic above F420 does not have the required Nav capability/accuracy/redundancy to enjoy the reduced MNPS separation and must therefore be treated differently from those who are MNPS certified. (Lateral separation for example is increased to 120 NM as opposed to the 60 NM for those having MNPS certification). I assume that is what those at ICAO were considering when they advise non-MNPS to go for the mid-point (currently placing an a/c 30NM from the adjacent tracks).
My bedside reading says more important to put myself between and parallel to fixed tracks than to simply fly an immaculate 15nm offset on my random track.
Couldn't agree more, but what you're suggesting doesn't (yet) appear in the 007/4444/MATS 2 and only appears to exist in a "working document" (SUPPS); suggesting to me that whilst not in the documents mentioned, it should be a consideration for crews of non-MNPS/RVSM descending through OTS.
I imagine that discussions elsewhere precisely along these lines have resulted in the appearance in the SUPPS of such. As I see it the issue, other than not appearing where you would expect/hope to find it, is that going for the mid-point is equally as sensible for MNPS certified as it is non-MNPS certified when descending from a position directly above the OTS to a position below. (The advantage for MNPS certified a/c having to go for only a 15NM offset is that a descent could possibly commence earlier than might otherwise be the case if having to delay until reaching the midpoint).