NAT/MNPSA Ops.

[BOAC]

Let's hope that commonsense prevails, then, when the documentation catches up

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.

.- I'm afraid I do not understand the logic here. I would suggest that very little traffic operating above the MPNS levels is not 'certified' - I suspect it almost certainly is but simply wants to fly higher, but indeed going for the mid-point is sensible to 'cover all'. However, going back to the OP, on which track does one base your (existing) 15nm offset for descent? I would choose the same 'mid-point'.

[rab-k]

At a guess, I'd say 10% of the traffic above F420 is non-MNPS certified. The mid-point technique in SUPPS would appear to be directed specifically at those 10% who, at the time a descent is required and no prior ATC clearance can be obtained, find themselves positioned directly above the OTS.

As for the remainder, (those who are MNPS certified irrespective of FL, all non-MNPS F280- plus those non-MNPS F420+ not above the OTS), where no prior ATC clearance can be obtained, the standard 45 degree turn to acquire a 15 NM offset would apply. The turn being either side of your cleared track, i.e. the route specified in the Oceanic Clearance; whether you're cleared to follow an organised track or a random route.

The problem in going for the mid-point between tracks, which was formerly the procedure for all, was that on 9/11 the multiple turnbacks and mid-ocean diversions which occurred resulted in everybody that was on an organised track heading for the same point, which just created further issues as you can imagine. Any future repeat of this was resolved by a 15NM offset being introduced. (as opposed to the 30NM which had been the case previously - organised tracks being 60NM apart). This procedure was adopted for all flights whether on organised track or random route.

I'd suggest that these days the mid-point between a pair of organised tracks only becomes a factor if non-MNPS aircraft above the OTS require to descend without a clearance; being non-MNPS possibly resulting in having a reduced degree of certainty/accuracy as to position in relation to the OTS. (Not that even the mid-point between organised tracks is guaranteed to be traffic-free as we do have randoms which may route between two or more tracks - these being cleared subject to traffic density on a fairly irregular basis).

In the case of MNPS certified F420+ whose route is crossing/converging with, rather than running parallel to, the OTS; if having offset 15NM from the cleared route you end up heading towards an organised track whilst in the descent, I'm certain good airmanship would result in part of the descent profile being a dog-leg to acquire a 15NM offset parallel to the organised track being infringed, rather than simply steaming through it, until such time as reaching a level below the organised tracks.

In the case of non-MNPS as per the above scenario, the mid-point between a pair of organised tracks would be my own preferred option; simply due to the non-MNPS Nav capability whereby the 15NM offset you think you have acquired, in order to run parallel to an organised tack, might in reality be <15NM.

Hope that makes sense.