Thanks again Sigwx … the Arabian Sea piece is new to me, but the NAT stuff I know quite a lot about.

Proactivity in terms of offering levels started around 2014 as the ATM system that the controllers in Prestwick (Shanwick) & Gander have, have tools built in to them that (a) ‘hunt’ for higher levels for each flight (a rather blunt but generally reasonable assumption that efficiency improves at higher flight levels), and/or (b) ‘hunt’ to get flights who were not allocated the clearance/trajectory they’re requested, changes to get back to that requested trajectory. The hunting takes place fairly regularly and it sends prioritised messages to the controllers when changes are possible so that they can be actioned quickly. Before these new tools were introduced (first by Gander and then by Shanwick) this was a manual thing that human’s rarely found time to do as oceanic controllers handle a huge amount of traffic simultaneously when compared to continental controllers. Performance data is available to inform how effective the process is - but it’s truly a complex issue to interpret it as there can be many reasons why crews don’t want the improvements/original trajectories (!)

The variable Mach change was enabled in the spring of 2019 within this airspace when space based ADS-B from the Aireon system went live (from memory, a little earlier in BIRD as they had a fair amount of ground based SSR and ADS-B before then and had done some of the concept development work already). ATS Surveillance really was a game changer here as accurate position information is received around every 2-3 seconds, instead of the 14 minute ADS-C contracts, thus enabling more frequent tracking of trajectories and effectively removing the need to apply fixed Mach numbers for a substantial proportion of flights. Now, controllers have to get used to working this way so the performance of this change has built progressively since and I looked at the performance the other day and the number of minutes when variable Mach has been assigned since it went live is really outstanding (IMHO).

My reflections around this are relatively simply …. Airlines fund these service improvements and, as an ANSP, it’s only responsible to squeeze every ounce of benefit out of it. As an ANSP I can tell you it benefits everyone. The NAT is safer now than it was before, less fuel is being burned (and in turn uplifted/carried) with corresponding reductions in GHG emissions too. The investment in ground infrastructure is needed but, again in my experience, it’s a fairly modest investment for what you get in return !