North Atlantic Changes Timeline – updated 2021

By Mark Zee


This page has a timeline of big NAT changes, for the six Oceanic Area Control Centres (OACC’s): EGGX/Shanwick, CZQX/Gander, BIRD/Iceland, ENOB/Bodø, LPPO/Santa Maria, and KZWY/New York Oceanic.


  • The “MAX UPLINK DELAY VALUE TO 300 SECONDS” message will now be sent to all aircraft – and each time you logon to a new OACC. This change came in July 2021 with the new NAT Doc 007.
  • Datalink Mandate (back again). Shortly after the original Phase 3 of the Datalink Mandate came into force on 30 Jan 2020, the downturn in traffic on the NAT as a result of Covid (from around March 2020 onwards) saw a relief period, which expires on 25 Feb 2021. After this date, Phase 3 is back in force: all aircraft FL290-410 in the NAT region, with some geographic exceptions, require CPDLC and ADS-C. See article on Datalink Mandate.
  • No NAT Tracks experiment. Starting February 2021, Shanwick and Gander will experiment with not issuing any NAT Tracks on quiet days. See article. Update: The No NAT Tracks experiment ended in June 2021 – it’s over. There won’t be any further NAT OTS NIL days.


  • Datalink Mandate (suspended). Datalink is currently required between FL350-390 in the NAT region. From 30th Jan 2020 this mandate will be extended to between FL290-410, and will include the Tango Routes. There are exempted areas: North of 80N, Surveillance airspace (where ATC can see you on radar or ADS-B), and New York Oceanic East. If you have ADS-B and VHF, Gander will accept you on a line RATSU 61N20W 63N30W 62N40W 61N50W SAVRY or north of. Aircraft without datalink can request to climb/descend through datalink mandated airspace, but will only be considered on a tactical basis – most likely you’ll get stuck under FL290. Read the ICAO Bulletin for more info. Suspended in March due to Covid.


  • Micro-SLOP ATC don’t seem to like the term, but that’s basically what it is. Before, you could only SLOP centreline, 1NM or 2NM to the right. But from Aug 2019, Gander, Shanwick, Santa Maria and Bodo started allowing offsets right of centreline in tenths of a nautical mile up to a maximum of 2NM. From 12th Sep 2019, Iceland and New York Oceanic will allow this too. Check out our article for more info.
  • ASEPS. Reduced longitudinal separation (down to as close as 14NM) has been happening since April 2019 in Gander, Shanwick, and Santa Maria. But from Oct 2019, lateral separation will be reduced to 19NM from the previous PBCS limit of 25NM for compliant aircraft. To be able to get this reduced separation, you’ll need ADS-B and to be fully PBCS compliant (i.e. meet the specs of RNP4, RCP240 and RSP180). Read the ICAO Bulletin for more info.
  • OWAFS Operations Without a Fixed Speed. In other words, you get to decide how fast you fly. It’s been happening in the Shanwick, Santa Maria, and New York Oceanic FIRs since Apr 2019. Iceland say they will start doing this some time around Oct-Nov 2019. You get a normal oceanic clearance, with a fixed Mach Number, like you always did. But then somewhere after the Oceanic Entry Point, you may get a CPDLC message saying RESUME NORMAL SPEED. You should reply with WILCO. What that means is: Fly ECON, or a Cost Index with Variable Mach. You can fly within 0.01 up or down of your cleared Mach, but if it varies by 0.02 or more you must advise ATC. Read the ICAO Bulletin and check out our article for more info.
  • PBCS From March 29th 2019, there may be more than just three daily PBCS tracks. They will continue to be only FL350 to FL390 inclusive and only on the designated tracks during the period the tracks are in effect. There may be days where there are no PBCS tracks, 3 PBCS tracks, 5 PBCS tracks, potentially even all the tracks.
  • Contingency Procedures From March 29th 2019, new contingency and weather deviation procedures were introduced. For contingencies, you now turn at least 30 degrees and offset by 5 NM. For weather deviations, you now do your 300ft up/down offset when 5 NM away from track. More info here.


  • PBCS From March 29th 2018, PBCS is a requirement for the daily mandated PBCS NAT Tracks (right now, that the 3 core tracks each day) between FL350-390.  PBCS for the NAT means having both RCP240 (4 minute comms loop) and RSP180 (3 minute position reporting). If you’re missing approval for either, then you can fly anywhere other than along the core NAT tracks FL350-390. Read more about PBCS in our article, and check out the NAT Circle of Change for an easier graphical representation.
  • RLAT  From January 4th 2018, Shanwick and Gander increase the number of RLAT tracks – most tracks between FL350-390 will now be RLAT – 25nm separation between them. RLAT replaced by the term PBCS.


  • SLOP – Offsetting is now mandatory. Choose 0, 1, or 2nm right of track. We think 1 or 2 is best. Consider the recent A380 story.
  • TCAS 7.1: From January 1st, 2017, TCAS 7.1 is required throughout the entire NAT region.
  • Cruising Level: Effective 2017, you no longer need to file an ICAO standard cruising level in NAT airspace.
  • Gross Nav Error: This is now defined as greater than 10nm. Everywhere else in the world, it’s 25nm.
  • Datalink Mandate: Since Dec 2017, datalink now required throughout the NAT Region from FL350-390. Exempt areas: Tango Routes, airspace north of 80N, Surveillance airspace, Blue Spruce routes, and New York OCA.


  • Confirm Assigned Route Introduced August 2016, you will see this message when you enter NAT airspace with datalink, and you should reply with the planned route in NAT airspace. Designed to catch errors.
  • NAT HLA The airspace formerly known as MNPS. Changed February 2016. NAT HLA = NAT High Level Airspace. Now includes Bodo Oceanic, and aircraft must be RNP 4 or RNP10. Previous MNPS approvals good through 2020.


  • RLAT Started December 2015, spacing on the NAT Tracks reduced to “Half Track” (30nm) for 3 core tracks. RLAT=Reduced Lateral Separation Minima. Next phase of this (ie. all NAT Tracks 350-390) was introduced in Dec 2017.
  • SLOP Offsetting right of track by 1nm or 2nm became Mandatory.

July 2021:
We have published a completely updated and even more awesome North Atlantic Plotting & Planning Chart!

This chart is completely new – we started from scratch, expanded the coverage area, and then worked as a group to add all the useful things we could think of that a pilot or dispatcher crossing the North Atlantic might need. Check it out!


More on the topic:

More reading:

Mark Zee

Mark Zee

I am the founder of OPSGROUP, and a former airline pilot, ATCO and flight dispatcher. Based in Christchurch, New Zealand. Question for us? Write to


  • David Mumford says:

    I read the contingency turn-back procedure as follows:
    FIRST turn at least 45 degrees, THEN maintain 10/15nm offset track (depending on whether you can/cannot maintain your assigned flight level), THEN climb or descend to get out of the way of the rest of the NAT traffic (above FL410 or below FL280), THEN maintain a flight level which differs from those normally used (by 1000ft if above FL410, or by 500ft if below FL410)… and then finally once all that’s done you can initiate your turn-back.

  • Steve Thorpe says:

    It is also contained in the NAT OPS Bulletin 2015_003 Revision 4, effective 25 JAN 2017. Section 5.8.

  • Greg L says:

    I have a question related to what Dave H brought up. I found the same section (13.3.5) that FSB included in their reply to Dave H. I understand that it is relevant to RLatSM because it recommends an offset of only 15nm, but it is not specific to a turn-back as it specifies “…while subsequently maintaining a same direction 15 NM offset track…”. So if I am reading it correctly, it is suggesting that you continue in the same direction, but offset 15nm, and then descend/climb as appropriate before making any turn across the OTS or making a turn-back. Am I understanding this correctly?

  • Norm G says:

    Do you have a link to the V.2017? All I can find is V.2016-1. Thanks!

  • FSB says:

    Hi David, yep, the source is the new NAT Doc 007 –

    Page 17: “Modifications to the Contingency Procedures, to take account of possible turn-backs when operating in RLatSM airspace, are included in Chapter 13.”

    13.3.5 Before commencing any diversion across the flow of adjacent traffic or before initiating any turn-back (180°), aircraft should, while subsequently maintaining a same direction 15 NM offset track , expedite climb above or descent below the vast majority of NAT traffic (i.e. to a level above FL410 or below FL280), and then maintain a flight level which differs from those normally used: by 1000 ft if above FL410, or by 500 ft if below FL410. However, if the pilot is unable or unwilling to carry out a major climb or descent, then any diversion or turn-back manoeuvre should be carried out at a level 500 ft different from those in use within the NAT HLA, until a new ATC clearance is obtained.

  • David H says:

    I cannot find a source reference for the “Contingency Procedure: Published January 2017, a new turn-back (180) procedure is introduced – turn back to parallel previous track by 15nm.” Are you able to provide a link? Thx

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