North Atlantic Ops – Trial Implementation of Reduced Lateral Separation Minimum

PT 3 M minute read
North Atlantic Ops – Trial Implementation of Reduced Lateral Separation Minimum

Evolution in aircraft avionics and air traffic flight data processing has driven an initiative to reduce current lateral separation minima over the North Atlantic. A Reduced Lateral Separation Minimum (RLatSM) trial program goes into effect November 12, 2015, on the North Atlantic Tracks (NATs). General Aviation (GA) operators have the opportunity to participate in the trial.

The following is an overview of what you need to know:

1. Objective

Advances in onboard Performance-Based Navigation (PBN) capabilities have made it possible to consider reducing lateral separation within the NATs. The goal is to increase capacity on optimal flight routings over the North Atlantic. Long-term benefits include the potential to greatly expand the number of available NATs and boost capacity on preferred routings/optimal Flight Levels (FLs).

2. Proposed changes

Lateral separation on the NATs is currently one degree, or 60 Nautical Miles (NM). The RLatSM trial program reduces separation to half a degree. The initial phase of this was the Controller Pilot Data Link Communications (CPDLC) requirements that were implemented earlier within the NATs. On CPDLC-designated routes, specific onboard equipment is necessary in order to operate between FL 360 and 390 on certain airways. Today, it’s still possible to operate outside FL 360-390 CPDLC airways if an operator is not CPDLC-equipped. But, eventually, it’s anticipated that all operators may need to be CPDLC-equipped to fly airways at all FLs within the NATs.

3. Trial phase impacts only certain NATs

The RLatSM trial phase commences with trial lateral separation of 25 NM on portions of the Gander, Shanwick, and Reykjavik Oceanic Control Areas (OCAs). Length of the phase trial period is unknown at this time. Once the initial trial phase has been completed, we anticipate that RLatSM rules will eventually cover the entire NAT OCA airspace.

4. RLatSM implementation

RLatSM will be implemented using a phased approach. Phase 1 introduces half degree spacing between core tracks of the NAT-Organized Track System (OTS), from FL 350 to 390 inclusive. Phase 2 will expand implementation of reduced spacing throughout the entire NAT OTS. Later, Phase

3 will encompass the entire International Civil Aviation Organization (ICAO) NAT region, including converging and intersecting track situations. While dates of implementation of Phase 2 and 3 are still unknown, it’s anticipated that Phase 2 may go into effect six to nine months after commencement of the Phase 1 period. The goal is to have the entire North Atlantic region operating on PBN and CPDLC by 2020.

5. RLatSM considerations

During Phase 1 of the trial, GA operators have the opportunity to take advantage of 25 NM lateral separation on center core NATs, where CPDLC is currently required. Operator requirements for participation in the trial include:

  • Minimum navigation performance
  • Minimum Navigation Performance Specification (MNPS)-approved
  • RNP4-approved
  • equipped for Automated Dependent Surveillance-Contact (ADS-C)
  • equipped for CPDLC

6. Participation in the trial

Operators do not need to apply to participate in Phase 1 of the RLatSM trial. During the time they’re cleared for NAT operations, they may be offered routings with reduced lateral separation, based on PBN equipment listed in section 18 of their ICAO flight plans. Be mindful that flight communications, navigation, and surveillance (CNS) systems must remain operational during flight and crew are required to report any failure or malfunction of GPS, ADS-C, or CPDLC to ATC.

7. PBN considerations

To participate in Phase 1 of the trial, operators will be using different equipment – including CPDLC and FANs 1/A. When there’s an issue with this onboard reporting technology, operators must be ready and prepared to go back to voice communications.

8. Flight planning requirements

In order to participate in the RLatSM trial, operators need to note specific information in the ICAO section of their flight plan:

  • Field 10a (Radio communication, navigation and approach aid equipment and capabilities);
    • Insert “J5” to indicate CPDLC FANS1/A SATCOM (Inmarsat) and/or “J7” to indicate CPDLC FANS1/A SATCOM (Iridium) data link equipment; and
    • Insert “X” to indicate MNPS operational approval;
  • Field 10b (Surveillance equipment and capabilities);
    • Insert “D1” to indicate ADS with FANS 1/A capabilities;
  • Field 18 (Other Information);
    • Insert the characters “PBN/” followed by “L1” for RNP4

9. More information is available

Documents regarding RLatSM can be found on ICAO’s website. ICAO document 007 also provides information regarding these changes in the North Atlantic region. Additional information on the trial phase can also be found on NavCanada’s Aeronautical Information Circular 31/14.


In the future once reduced lateral separation over the NAT becomes permanent, GA operators will need to have appropriate PBN equipment/letters of authorization, or they’ll face restrictions and difficulty in transitioning through this airspace. For the time being, 3rd-party providers are able to assist operators in handling changing RLatSM flight planning requirements. Over the long term, however, operators will need to ensure they have appropriate and mandated PBN equipment in place to fly any NAT routings/FLs over the North Atlantic region.


If you have any questions about this article or would like assistance with any flight planning needs, contact me at

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