Reduced Lateral Separation Minimum (RLatSM)

Reduced Lateral Separation Minimum (RLatSM)


Reduced Lateral Separation Minimum (RLatSM) is the implementation of 25nm lateral separation standards in North Atlantic High Level Airspace (HLA) (Minimum Navigation Performance Airspace (MNPS)) for qualified aircraft flying within the Organised Track System (OTS).


Advancements in aircraft avionics, flight management system (FMS) / navigation system accuracy and ATM flight data processing capability fueled an initiative to evaluate if the North Atlantic lateral separation standard of one degree of latitude (nominally 60nm) could be reduced to increase the number of possible route options and thus increase airspace capacity at optimum flight levels. Changes under RLatSM reduce the minimum lateral separation to 25nm, practical achievement of which is accomplished by separating adjacent tracks by one-half-degree of latitude.


RLatSM is being implemented using a phased approach, the first phase of which began in late 2015. Phase 1 introduced one-half-degree spacing by inserting an additional track midway between the two existing core tracks of the NAT Organised Track System (OTS) from flight level (FL) 350 to FL 390 inclusive. Phase 2, when implemented, is anticipated to expand RLatSM throughout the entire NAT OTS.


All RLatSM tracks and FLs will be uniquely identified in Note 3 of the REMARKS section of the OTS Track Message. Only those operators/aircraft eligible for RLatSM operations will be allowed to operate on designated RLatSM tracks between FL 350 and FL 390 (inclusive).

To be eligible to flight plan RLatSM tracks, operators must be:

  • Required Navigation Performance (RNP) 4 approved

and the aircraft must be equipped with both:


Contingency procedures as described in the North Atlantic Operations and Airspace Manual (NAT Doc 007) are unchanged for RLatSM track spacing. Additionally, Strategic Lateral Offset Procedures (SLOP)) are authorised and encouraged.

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