NAT High Level Airspace (HLA) is being modified to safely accommodate more aircraft in tighter airspace, a process that requires additional avionics capability, and the 2018-001 update is the next step towards establishing the new standard. Prior to 29 March, the OTS operated as a hybrid of the old spacing system and the incoming system, aircraft flying on standard tracks with one degree of lateral separation and 10 minutes of longitudinal separation, or on reduced lateral separation minima (RLatSM) tracks, separating them by a half degree laterally and five minutes longitudinally.

Diagram 1  shows standard flight tracks in green and RLatSM tracks in red. The RLatSM were only available at FL350-390 and represented optimised routes. For them to accommodate more traffic, their spacing needs to be reduced, requiring aircraft to have improved communications and surveillance equipment, which for some will mean updated or additional avionics.

The Change & Compliance
From 29 March, new rules, known as Performance Based Communication and Surveillance (PBCS) will manage the NAT HLA OTS. The PBCS system combines and eliminates the use of two older terms, reduced lateral separation (RLat) and reduced longitudinal separation (RLong). The NAT HLA OTS PBCS spacing – which still occurs at FL350-390 – is defined as 23nm of lateral separation and five minutes of longitudinal separation, with 20nm of latitude separation and 50nm of longitudinal separation for New York Oceanic and Santa Maria Oceanic traffic. The existing half-degree latitude separation tracks will become PBCS tracks.