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Chris Kjelgaard explores how air traffic management surveillance of North Atlantic tracks should soon be possible.
Today, once they are more than about 250 miles from land and beyond the range of ground-based radars and Automatic Dependent Surveillance – Broadcast (ADS-B) ground stations, aircraft travelling west or east over the North Atlantic have to be separated by procedural air traffic management (ATM) rules, to ensure safe flight.
These procedural rules rely on separating aircraft travelling in the same direction and on the same tracks by distance. Sufficient procedural separation must be guaranteed in at least the longitudinal direction (usually described as ‘miles in trail’ or measured in minutes) but, often, separation by longitudinal, latitudinal and vertical distance is employed.
Aircraft travelling in opposite directions must be separated by at least 1,000 feet of vertical distance and procedural latitudinal separation is also employed.
Thanks to improvements in aircraft navigation systems to Minimum Navigation Performance Specification standards, procedural separation on the longitudinal axis on each track in the North Atlantic Organised Track System (NAT-OTS) was reduced to five minutes in 2011.
In November 2015, new Reduced Lateral Separation Minima tracks were introduced into the NAT-OTS system (they become effective this month). Each RlatSM track is only one-half degree (30nm) of latitude away from each pair of core westbound tracks and each pair of core eastbound tracks.
But within the next two years, thanks to cooperation between Nav Canada and the UK’s National Air Traffic Services (NATS) and a new technology called space-based ADS-B, active ATM surveillance should replace procedural separation entirely on all NAT-OTS tracks.
This will potentially allow reduced separation of aircraft travelling on busy North Atlantic tracks, while still ensuring safe flight.