As is the norm in most of the NAT Region, the Reykjavik CTA is free of fixed routes, the only constraints on routing being the use of anchor points at whole degrees of latitude at every whole degrees of longitude for tracks trending West/East and at 5° intervals of latitude for North/South oriented tracks.
A significant portion of the NAT traffic operates on tracks, which vary from day to day dependent on meteorological conditions. The variability of the wind patterns would make a fixed track system unnecessarily penalizing in terms of flight time and consequent fuel usage. Nevertheless, the volume of traffic along the core routes is such that a complete absence of any designated tracks (i.e. a free flow system) would currently be unworkable given the need to maintain procedural separation standards in airspace largely without radar surveillance.
As a result, an OTS is set up on a diurnal basis for each of the Westbound and Eastbound flows. Each core OTS is comprised of a set, typically 4 to 7, of parallel or nearly parallel tracks, positioned in the light of the prevailing winds to suit the traffic flying between Europe and North America.
The designation of an OTS facilitates a high throughput of traffic by ensuring that aircraft on adjacent tracks are separated for the entire oceanic crossing - at the expense of some restriction in the operator's choice of track. In effect, where the preferred track lies within the geographical limits of the OTS, the operator is obliged to choose an OTS track or fly above or below the system. Where the preferred track lies clear of the OTS, the operator is free to fly it by nominating a random track. Trans-Atlantic tracks, therefore, fall into three categories: OTS, Random or Fixed.
The location of the NAT tracks depends on the meteorological conditions and varies from day to day. In 2010, 92.3% of the traffic in the Reykjavik CTA was on random tracks and 7.7% was on the NAT tracks. During 2010, the westbound NAT tracks entered the Reykjavik CTA 111 days while the eastbound NAT tracks entered the Reykjavik CTA only 6 days.