Maximizing Traffic Capacity
Increased aircraft density can be achieved by allowing closer vertical spacing of aircraft through participation in the RVSM program.
Additionally from 10 June 2004 the Strategic Lateral Offset Procedure (SLOP) was introduced to the North Atlantic airspace to reduce the risk of mid-air collision by spreading out aircraft laterally. It reduces the risk of collision for non-normal events such as operational altitude deviation errors and turbulence induced altitude deviations. In essence, the procedure demands that aircraft in North Atlantic airspace fly track centreline or one or two nautical mile offsets to the right of centreline only. However, the choice is left up to the pilot.
The tracks reverse direction twice daily. In the daylight, all traffic on the tracks operates in a westbound flow. At night, the tracks flow eastbound towards Europe. This is done to accommodate traditional airline schedules, with departures from North America to Europe scheduled for departure in the evening thereby allowing passengers to arrive at their destination in the morning. Westbound departures leave Europe mid-day and arrive in North America in the late afternoon. In this manner, a single aircraft can be efficiently utilized by flying to Europe at night and to North America in the day. The tracks are updated daily and their position may alter on the basis of a variety of variable factors, but predominantly due to weather systems.
While the routes change daily, they maintain a series of entrance and exit waypoints which link into the airspace system of North America and Europe. Each route is uniquely identified by a letter of the alphabet. Westbound tracks (valid from 1130GMT to 1900GMT at 30W) are indicated by the letters A,B,C,D etc., where A is the northernmost track, and eastbound tracks (valid from 0100GMT to 0800GMT at 30W) are indicated by the letters Z,Y,X,W etc., where Z is the southernmost track. Waypoints on the route are identified by named waypoints (or "fixes") and by the crossing of degrees of latitude and longitude (such as "54/40", indicating 54° latitude, 40° longitude).
The FAA, Nav Canada, NATS and the JAA publish a NOTAM daily with the routes and flight levels to be used in each direction of travel. The current tracks are available online.
Read more about this topic: North Atlantic Tracks
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