North Atlantic Tracks
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North Atlantic Tracks are trans-Atlantic routes that stretch from the northeast of North America to western Europe across the Atlantic Ocean. These heavily-traveled routes are used by aircraft from North America travelling to/from Europe. They are used by aircraft flying between the altitudes of 31,000 and 40,000 feet, inclusive. The tracks reverse direction twice daily. During daylight hours all traffic on the tracks operates in a westbound flow. Conversely 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. Conversely, westbound departures leave Europe mid-day and arrive in North America in the late afternoon. In this manner, a single aircraft can be heavily 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.
Concorde did not travel on the North Atlantic Tracks as it flew to the United States from England and France as it flew much higher in altitude, between 45,000ft and 60,000ft. The weather variations at these altitudes were so minor that Concorde followed the same route each day, travelling to and from Europe to North America on fixed tracks. These fixed tracks were known as 'Track Sierra Mike' and 'track Sierra Oscar' for westbound flights and 'Track Sierra November' for eastbounds. An additional route, 'Track Sierra Papa', was used for seasonal British Airways flights from London Heathrow to/from Bermuda.
The specific routing of the tracks are dictated based on a number of factors, the most important being the jetstream - aircraft going to North America from Europe experience headwinds caused by the jetstream. Tracks to Europe use the jetstream to their advantage by routing along the strongest tailwinds. Because of the difference in ground speed caused by the jetstream, westbound flights tend to be longer in duration than their eastbound counterparts. North Atlantic Tracks are published by Shanwick Center (EGGX) and Gander Center (CZQX) in consultation with other adjacent air traffic control agencies and airlines.
Prior to departure, airline flight dispatchers/flight operations officers will determine the best track based on destination, aircraft weight, aircraft type, prevailing winds and Air Traffic Control route charges. Once airborne, the Atlantic Track portion of the flight plan will be confirmed. The aircraft will then contact the Oceanic Center controller before entering oceanic airspace and request the track giving the estimated time of arrival at the entry point. The Oceanic Controllers then calculate the required separation distances between aircraft and issue clearances to the pilot. It maybe that the track is not available at that altitude or time so the pilots request an alternate track or altitude. Increased aircraft density can be achieved by allowing closer vertical spacing of aircraft through participation in the RVSM program.
The tracks are carefully monitored to ensure that all aircraft follow the track assigned and the proscribed speed and altitude. Despite advances in navigation technology, such as GPS and LNAV, errors can and do occur. While typically not dangerous, two aircraft can violate separation requirements. On a busy day, aircraft are spaced approximately 10 minutes apart. With the introduction of TCAS, aircraft traveling along these tracks can monitor the relative position of other aircraft thereby increasing the safety of all track users.
Contingency plans exist within the North Atlantic Track system to account for any operational issues that occur. For example, if an aircraft can no longer maintain the speed or altitude it was assigned, the aircraft can move off the track route and fly parallel to its track, but well away from other aircraft. Also, pilots on North Atlantic Tracks are required to inform air traffic control of any deviations in altitude or speed necessitated by avoiding weather, such as thunderstorms or turbulence.
Because much of the flying occurs outside radar coverage, aircraft are required to comply with non-radar reporting requirements. In this case, aircraft report their crossing of the route waypoints, their anticipated crossing time of the next waypoint, and the waypoint after that. These reports can be made to dispatchers via a satellite communications link or via High Frequency (HF) radios. In the case of HF reports, each aircraft operates using SELCAL (Selective Calling). This unique code opens up the squelch on the HF radio when received by the unit, allowing pilots to hear only the radio calls for their aircraft.
While the route changes 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 are indicated with a letter from the start of the alphabet (A, B, C, D, E) and eastbound tracks with a letter from the end (S, T, U, V, W, X, Y). 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 (UK) and JAA publish a NOTAM daily with the routes and altitudes to be used in each direction of travel. The current tracks are available online.
