North Atlantic Tracks for the westbound crossing of February 24, 2017, with the new RLAT Tracks shown in blue
The North Atlantic Tracks, officially titled the North Atlantic Organised Track System (NAT-OTS), are a structured set of transatlantic flight routes that stretch from eastern North America to western Europe across the Atlantic Ocean, within the North Atlantic airspace region. They ensure that aircraft are separated over the ocean, where there is little radar coverage. These heavily travelled routes are used by aircraft flying between North America and Europe, operating between the altitudes of 29,000 and 41,000ft (8,800 and 12,500m) inclusive. Entrance and movement along these tracks is controlled by special oceanic control centres to maintain separation between aircraft. The primary purpose of these routes is to allow air traffic control to effectively separate the aircraft. Because of the volume of NAT traffic, allowing aircraft to choose their own co-ordinates would make the ATC task far more complex. They are aligned in such a way as to minimize any head winds and maximize tail winds impact on the aircraft. This results in much more efficiency by reducing fuel burn and flight time. To make such efficiencies possible, the routes are created twice daily to take account of the shifting of the winds aloft and the principal traffic flow, eastward in North America evening and westward twelve hours later.
The first implementation of an organised track system across the North Atlantic was for commercial shipping, dating back to 1898 when the North Atlantic Track Agreement was signed. After World War II, increasing commercial airline traffic across the North Atlantic led to difficulties for ATC in separating aircraft effectively, and so in 1961 the first occasional use of NAT Tracks was made. In 1965, the publication of NAT Tracks became a daily feature, allowing controllers to force traffic onto fixed track structures in order to effectively separate the aircraft by time, altitude, and latitude.[1] In 1966, the two agencies at Shannon and Prestwick merged to become Shanwick, with responsibility out to 30°W longitude.[2]
2019 - ASEPS (Advanced surveillance enhances procedural separation) introduced following introduction of Space Based ADS-B.
Route planning
The specific routing of the tracks is dictated based on a number of factors, the most important being the jetstream—aircraft going from North America to Europe experience tailwinds 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. The North Atlantic Tracks are published by Shanwick Centre (EGGX) and Gander Centre (CZQX), in consultation with other adjacent air traffic control agencies and airlines.[citation needed]
The day prior to the tracks being published, airlines that fly the North Atlantic regularly send a preferred route message (PRM) to Gander and Shanwick. This allows the ATC agency to know what the route preferences are of the bulk of the North Atlantic traffic.
Provision of North Atlantic Track air traffic control
Using a NAT Track, even when they are active in the direction an aircraft is flying, is not mandatory. However, less than optimum altitude assignment, or a reroute, is likely to occur. Therefore, most operators choose to file a flight plan on a NAT Track. The correct method is to file a flight plan with an Oceanic Entry Point (OEP), then the name of the NAT Track, e.g. "NAT A" for NAT Track Alpha, and the Oceanic Exit Point (OXP).[citation needed]
A typical routing would be: DCT KONAN UL607 EVRIN DCT MALOT/M081F350 DCT 53N020W 52N030W NATA JOOPY/N0462F360 N276C TUSKY DCT PLYMM. Oceanic boundary points for the NAT Tracks are along the FIR boundary of Gander on the west side, and Shanwick on the east side.[citation needed]
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 11:30 UTC to 19:00 UTC at 30W) are indicated by the letters A,B,C,D etc. (as far as M if necessary, omitting I), where A is the northernmost track, and eastbound tracks (valid from 01:00 UTC to 08:00 UTC at 30W) are indicated by the letters Z,Y,X,W etc. (as far as N if necessary, omitting O), 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°N latitude, 40°W longitude).[citation needed]
A ‘random route’ must have a waypoint every 10 degrees of longitude. Aircraft can also join an outer track half way along.[citation needed]
Since 2017, aircraft can plan any flight level in the NAT HLA (high level airspace), with no need to follow ICAO standard cruising levels.[3]
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. 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 pilots. It may be that the track is not available at that altitude or time so an alternate track or altitude will be assigned. Aircraft cannot change assigned course or altitude without permission.
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 the 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.
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 ten 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.
Since there is little radar coverage in the middle of the Atlantic, aircraft must report in as they cross various waypoints along each track, their anticipated crossing time of the next waypoint, and the waypoint after that. These reports enable the Oceanic Controllers to maintain separation between aircraft. These reports can be made to dispatchers via a satellite communications link (CPDLC) or via high frequency (HF) radios. In the case of HF reports, each aircraft operates using SELCAL (selective calling). The use of SELCAL allows an aircraft crew to be notified of incoming communications even when the aircraft's radio has been muted. Thus, crew members need not devote their attention to continuous radio listening. If the aircraft is equipped with automatic dependent surveillance, (ADS-C & ADS-B), voice position reports on HF are no longer necessary, as automatic reports are downlinked to the Oceanic Control Centre. In this case, a SELCAL check only has to be performed when entering the oceanic area and with any change in radio frequency to ensure a working backup system for the event of a datalink failure.
Maximizing traffic capacity
Increased aircraft density can be achieved by allowing closer vertical spacing of aircraft through participation in the RVSM program.[citation needed]
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.[citation needed]
On 12 November 2015, a new procedure allowing for reduced lateral separation minima (RLAT) was introduced. RLAT reduces the standard distance between NAT tracks from 60 to 30 nautical miles (69 to 35mi; 111 to 56km), or from one whole degree of latitude to a half degree. This allows more traffic to operate on the most efficient routes, reducing fuel cost. The first RLAT tracks were published in December 2015.
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 typically leave Europe between early morning to late afternoon and arrive in North America from early afternoon to late evening. 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 alternate on the basis of a variety of variable factors, but predominantly due to weather systems.[citation needed]
The FAA, Nav Canada, and NATS publish a NOTAM daily with the routes and flight levels to be used in each direction of travel, available online.[4]
Space-based ADS-B
At the end of March 2019, Nav Canada and the UK's National Air Traffic Services (NATS) activated the Aireon space-based ADS-B relayed every few seconds by 450nmi (830km) high Iridium satellites to air traffic control centers.Aircraft separation can be lowered from 40nmi (74km) longitudinally to 14–17nmi (26–31km), while lateral separations will be reduced from 23 to 19nmi (43 to 35km) in October and to 15nmi (28km) in November 2020. In the three following months, 31,700 flights could fly at their optimum speeds, saving up to 400–650kg (880–1,430lb) of fuel per crossing. Capacity is increased as NATS expects 16% more flights by 2025, while predicting that 10% of traffic will use the Organized Track System in the coming years, down from 38% today[when?].[5]
In 2018, 500,000 flights went through; annual fuel savings are expected around 38,800t (85,500,000lb), and may improve later.[6]
Concorde
Concorde did not travel on the North Atlantic Tracks as it flew between 45,000 and 60,000ft (14,000 and 18,000m), a much higher altitude than subsonic airliners. The weather variations at these altitudes were so minor that Concorde followed the same track each day. These fixed tracks were known as 'Track Sierra Mike' (SM) for westbound flights and 'Track Sierra November' (SN) for eastbounds, with an additional 'Track Sierra Oscar' (SO) used if necessary. An additional route, 'Track Sierra Papa' (SP), was used for seasonal British Airways flights from London Heathrow to/from Barbados.[7][8]
Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for pilots.
In aviation and aviation meteorology, a flight level (FL) is an aircraft's altitude at standard air pressure, expressed in hundreds of feet. The air pressure is computed assuming an International Standard Atmosphere pressure of 1013.25 hPa (29.92 inHg) at sea level, and therefore is not necessarily the same as the aircraft's actual altitude, either above sea level or above ground level.
NATS Holdings, formerly National Air Traffic Services and commonly referred to as NATS, provides en-route air traffic control services to flights within the UK flight information regions and the Shanwick Oceanic Control Area. It also provides air traffic control services to 14 UK airports.
Reduced vertical separation minimum (RVSM) is the reduction, from 2,000 feet to 1,000 feet, of the standard vertical separation required between aircraft flying between flight level 290 (29,000 ft) and flight level 410 (41,000 ft). Expressed in the International System of Units (SI), it is the reduction, from 600 m to 300 m, of required vertical separation of aircraft between altitudes 8,850 and 12,500 m. This reduction in vertical separation minimum therefore increases the number of aircraft that can fly in a particular volume of controlled airspace.
Shanwick is the air traffic control (ATC) name given to the area of international airspace which lies above the northeast part of the Atlantic Ocean.
Nav Canada is a privately run, non-profit corporation that owns and operates Canada's civil air navigation system (ANS). It was established by statute in accordance with the Civil Air Navigation Services Commercialization Act.
Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service Provider prior to departure which indicate the plane's planned route or flight path. Flight plan format is specified in ICAO Doc 4444. They generally include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight, the pilot's information, number of people on board, and information about the aircraft itself. In most countries, flight plans are required for flights under IFR, but may be optional for flying VFR unless crossing international borders. Flight plans are highly recommended, especially when flying over inhospitable areas such as water, as they provide a way of alerting rescuers if the flight is overdue. In the United States and Canada, when an aircraft is crossing the Air Defense Identification Zone (ADIZ), either an IFR or a special type of VFR flight plan called a DVFR flight plan must be filed. For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services. For VFR flights, their only purpose is to provide needed information should search and rescue operations be required, or for use by air traffic control when flying in a "Special Flight Rules Area."
Flight planning is the process of producing a flight plan to describe a proposed aircraft flight. It involves two safety-critical aspects: fuel calculation, to ensure that the aircraft can safely reach the destination, and compliance with air traffic control requirements, to minimise the risk of midair collision. In addition, flight planners normally wish to minimise flight cost through the appropriate choice of route, height, and speed, and by loading the minimum necessary fuel on board. Air Traffic Services (ATS) use the completed flight plan for separation of aircraft in air traffic management services, including tracking and finding lost aircraft, during search and rescue (SAR) missions.
Royal Air Force Prestwick otherwise known as RAF Prestwick, was a RAF unit based at the NATS air traffic control centre, adjacent to Glasgow Prestwick Airport, South Ayrshire, in south west Scotland. The unit was home to the Scottish Air Traffic Control Centre (Military) which provided an air traffic control service to military aircraft operating within its area of responsibility. Prestwick was also home to a Distress and Diversion (D&D) Cell which provided assistance to both military and civil aircraft in an emergency.
In air traffic control, an area control center (ACC), also known as a center or en-route center, is a facility responsible for controlling aircraft flying in the airspace of a given flight information region (FIR) at high altitudes between airport approaches and departures. In the US, such a center is referred to as an air route traffic control center (ARTCC).
Procedural control is a method of providing air traffic control services without the use of radar. It is used in regions of the world, specifically sparsely populated land areas and oceans, where radar coverage is either prohibitively expensive or is simply not feasible. It also may be used at very low-traffic airports, or at other airports at night when the traffic levels may not justify staffing the radar control positions, or as a back-up system in the case of radar failure.
The Future Air Navigation System (FANS) is an avionics system which provides direct data link communication between the pilot and the air traffic controller. The communications include air traffic control clearances, pilot requests and position reporting. In the FANS-B equipped Airbus A320 family aircraft, an Air Traffic Services Unit (ATSU) and a VHF Data Link radio (VDR3) in the avionics rack and two data link control and display units (DCDUs) in the cockpit enable the flight crew to read and answer the controller–pilot data link communications (CPDLC) messages received from the ground.
Controller–pilot data link communications (CPDLC), also referred to as controller pilot data link (CPDL), is a method by which air traffic controllers can communicate with pilots over a datalink system.
Standard instrument departure (SID) routes, also known as departure procedures (DP), are published flight procedures followed by aircraft on an IFR flight plan immediately after takeoff from an airport.
In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to secondary factors, such as wake turbulence. Separation can also apply to terrain, obstacles, and controlled airspace, wherein an aircraft must stay at a minimum distance from a block of airspace; as an example, all aircraft must be approved by the controller who "owns" the airspace before the aircraft is approved to enter that sector.
In aviation, an air traffic service (ATS) is a service which regulates and assists aircraft in real-time to ensure their safe operations. In particular, ATS is to:
Strategic lateral offset procedure (SLOP) is a solution to a byproduct of increased navigation accuracy in aircraft. Because most now use GPS, aircraft track flight routes with extremely high accuracy. As a result, if an error in height occurs, there is a much higher chance of collision. SLOP allows aircraft to offset the centreline of an airway or flight route by a small amount, normally to the right, so that collision with opposite direction aircraft becomes unlikely.
Gander Automated Air Traffic System (GAATS) is a proprietary system of Nav Canada used for the oceanic airspace of the Gander Area Control Centre (ACC).
Automatic Dependent Surveillance–Broadcast (ADS-B) is an aviation surveillance technology and form of Electronic Conspicuity in which an aircraft determines its position via satellite navigation or other sensors and periodically broadcasts its position and other related data, enabling it to be tracked. The information can be received by air traffic control ground-based or satellite-based receivers as a replacement for secondary surveillance radar (SSR). Unlike SSR, ADS-B does not require an interrogation signal from the ground or from other aircraft to activate its transmissions. ADS-B can also receive point-to-point by other nearby equipped "ADS-B In" equipped aircraft to provide traffic situational awareness and support self-separation. ADS-B is "automatic" in that it requires no pilot or external input to trigger its transmissions. It is "dependent" in that it depends on data from the aircraft's navigation system to provide the transmitted data.
Reduced Lateral Separation Minima, is an aeronautical flight term identifying the reduction from standard lateral separation minima between aircraft to a lower amount deemed safe, first introduced on the North Atlantic in December 2015 for the North Atlantic Tracks.
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