The North Atlantic region is one of the busiest in the world in terms of air-traffic density, with around 1000 flights flying over it everyday (NavCanada, 2011). The North Atlantic Track System (NATS) has been set up by ICAO in order to cope with this. This article provides an overview of NATS.
Definition of North Atlantic Tracks System (NATS)
The North Atlantic Tracks System (NATS) is the principal system of routes between Europe and North America. The exact location of the track changes daily according to weather and traffic demands. In order to deal with the high traffic, the entire area has been designated as MNPS (Minimum Navigation Performance Specifications) airspace, i.e. A/C must be equipped and maintained so as to be continuously capable of a specific level of navigation accuracy.
The NATS/MNPS airspace extends vertically from FL285 to FL420, with the normally used cruising levels lying from FL290 to FL410. This area also happens to be RVSM airspace. The airspace is divided into 5 seperate Oceanic Control Areas, namely Reykjavik, Gander, Shanwick, New York and Santa Maria. The lateral boundaries are shown below:
|Image Source - http://www.tc.gc.ca/media/images/ca-publications/rac11-20-2.gif|
MNPS Seperation Minima
The following table indicates the seperation required between A/C in NATS/MNPS airspace:
|Lateral Separation||5 to 6 times the RNP value, which translates to 50-60 NM in the North Atlantic|
|Longitudinal Separation||Using the Mach-Number technique, the separation should be between 5-10 min|
|Vertical Separation||1000 ft. in RVSM airspace and 2000 ft. in non-RVSM airspace|
Requirements for NATS/MNPS Operations
The following requirements need to be fulfilled in order to operate in NATS/MNPS airspace:
- The A/C should be capable of Class 2 Navigation, which is any en route flight operation or portions of an en route operation which take place outside or beyond the designated Operational Service Volume of ICAO standard airway navigation facilities like VOR, VOR/DME, NDB etc.
- State approval must be given for the navigation equipment and procedures used, including the installation and maintenance procedures, and trainig requirements stipulated by the state should be met.
- The following equipment must be present in all A/C:
- 2 fully operational long range navigation systems that meet NATS/MNPS requirements, e.g. INS, IRU, GPS etc. With just one long range navigation system, the A/C will have to fly a special route known as a "Blue Spruce Route", which are always available in the same place and do not change positions like the tracks on NATS.
- 2 fully serviceable independent primary altimeter systems
- 1 automatic altitude-control system
- 1 altitude-alerting device
- 1 emergency locator transmitter
- At least 1 UTC synchronized A/C clock
Non-MNPS approved A/C can also enter NATS/MNPS airspace provided:
- The climb and descent can be conducted within a range of selected VOR/DME's or NDB's and/or within radar coverage
- Direct pilot/controller communications can be maintained
- Approved A/C are not penalized by these operations
Non-RVSM A/C are also allowed in the airspace, provided:
- Climb or descent through RVSM altitudes is subject to traffic
- RVSM levels are only operated by them for delivery flights, humanitarian flights or ferry flights for maintenance purposes
- Prior approval of an altitude reservation is made
In case of equipment failure, A/C are requested to
- Fix the equipment before departure or land as soon as possible to get it fixed
- Operate at or below FL270 or at or above FL430
- Use Blue Spruce Routes
- Have serviceable VOR, DME and ADF indicators
The Organised Track System
Much of the traffic in the North Atlantic flows in 2 directions, Westbound from Europe (in the morning) and Eastbound from North America (at night), with peak timings occuring between 1130Z and 1800Z for westbound traffic and between 0100Z and 0800Z for eastbound traffic. In order to maintain efficient flow of traffic in the region, the Organised Track System (OTS) has been created by ICAO, which assigns a specific track for each flight in the region.
The location of the tracks vary everyday, and are seldom identical due to weather and operational reasons. Examples of OTS tracks are given below:
Daytime westbound tracks are identified by the letter A. The next most southerly track is labelled B, and so on and so forth.
Night-time eastbound tracks are identified by the letter Z, which is the southern most track at its point of origin. Track Y is the next most northerly track, and so on and so forth.
OTS is not mandatory. A/C can fly random routes that remain clear of the OTS, or join/leave the OTS tracks by any route, but this is subject to ATC approval.
Messages are sent via AFTN (Aeronautical Fixed Telecommunications Network) to all concerned internet addresses, including those of A/C operators and related ATCs, once a track is issued by the OACCs (Oceanic Area Control Centers). These track messages give full details of the co-ordinates of the tracks, along with their flight level. Each track message has a Track Message Identification (TMI) number, which is equivalent to the Julian Calendar date on which the OTS is effective. For example, Feb. 1 is day 32, so the OTS will be identified by TMI 32. If amended, the letter A is appended to it.
Daytime OTS is valid from 1130z to 1800z, whilst night time OTS is valid from 0100z to 0800z. The periods in between are known as transition periods, used to implement a smooth transition between daytime and night-time OTS. During these periods, restrictions are placed to flight planned routes and levels.
Transition routes are used to change-over from the NATS to the domestic airspace in North America and Europe. This is done through systems such as the North American Routes system (NAR) and the North atlantic European Routing Scheme (NERS).
The North American Routes System (NARS) consists of a numbered series of pre-determined routes designed to accommodate major airports in North America.