NAT Tracks

The most desirable routes are the minimum time tracks (MTT) from Paris, London and central Europe terminating at New York, Chicago, Atlanta, Montreal and Boston. Generally, an MTT is a great circle track with the most favourable wind, and examination of a chart of the North Atlantic will easily show that most of the routes for the destinations would follow very similar tracks. This again concentrates the traffic such that the majority of the traffic flying across the NAT region will be focused on a few FLs (adjacent to the tropopause) and virtually the same track. The situation is further complicated by the time differences that give rise to the ‘tidal flow’. Generally, people wish to leave Europe in the morning to arrive in North America at about mid day local time. A 7-hour flight to New York departing from London at 9am (0900Z) would arrive at 11am local time (1600Z). (Concorde used to arrive before it had taken off!) For the return, daytime flying is wasteful. A 6-hour flight from Boston to London departing at 10am (1500Z) would land at 9pm London time (2100Z). To overcome this, the majority of flights to Europe from North America depart early in the evening to arrive first thing in the morning. The 6pm (2300Z) Virgin flight from Orlando lands at Gatwick at 7am (0700Z) the next morning. To accommodate all these flights going the same way at approximately the same time, a set of roughly parallel tracks is established with lateral separation based on the MNPS RNP. The FLs allocated to these tracks are RVSM levels and to facilitate yet further utilization of the vertical airspace, the tracks are made effectively ‘one way only’ and both the eastbound and the westbound semi-circular RVSM levels are allocated to the track direction. These tracks are called organized tracks and the overall concept is called the organized track system (OTS). Whilst this appears to be much formalized in concept, the use of the tracks is not mandatory, and an operator may plan any route required. A route that does not comply with the existing OTS is called a ‘random route’, and operators planning random routes are asked to observe certain restrictions. These will be covered later.

OTS Track Designation

To accommodate the ‘tidal’ nature of the transatlantic flow, two OTS are established: the daytime OTS westbound, and the night time OTS eastbound. Each track in the OTS is given an individual identifier or designator. For the daytime OTS the tracks are lettered from “A” for the most northerly at the start point and then sequentially lettered in a southerly direction. For the night time OTS, the most southerly track is “Z” with the next track to the north “Y” etc...

OTS Changeover

At some time of the day the eastbound OTS will be replaced with the westbound OTS and vice versa. Clearly, this has to be organized or chaos would result. If the eastbound OTS finished at 1000Z and the westbound started at 1001Z, it would be perfectly feasible for a flight to join the eastbound OTS at 0959Z at FL 310 and at some point in the flight, conflict with a flight joining the westbound OTS at 1001Z also at FL310 but going the opposite way. To overcome this, the OTS period is defined at 30W (approximately the midpoint for most traffic). An aircraft flying the OTS must plan to cross 30W during the period of the OTS to be able to fly the entire route as a NAT track. This, however, does not totally solve the problem: consider the case of an aircraft crossing 30W at one minute before the end of the OTS! To make it as safe as can be, a changeover (buffer) period is also established which exists from the end of one OTS until the start of the OTS in the reverse direction. This will allow an aircraft crossing 30W at the end of the OTS to complete the route before an aircraft flying the reverse direction would be permitted to join the route.

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The standard OTS periods of validity are;

Daytime (Westbound) OTS 1130-1900UTC at 30W

Night-time (Eastbound) OTS 0100-0800UTC at 30W.

These times occasionally change however, any changes will be highlighted in the remarks of the Track Message.

The changeover periods are 0801Z to 1129Z and 1901Z to 0059Z. Don’t forget, the OTS only exists in the NAT region and flight in the NAT region will only be part of the total journey. For example, British Airways BA289 flies from London to Phoenix where 60% of the flight is outside the NAT area.

OTS Message (Track Message - TM)

At set times each day, the airspace managers of the 5 OCAs together with Met advisers hold a conference to decide the following day’s OTS. As well as considering the weather they will take into account route requests from operators, who can request specified routings by submitting a Preferred Route Message (PRM) in advance. The manager of Shanwick is then responsible for publishing the next daytime (westbound) OTS and the Gander manager publishes the night time (eastbound) OTS. The OTS is then distributed to interested parties (domestic airspace ACCs, operators etc.) in the form of an OTS message which specifies the date; period of validity; the routes (Lat/Long positions and named positions) by designator, and remarks including the track message identifier (TMI) and notices regarding airspace reservations and navigational data.

Track Message Identifier (TMI)

The TMI is a method of identifying the OTS promulgated by the OACC. It consists of the name of the OACC, the abbreviation TMI followed by the Julian date of the OTS. The Julian calendar starts at 001 for 1 January and ends at 365 for 31 December (366 for a leap year). So, the eastbound OTS for 28 February is Gander TMI 059. If any amendment is required, the whole NAT track message will be re-issued. An added note will indicate the revision with an alphabetic character, e.g. TMI059A, then B, etc.

Track Routings

After the track identifier, the first position in a NAT track is the entry point. This can be either a Lat/Long (a 5-character group giving the whole number of degrees of latitude, followed by a slash, then the whole number of degrees longitude e.g. 59/10 meaning 5900N01000W) or a named position (the ICAO standard for position names is used - 5 letters e.g. CIMAT). The rest of the route, in the 5-character lat/long form and named positions if applicable, follows. An example of a westbound route in the TM is as follows:

A 59/10 61/20 61/30 61/40 61/50 60/60 CIMAT

The route is route “A” therefore it is the most northerly of that OTS. The entry point is 59N 10W. From there the route is 61N 20W; 61N 30W; 61N 40W; 61N 50W; 60N 60W and exit at point CIMAT (which is defined in the Montreal CTA as 5930N 06300W).

Allocation of FLs

The next part of the TM for the route is the allocation of FLs. In theory, all the RVSM FLs (290 - 410 inclusive) should be available for allocation. In practice this is not always the case. For the more popular routes more FLs are usually available than for the less popular. Generally, FLs 290 and 300 are too low for normal traffic and FLs 400 and 410 just a touch too high. Also the freeing of RVSM FLs to non-OTS traffic is in keeping with the objective of making as much airspace available for non-NAT Track traffic as possible, and also offers flexibility for random routes. For the westbound OTS track A above, the allocation of FLs was as follows:

EAST LVLS NIL; WEST LVLS 310 320 330 340 350 360 390

The inclusion of EAST LVLS NIL implies that for the period of the OTS all other direction traffic along this route would be random route traffic. Indeed, it is unlikely that contra direction traffic would be accepted into the OTS now because of RVSM, whereas before the introduction of RVSM at least one level was always reserved for contra direction traffic.

Domestic Routes

The TM also includes details of specific routing from domestic airspace to the entry point for the route and also from the exit point into domestic airspace. This will allow domestic airspace managers to ‘flow manage’ transatlantic traffic into the domestic airways or high-level route system within the receiving FIR. For route A the TM included:

EUR RTS WEST NIL; NAR N464B N466B N468B N472B N474B­

This implies that there are no specified European routes to the start point, and from CIMAT the NAR (North American routings) are N464B etc.

Random Routes

As the use of the OTS is not mandatory, operators may plan to use any other route. Such routes are called random routes. Examples of a random route could be: the reciprocal of an OTS track; a track that follows part of an OTS track; a route that crosses 30W outside of the relevant OTS; a track that is completely outside of the OTS or a track that crosses one or more OTS tracks. In any event, operators are required to consider the implications of planning such routes and the OACCs will apply whatever restrictions are necessary to random routes to protect the OTS traffic. The use of the unrestricted FLs (those not included in the TM for each route) would be appropriate. If an operator wishes to plan a route that uses part of the OTS, then the outside routes (most northerly or most southerly) should be planned to be used for the part of the OTS to be flown.

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Figure 9.2: Example of day-time westbound organized track system

Example of a westbound NAT track message:

(NAT-1/2 TRACKS FLS 310/ 390 INCLUSIVE OCTOBER 8/ 1130Z TO OCTOBER 8/ 1900Z PART ONE OF TWO PARTS-

A 59/10 61/20 61/30 61/40 61/50 60/60 CIMAT EAST LVLS NIL

WEST LVLS 310 320 330 340 350 360 390 EUR RTS WEST NIL

NAR N464B N466B N468B N472B N474B

B 58/10 60/20 60/30 60/40 59/50 PRAWN YDP EAST LVLS NIL

WEST LVLS 310 320 330 340 350 360 370 380 390 EUR RTS WEST NIL

NAR N322B N328C N334B N336E N346A N348C N352C N356C N362B-

C 57/10 59/20 59/30 58/40 56/50 SCROD VALIE

EAST LVLS NIL

WEST LVLS 310 320 330 340 350 360 370 380 390

EUR RTS WEST NIL

NAR N242B N248B N250C N252B-

D 56/10 58/20 58/30 57/40 55/50 OYSTR STEAM

EAST LVLS NIL

WEST LVLS 310 320 330 340 350 360 370 380 390

EUR RTS WEST NIL

NAR N224C N228A N230B N232B-

(NAT-2/2 TRACKS FLS 310/390 INCLUSIVE OCTOBER 8/ 1130Z TO OCTOBER 8/ 1800Z PART TWO OF TWO PARTS-

F MASIT 56/20 56/30 55/40 53/50 YAY

EAST LVLS NIL

WEST LVLS 310 320 330 340 350 360 370 380 390

EUR RTS WEST VIA DEVOL

NAR N184B N188B N192B-

G 49/15 48/20 45/30 42/40 38/50 35/60 HENCH

EAST LVLS NIL

WEST LVLS 320 340 360

EUR RTS WEST VIA GUNSO

NAR NIL

REMARKS:

1.TRACK MESSAGE IDENTIFICATION NUMBER IS 281 AND OPERATORS ARE REMINDED TO INCLUDE THE TMI NUMBER AS PART OF THE OCEANIC CLEARANCE READBACK

2.MNPS AIRSPACE EXTENDS FROM FL285 TO FL420. OPERATORS ARE REMINDED THAT SPECIFIC MNPS APPROVAL IS REQUIRED TO FLY IN THIS AIRSPACE. IN ADDITION, RVSM APPROVAL IS REQUIRED TO FLY BETWEEN FL310 AND FL390 INCLUSIVE

3.EIGHTY PERCENT OF GROSS NAVIGATION ERRORS OCCUR AFTER A REROUTE. ALWAYS CARRY OUT WAYPOINT CROSS-CHECKS (END OF PART TWO OF TWO PARTS )

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Example of an eastbound NAT track message:

(NAT-1/1 TRACKS FLS 310/390 INCLUSIVE OCTOBER 9/ 0100Z TO OCTOBER 9/ 0800Z

PART ONE OF ONE PARTS-

W CYMON 51/50 52/40 52/30 52/20 53/15 BURAK

EAST LVLS 310 320 330 340 350 360 370 380 390

WEST LVLS NIL

EUR RTS WEST NIL

NAR N95B N97B-

X YQX 50/50 51/40 51/30 51/20 52/15 DOLIP

EAST LVLS 310 320 330 340 350 360 370 380 390

WEST LVLS NIL

EUR RTS WEST NIL

NAR N79B N83B-

Y VIXUN 49/50 50/40 50/30 50/20 51/15 GIPER

EAST LVLS 310 320 330 340 350 360 370 380 390

WEST LVLS NIL

EUR RTS WEST NIL

NAR N63B N67B-

Z YYT 48/50 49/40 49/30 49/20 50/15 KENUK

EAST LVLS 310 320 330 340 350 360 370 380 390

WEST LVLS NIL

EUR RTS WEST NIL

NAR N53B N55A

REMARKS:

1.CLEARANCE DELIVERY FREQUENCY ASSIGNMENTS FOR AIRCRAFT OPERATING FROM MOATT TO BOBTU INCLUSIVE:

LOACH AND NORTH 128.7 SCROD TO YAY 135.45 DOTTY TO YQX 135.05 VIXUN AND SOUTH 119.425

2.TRACK MESSAGE IDENTIFICATION 282.

REMINDED THAT MNPS APPROVAL IS REQUIRED TO FLY IN THIS AIRSPACE. IN ADDITION, RVSM APPROVAL IS REQUIRED TO FLY WITHIN THE NAT REGION BETWEEN FL310 AND FL390 INCLUSIVE. PLEASE REFER TO CANADIAN NOTAM 980097 OR A3797.

3. 80 PERCENT OF GROSS NAVIGATION ERRORS OCCUR AFTER A REROUTE. ALWAYS CARRY OUT WAYPOINT CROSS-CHECKS. (END OF PART ONE OF ONE PART)

Figure 9.3: Example of night-time eastbound organised track system

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