So there are periods during the day when no OTS is active — Page 130, Lesson 202

I want to walk you through the North Atlantic MNPSA — the Minimum Navigation Performance Specification Airspace — and specifically how the Organised Track System, or OTS, works day to day. Let’s start with the standard periods of validity for the OTS. There are two main streams: a daytime westbound OTS, valid from 1130 to 1900 UTC at 30 degrees west, and a night-time eastbound OTS, valid from 0100 to 0800 UTC at 30 degrees west. Those times can change occasionally, and if they do, the change will be highlighted in the remarks section of the Track Message. The changeover periods — the gaps between the two OTS windows — are 0801Z to 1129Z and 1901Z to 0059Z. So there are periods during the day when no OTS is active. Now, it’s important to remember that the OTS only exists in the NAT region — the North Atlantic. Your flight through the NAT region will only be part of the total journey. For example, British Airways flight BA289 from London to Phoenix has about 60% of its flight outside the NAT area. So you plan the OTS portion separately from the rest of the route. OTS Message — also called the Track Message, or TM At set times each day, the airspace managers from the five Oceanic Control Areas — the OCAs — together with meteorological advisers, hold a conference to decide the following day’s OTS. They consider the weather, and they also take into account route requests from operators. Operators can request specific routings in advance by submitting a Preferred Route Message, or PRM. Then the manager of Shanwick is 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 — that includes domestic airspace Area Control Centres, operators, and so on — in the form of an OTS message. That message specifies the date, the period of validity, the routes themselves with their lat/long positions and named positions by designator, and remarks. The remarks include the Track Message Identifier, or TMI, and notices regarding airspace reservations and navigational data. Track Message Identifier — TMI The TMI is a method of identifying the OTS that has been promulgated by the OACC — the Oceanic Area Control Centre. 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, or 366 for a leap year. So, for example, the eastbound OTS for 28 February would be Gander TMI 059. If any amendment is required, the whole NAT track message is re-issued. An added note will indicate the revision with an alphabetic character — so TMI059A, then B, and so on. Track Routings After the track identifier, the first position in a NAT track is the entry point. That entry point can be either a lat/long coordinate or a named position. A lat/long is given as a five-character group: the whole number of degrees of latitude, followed by a slash, then the whole number of degrees longitude. For example, 59/10 means 5900 North, 01000 West. A named position uses the ICAO standard of five letters — for example, CIMAT. The rest of the route follows, in the five-character lat/long form and named positions if applicable. Let me give you an example of a westbound route as it appears in the Track Message: A 59/10 61/20 61/30 61/40 61/50 60/60 CIMAT Route “A” is the most northerly route of that OTS. The entry point is 59 North, 10 West. From there the route goes to 61 North, 20 West; then 61 North, 30 West; 61 North, 40 West; 61 North, 50 West; 60 North, 60 West; and the exit point is CIMAT, which is defined in the Montreal CTA as 5930 North, 06300 West. So when you receive a Track Message, you’ll see the route designator letter, then the sequence of waypoints in that five-character lat/long format or named positions, and that tells you exactly the path you’ll fly across the North Atlantic.