All the entry points to the OTS are within 250 nautical miles of the coast — Page 138, Lesson 216

I want to walk you through the process of obtaining an oceanic clearance for the North Atlantic Tracks — the OTS. Let's start with the entry points. All the entry points to the OTS are within 250 nautical miles of the coast. That means the aircraft should be able to obtain the clearance by VHF radio. Within the states concerned — the countries bordering the North Atlantic — the Oceanic Area Control Centres, or OACCs, have remote VHF transmitter sites on discrete frequencies specifically for this purpose. So you have a dedicated VHF frequency to call for your clearance. If direct VHF communications are not possible, you can use HF radio through the air-ground station. Alternatively, you could make the request through the domestic Area Control Centre, the domestic ACC, on the airways or Upper Information Region frequency that you're already using. And recent advances in technology have made data link available for use with ATC, so that is another possible source of obtaining the clearance. Now, there's an important time-based rule. If the aerodrome of departure is less than 40 minutes flying time from the entry point to the OTS, the oceanic clearance will have to be obtained on the ground — before you even take off. Where this is normal procedure, the OACC has a local transmitter site close by. Examples given are Dublin, Shannon, and Prestwick. Let's look at what the clearance itself contains. The clearance will include: the limit of clearance, which is normally the destination; the track identifier; the entry point; the initial flight level; the Mach number required; and any specific instructions. All of this must be read back by the pilot. However, an abbreviated read-back is permitted. Instead of reading back the full route details, you can replace the route details with the track identifier plus the TMI. The TMI stands for Track Message Identifier — it's a number that identifies the specific set of tracks in use for that OTS period. By reading back the track identifier and the TMI, you indicate to the controller that you have the route details in accordance with the Track Message for the current OTS. If the pilot does not include the track identifier and TMI in the read-back, then the OACC will read the route details, and the pilot will have to read that back fully. So the abbreviated read-back is a time-saver, but only if you use it correctly. There's a specific error term I want you to know. Any misunderstanding concerning clearances and re-clearances that is not picked up by the OACC is known as 'an ATC loop error'. That's a loop — as in the communication loop — where both sides think they understand each other but they don't, and the controller fails to catch the mistake. Finally, the excerpt begins to introduce a condition: if an aircraft encounters, whilst en route to the NAT Oceanic Airspace, a critical in-flight equipment failure, or at dispatch is unable to meet the Minimum Equipment List requirements for RVSM or MNPS — Reduced Vertical Separation Minima and Minimum Navigation Performance Specifications — there are consequences that the next part of the text will cover. But that's where this excerpt ends.