In the USA, the division is lower, at FL180 — Page 256, Lesson 333

Let me walk you through the rest of this airspace picture, because we've just crossed from the FIR into the UIR, and I want to make sure the boundary between them is crystal clear before we go further. The division between the FIR and the UIR is not the same everywhere in the world. In Europe, that dividing line sits at FL195 — that's flight level 195, which is 19,500 feet on the standard pressure setting. In the USA, the division is lower, at FL180. So the same conceptual boundary between the two types of airspace sits at different altitudes depending on which side of the Atlantic you're on. And here's a key point I want you to hold onto: the lower boundary of a UIR will always be a VFR flight level. That's a firm rule — the bottom edge of the upper information region is always defined at a VFR flight level, never anything else. Now let's move into section 14.3, which introduces the open FIR. Think of the FIR as a big container of airspace. Within that container, some parts are carved out and given specific designations — control areas, control zones, restricted airspace, and so on. But whatever is left over — the airspace inside the FIR that is not defined as a CTA, a CTR, or any other 'restricted' airspace — that leftover is called the open FIR. And here's the crucial operational point: within the open FIR, the only air traffic services offered are a Flight Information Service and the Alerting Service. That's it. No control service, no separation service. Just flight information — which is essentially advisory traffic and weather information — and the alerting service, which is the mechanism that gets triggered if an aircraft is in distress or overdue, to alert search and rescue. So if you're flying in the open FIR, you are not being controlled; you're being informed and, if things go wrong, you'll be alerted. Let me show you what this looks like on a chart, because the relationship between the FIR, the CTA, and the CTR is much easier to grasp visually. Now, section 14.4 takes us over the oceans. Over large areas of the world's oceans — the North Atlantic is the classic example — air traffic control faces special problems. The navigation is relatively poor compared to overland, and communications are of necessity done by HF, high frequency radio, which requires the use of radio operators. That's a very different setup from the VHF you'd use closer to shore. To solve these problems, or at least to make them manageable, the airspace above FL55 over the oceans is designated as OCAs — Oceanic Control Areas. So above flight level 55, over the ocean, you're in an OCA, and there strict rules are enforced and special navigation procedures are applied. The whole point of the OCA is to impose order on an environment where the normal tools of control are weaker. Finally, section 14.5 covers Prohibited, Restricted, and Danger Areas. All of these — every Prohibited, Restricted, and Danger Area within a state — are contained within the FIR or FIRs of that state. And they're all subject to notification of activity and change in status by NOTAM. A NOTAM is a notice to airmen — it's the formal way that changes to the status of these areas get broadcast to pilots. Each area gets an individual designator, and the designator has a specific structure: the country identifier, then the letter P, R, or D, followed by a number in the range 001 to 999. P stands for Prohibited, R for Restricted, D for Danger. Let me give you the example from the text: in the UK, a danger area off the north coast of Cornwall is designated EG D001. EG is the ICAO identifier for the UK. D tells you it's a danger area. And 001 is the unique number for that particular area. So every one of these areas in the world has a unique code that tells you which country it's in, what kind of area it is, and which specific area it is. That's the complete picture of these airspace classifications — the UIR boundary, the open FIR with its limited services, the oceanic control areas, and the prohibited, restricted, and danger areas with their NOTAM-driven status and their designator system.