First, the big idea: the rules of the air are not universal — Page 96, Lesson 163

Let’s pick this up right where the rules of the air get applied to real flying. I want to walk you through the key principle that governs which rules apply when, and then we’ll move into the two flight rule sets you’ll actually fly under. First, the big idea: the rules of the air are not universal. They depend on where the aircraft is and whose aircraft it is. The excerpt gives you a clear hierarchy. When you’re over a foreign state, your own state’s rules may apply, but only if they don’t conflict with the rules published by the State having jurisdiction over the territory you’re overflying. That’s the first layer: the local state’s rules have priority over your own, as long as you’re within their territory. Now, the exception to that is the high seas. The ICAO Council resolved, when adopting Annex 2 in April 1948 and Amendment 1 in November 1951, that the ICAO Rules apply without exception over the high seas. And here’s the definition you need: High Seas are the areas of sea outside the territorial limits of any State. So over open ocean, no single state has jurisdiction, and ICAO’s rules are the absolute authority. Let me give you the practical summary, because this is exactly how it works in the real world. For a UK registered aircraft over the UK, UK rules apply. For a UK registered aircraft over France, both French and UK rules apply, but French rules have priority. And for a UK registered aircraft over the high seas, ICAO rules apply without exception. One more critical point: do not confuse Rules with Law. The rules of the air are the operational standards; the law is the legal framework that enforces them. They’re related but distinct. Now, let’s move to Section 6.3, which is about the applicable rules for actually operating the aeroplane. The operation of an aeroplane, either in flight or on the movement area of an aerodrome, must be in accordance with the general rules. And when in flight, you operate under one of two sets: the visual flight rules, or VFR, if the aircraft is flown in visual meteorological conditions, which we call VMC; or the instrument flight rules, IFR. Finally, Section 6.4 answers the question: IFR or VFR? Here’s the decision logic. A pilot may elect to fly in accordance with the Instrument Flight Rules even in VMC — and in certain circumstances, the ATS Authority, that’s the Air Traffic Services Authority, may require you to do so. But a pilot must fly in accordance with the IFR in IMC, that is, in instrument meteorological conditions. And if you elect to fly VFR, you must do so only where VMC exist. So the rule is: VFR is optional but only in VMC; IFR is mandatory in IMC and always permitted, even in VMC. That’s the core of it: the hierarchy of which rules apply based on location, and the choice between VFR and IFR based on the meteorological conditions you’re in.