Airspace — Page 266, Lesson 337

Let’s pick up with the upper reaches of controlled airspace, because that’s where this part of the chapter starts. 14.9 — Upper Control Areas. When a Control Area, a CTA, extends above Flight Level 195 — that’s FL195, roughly 19,500 feet on the standard pressure setting — the rules that apply to it may be the rules of the lower airspace. So even though you’re physically high up, the regulatory treatment can stay with the lower-airspace rules. That’s the key point: altitude alone doesn’t automatically change the rule set; it depends on how the airspace is designated. 14.10 — Control Units. Now, who actually provides the air traffic control? The provision of ATC to flights in Controlled Airspace, CAS, is the responsibility of the air traffic control units — abbreviated ATCUs — within the designated airspace. So the unit is tied to the airspace, not just to the aircraft. There are three types you need to know. Area Control Centres provide ATC within CTAs — that’s the en-route, wide-area control. Approach Control Units and Aerodrome Control Towers provide the service required in CTRs — Control Zones, the airspace around aerodromes. So: Area Control Centres for the big Control Areas, Approach and Tower for the Control Zones. 14.11 — Classes of Airspace: Introduction. Here’s the big picture. In 1980, ICAO introduced a uniform system of classification of airspace, to replace the disparate systems of airspace reservations that existed around the world. Before that, different states did their own thing. The ICAO system classifies airspace into 7 categories, from A to G. Each class is defined by four things: the rules applicable, the ATC service provided, the separation standards applicable, and the utilization of the airspace. So when you see a class letter, you’re really reading a package deal of those four factors. 14.12 — Controlled Airspace (CAS). Classes A through E are classified as controlled airspace. Within CAS, air traffic control is provided to controlled flights. Now, an important rule: in these classes, IFR flights are always controlled flights — IFR, Instrument Flight Rules. In classes A and B, all permitted flights are controlled — so even VFR traffic is controlled there. But in classes C and D, ATC is provided to VFR traffic only when it conflicts with IFR traffic. So the level of service to VFR depends on the class. CAS itself is defined as CTAs — including airways — and CTRs. And one more specific point: ICAO states that class E airspace cannot be used as a CTR. So a Control Zone can never be class E. 14.13 — Advisory Airspace. Class F is defined as advisory airspace. Here, advisory ATC is provided to IFR traffic which requests the service — that’s called participating traffic. So it’s voluntary. All IFR traffic flying in class F airspace is required to file a flight plan — a FP — but no ATC clearance will be issued. The service is limited to the provision of advice and information, and only participating flights are separated. And finally, class F airspace is considered to be temporary — it’s established for a limited purpose, not a permanent structure. Let me show you how these classes sit together visually. So the takeaway: A through E are controlled, F is advisory and temporary, and the class letter tells you the rules, the service, the separation, and the usage.