Air Traffic Services — Page 278, Lesson 356

Let’s start with the big picture, because this is the foundation of everything we do in Air Traffic Services. We have Air Traffic Control, which we shorten to ATC. The definition is precise: ATC is the service provided to controlled flights inside controlled airspace, or to aerodrome traffic at controlled aerodromes. So the moment you are a controlled flight, or you are moving around a controlled aerodrome, ATC is the service looking after you. Now, the applicability is where it gets interesting, and you need to remember this exactly. ATC is always provided to IFR traffic inside CAS. Let me unpack that. IFR means Instrument Flight Rules — flying by reference to instruments. CAS means Controlled Airspace. So if you are flying IFR inside controlled airspace, you are guaranteed ATC service, no exceptions. But for VFR flights — Visual Flight Rules, flying by visual reference to the ground — ATC is only provided in classes B, C and D of airspace. That is a specific list, and you must remember it: B, C, and D. Not A, not E, not G. Only B, C, and D. And then there is one more category: all SVFR flights are provided with ATC. SVFR is Special VFR — that is VFR flight conducted within a control zone when the weather is below normal VFR minima, and it requires a specific clearance. So the rule is: IFR in CAS always gets ATC, VFR only in B, C, and D, and every SVFR flight gets ATC. Next, let’s look at the ATS Units. ATS stands for Air Traffic Services, and the units that provide them are split into two families. We have Air Traffic Control Units, which we call ATCUs, and we have Flight Information Centres, which we call FICs. The distinction is clean: the ATS units that provide air traffic control are the ATCUs, and the ones that provide flight information are the FICs. Now, within the ATCU family, we have different specialisations. The ATCU that provides area control — that is, ATC to en route traffic, traffic cruising between airports — is called an Area Control Centre, or ACC. And it is standard practice to prefix the unit with a geographical name. So we say London ACC, for example. That tells you which region it covers. Then we move down to the terminal environment. Within a CTR — that is a Control Zone, the controlled airspace around an aerodrome — the unit providing approach control is the approach control office, and it is usually located in a control tower at an aerodrome. So approach control handles aircraft arriving and departing, sequencing them onto the approach. Now here is a refinement: combined approach control offices exist. These are set up where approach control is provided for multiple aerodromes or multiple CTRs from a single location. The classic example is London Terminal Control Centre, which we shorten to LTCC. That one unit provides approach control for a whole list of airports: Heathrow, Gatwick, Stansted, Luton, London City, Biggin Hill, and Northolt. So one combined office, seven aerodromes. Then we have Aerodrome Control, which is provided by an aerodrome control tower. That is the tower you see at the airport, and it controls the traffic in the immediate vicinity of the aerodrome and on the runways. One more point on the units: within an FIR — that is a Flight Information Region, the large area of airspace — the provision of FIS and the Alerting service may come from the same ATSU. FIS is Flight Information Service, and the Alerting service is the one that notifies rescue and emergency services when an aircraft is in distress or overdue. So the point is, one Air Traffic Services Unit can handle both of those functions within a Flight Information Region. Now let’s talk about Ground Control. This is a specific function, and the responsibility is clear: the ground movement of aircraft and vehicles is the responsibility of the aerodrome controller. That is the person in the tower. However, the provision of services to aircraft moving on the manoeuvring area of an aerodrome, and on the apron, may be delegated to a ground movements controller. Let me define those two areas, because they matter. The manoeuvring area is the part of the aerodrome used for the take-off, landing, and taxiing of aircraft — so runways and taxiways. The apron is the area where aircraft are parked for loading, unloading, refuelling, and boarding — the ramp area. So the ground movements controller can take over the job of guiding aircraft and vehicles on those surfaces. And here is the reason for that delegation, and it is a good one: it is usually done to limit the aerodrome RTF to flight safety messages concerning the take-off and landing of aircraft. RTF is Radiotelephony — the radio frequency. So by handing the ground movement chatter to a separate controller, we keep the main tower frequency clear, so that only the critical messages about take-off and landing are using it. That keeps the frequency from getting clogged up with taxi instructions. And at major aerodromes, the movement of aeroplanes and vehicular traffic on — well, the passage cuts off there, but you can see the pattern: at the big airports, that ground movement function is a dedicated role precisely so the tower frequency stays clean for the flight safety critical messages. Let me show you the structure visually, because it helps to see how these units nest together.