[Disclaimer. To resolve differences on understanding, documentation and maps or charts shown in IVAO and Skyvector prevails!!]
I had noticed some amount of uncertainty in different people wanting to offer service of ATC this Fall, and seeing "as trouble" to coordinate with multiple ATCs in compact situations. Think... London.
I have been sayin' many times already that the problem is a lack of understanding of airspaces and control zones. Tipically, the control zones of ATC A and B are non-overlaping areas, and hand over of pilots should occurs very smoothly on the zones of airspace change.
BUT this does require every person involved to understand EXACTLY what is the position they are offering, and where their control zone ends, and where the pilot must be transferred to the following controller. Most interesting, per example, complex small areas in the UK can be further subdivided, but we will talk about this on subsequent posts.
For NOW
The Basics
In UK, the airspace is divided in Area Control (the upper zone - traffic en route), the Terminal Control (the traffic on transit), and the Airport control zones (or APP/TWR/GND).
Now, this is where it gets interesting. All charts are seen are a Top-down depiction of the airspace (as seen from above). and they look like a maze of rectangles within rectangles to the untrained eye!. Something like this (and with no colors!!!)
The Airport control zones are smaller rectangles enclosing ONLY manned airports. Then they are surrounded by a tipically weirdly shaped polygon which is the Terminal area control. Which itself is either enclosed or overlapped by yet another set of shapes, which are the Area controls zones.
Those charts depict the lateral boundaries of areas at the same level (tower to tower, or area to area) very accurately, but some three-dimensional thinking begins to be necessary to understand the boundaries of contiguous zones of different levels. The charts use the nomenclature that look like this: (HIGH | LOW) to indicate the elevation profiles on a given point. As in (3500 ft | SFC) to indicate that such zone ends control at 3500 ft.
So, after looking such situation in the image above, and looking now laterally (from the side) instead of top down, this is the picture that must emerge:
In such image we can see clearly when a pilot exits or enter different zones vertically, but we've got no clue on the lateral navigation limits.
I hope
That from the image above the first thing that must come clear is that
a pilot DOES NOT automatically enter your airspace just because he is within 100 nm of your location (nor any agreed upon radius!). Most importantly, at a give altitude, a plane can be exactly on top of your airport, and still NOT in your airspace, but indeed belonging to the control roster of a neighbor ATC fellow. (like, per example, your Area Controller!)
