When there are several airports close to each other, a single ATC, formally known as Terminal Control Center may service all airports. The airspace boundaries and altitudes assigned to a Terminal Control Center, which vary widely from airport to airport, are based on factors such as traffic flows, neighboring airports and terrain. [London Terminal Control Centre][1] is an example of a large and complex Terminal Control Center. Its service area is up to 20,000 feet and out to 100 nautical miles. It controls: - six London airports - one Royal Air Force station - provides en-route services to other aircraft that entered its airspace Another example can be found with [Berlin-Tegel][2] and [Berlin-Schönefeld][3], which have adjacent control zones that share a common boundary west to east and have an overlaying class C TMA airspace up to FL100. Both airports share the same TMA controller/approach sector:<br>`BREMEN RADAR Approach: 119.62` ![CTR Area Berlin][4]<br><sub>_Image Source: www.skyvector.com_</sub> --- FAA is implementing a new airspace system which will increase efficiencies at metropolitan areas with complex air traffic flows. This system, known as [Next Generation Air Transportation System][5] is introducing the concept of a [metroplex][6]: > In FAA parlance, metroplex refers to a system of airports in close > proximity and their shared airspace that serve one or more major > cities. A metroplex has at least one, but often two or more major > commercial airports. [1]: http://en.wikipedia.org/wiki/London_Terminal_Control_Centre [2]: http://skyvector.com/airport/EDDT/Berlin-Tegel-Airport [3]: http://skyvector.com/airport/EDDB/Berlin-Schonefeld-Airport [4]: https://i.sstatic.net/ZTPAc.png [5]: http://en.wikipedia.org/wiki/Next_Generation_Air_Transportation_System [6]: https://www.faa.gov/nextgen/snapshots/metroplexes/