Originally Posted by SM4 Pirate
Mostly it's a coordination event. Not necessarily about you, but someone else in my airspace or coming into it, or maybe someone 'skimming my airspace' that I need an Ident or boundary traffic on. Everytime you depart somewhere with a frequency transfer within a few minutes; ie EA WOL-ML flight; the coordination is from SY Radar, to SY Deps, to MEL Sectors to NWA Approach; all before the aircraft has hopefully set-course. This might be as quick as 1 minute after the airborne call. Otherwise it's a standard call to the next unit about you coming; ie TWR to DEP, confirming departure instructions, subject to auto release procs.
Other units that coord to us include Flows, Supervisors, technicians, Flightwatch, towers 'under our airspace', international units.
Coord outways R/T by about 5 to one; particularly sequencing and TMA sectors, ie I'm going to do this with my Arriving aircraft, you do this with your departing one (APP-DEP coord) if you've got two or three APP units and DEP units and directors within the TMA etc. it's even uglier.
In non-radar environments, the system (Eurocat, which was designed for no surveillance) does a lot of the coord, but not all of it.
To help us out our comms system is digital now, so your analogue TXs are converted to a digital signal, which nicely takes pitch and volume changes and flattens them, so you sound very similar no matter how you scream; this on top of a coord event is often unreadable; as that sound the same too; we often just finnish the coord and ask you to say again, cause we can 'control' the air for 3 seconds by not answering you, but the chance of the other ATC have someone call is high if you ring them back instead of finnishing it off.
It doesn't always work that way, but we after a while have a really good feel for important calls and ones that can be repeated in a few seconds, even if you don't want to 'say again'.