Originally Posted by
chevvron
A controller can identify a departing aircraft via a known airborne time as an alternative to an ident squawk but this must be done within a fixed distance from the end of the runway so at busier units it may not be possible to use this method.
Used to be done using an 'on channel' intercom (ie the tower controller selects the frequency of the departure controller and tells them of the departure without transmitting it on RTF) but nowadays this procedure seems to have been phased out in favour of making a telephone call or the tower controller just transferring the aircraft to departures and the departure controller requesting the ident..
Just out of interest: its almost exclusively used in the UK - is the UKs radar environment so much different from the others ? Never had to squawk ident out of Amsterdam or Frankfurt or other real busy airports. Or is it just one of these things that always had been done ? Should not Mode S give you all the required info ?