Originally Posted by
Busdriver01
As I understand it, the requirement / need to IDENT has to do with what sort of handover between tower and departure has occurred?
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..