Originally Posted by chevvron
In both cases, the pilot must be informed he is identified and the type of ATS being provided must be agreed between pilot and controller.
Specifying the type of ATS being provided and agreeing a 'contract' between pilot and controller is not a universal procedure. In many environments - where ICAO SARPs are applied without modification or creative interpretation - if the aircraft is in CAS it gets controlled, if outside it does not get an ATC service and, in broad terms, will get a (ICAO style) FIS. In such circumstances "Idenitfied [position]" normally suffices and, by definition, it wll be a radar control service.
As to malecontrol's original question, it may be important to clarify what the 'aerodrome radar' is. If it is a 'proper' surveillance radar used to provide approach radar control services, "radar contact lost" would seem fine annd in common use although ICAO specifies "identification lost [reasons] (instructions)" in association with the termination of radar service (Doc 4444 para 12.4.1.10). If the target is thought likely to reappear after recycling the tx'der then "recycle the transponder" will work fine, but again, ICAO specifies the slightly different "reset squawk [(mode)] (code)]" (Doc 4444 para 12.4.3.3). Whether this is sufficient for the controller to say the target is again identified may depend on other circumstances - getting an ident will confirm the ident.
If instead of an approach control radar malecontrol is talking about a display of radar information presented to TWR controllers (especially those who do not have radar ratings), I think the locally agreed/approved procedures and instructions would be the reference to be used.