TL
Its not something we do very often at all. I rang Cranfield because we could seee on radar there were a few of you about. The only reason we did on this particular occasion was because we would have apprecaited a call there & then for the benefit of one of our trainee assistants. They have to be compotent at being able to handle a freq & know what they are doing up to a point so that if the controller (during the quiet hours when there is only one controller on), nips to the loo they are able to handle the call for the v short period he is out the ops room.
Regards
DD