Iver
I'm not sure of what happens exactly. I joined on the fleet I wish to be on. 12-18 months ago we were all given the choice to bid for our desired fleet and seat. Nothing similar has happened since. I gather that the fleet transferees usually get some sort of Boeing or Airbus choice. Recent refugees from the A300 fleet had a choice of anything. The setup is that initially you are meant to join onto the 320 and then transfer either big Airbus or Boeing. That then supposedly governs your progression afterwards. Some still join directly onto the 330 or 777.
The basic facts are that a lot of wide body aircraft are on order which means that if you get put on the 320 initially you can expect a move if you want within a reasonable timescale. If you stay in Airbus world within the airline you may end up back on the 320 for your upgrade.
Spanner