There is a steep approach button which allows the aircrafts spoilers to be extended as it goes down the 5.5 degree glide path (contrary to a standard 3 degree ILS approach). I'm sure it also changes a few other systems as well but I can't recall them off the top of my head.
The A318 crews are LHR-based A320-fleet type rated with some training to handle the steep approach at LCY as well as Atlantic Ops and American differences which the general A320 fleet will not experience on a regular basis in scheduled operations.
The A318 operation is very senior however so only the most senior crews get to join the A318 'club'.