I believe like most companies they only send back to those they are interested in. From what I know, when they recieve the application form back and they have reviewed it. You are either selected for interview or placed in their application pool. That is where mine is at the moment along with about 10,000 others (the figure they gave during the BALPA EOC conference in October).
You have to send an update whenever there is a significant change in hours, or at least every six months.
Hope that helps.
Moku.