When I left C5 last year, you could "opt-in" to Aviate, in which case you had to wait your turn but might flow eventually. But if you didn't opt in you could apply off the street, however I never heard of anyone being hired that way, and the conventional wisdom was that your chances of being hired off the street were practically nil since United of course wouldn't want to poach their own regional feed. There were several different versions of the Aviate program, or CPP as it was called before that, while I was at C5 so for all I know the rules may have changed again. Before 2022 it wasn't a true flow but an opportunity to interview.