MEWR course for crewman will soon been tri-service. Furthermore, it will no longer be 42 weeks but around 16 (i think). In theory an AAC crewman having been through this system should be able to jump straight from AAC to RAF. My personal opinion is that they should still do OASC selection the same as everyone else then straight to an OCU. We should open these guys with open to arms, after all, each fleet is cyring out for manpower.
Currently, since none of the AAC crewman (that i'm aware of) have been through the MEWR route OASC followed by MERW then OCF would be the best route.