Very Sneaky -As far as I'm aware you can't be streamed to the pilot role without attending flight screening, so I would assume that this would take place at some point during RMC. As preo mentioned earlier, there may be an opportunity to do so within the first 12 months. If selected for the aviation stream, all GSO candidates go through BFTS at the conclusion of RMC.
I may have some (dated) information to add to this. Prior to the advent of SSOs all Army pilots were required to complete the full course at RMC, or the last year if they attended ADFA.
During the first year we were dragged into a large lecture theatre and 'tested for aptitude'. Aviation and languages are the two I remember specifically. Those that tested as 'gifted' were streamed into Aviation or Intelligence Corps after graduation.