There doesn't appear to be much gen on the AAC on this forum; so as I considered the AAC to at one time I'll explain as much as I can as it's fairly different to the RAF/RN process.
Firstly, I assume that you are considereing applying to the Army as an officer with a view to entering RMAS? If you're not familiar with the process of applying for an Army commission then you should examine it in detail. On passing the RCB and being offered a place at RMAS you do so with no guarantee of the regiment that you will be commissioned into. At an early stage during RMAS you apply to 3-4 regiments. At various points regimental interviews take place and you are advised of the regiment that you will join by about week 30. AAC is by far one of the most popular choices.
If you express an interest in the AAC prior to attending the RCB then you go to Middle Wallop for a look and an interview on successful passing of the aptitude tests at RAF Cranwell. If successful at this stage then you'll be sponsored by the AAC and will be able to attend Flying Grading prior to starting RMAS on passing the RCB. If you pass grading then you stand a reasonable chance of joining the regiment, although you must sit an arduous regimental interview board and do well at Sandhurst.
As the AAC is very much after good officers that can fly, and not vice versa, they are slightly more lenient on medical standards apparantly. BUT, if you visit midlle wallop you'll find all AAC officers are very "Army"!
If you're sole wish is to fly then this is the least adviseable route to follow as there are no guarantees until the end of Sandhurst.