Depends how old you are joining. You might get 2 tours initially and then a further tour as a squadron commander after 4 or 5 years on the ground.
You might be able to transfer elsewhere, but you probably won't want to relinquish your flying pay. You could then transfer to the RAF or RN (if it still exists).
Or you could go to the RAF or RN to start with and try and wangle an exchange tour.
The bottom line is - if you want to fly permanently in the Army, don't join as an officer. We are the only service that has non-commisioned aircrew. I've done a 5 year stint on the ground and I didn't like it at the time, but even I have to admit that it makes me a lot more employable outside the army in addition to my commercial licence (which you don't get gratis either, just in case you were wondering!)
But all that said - you won't regret it if you join the AAC - any part of the military that has 1.5% of the personnel and 30% of the budget can't be no fun can it?
mind you, it is 30% of not a lot come to think of it!