From memory, it's a situation full of 'grey areas' - in other words, it depends on you, and how much each side want/need you to make the move.
I did it from the RAF to FAA rather than the Army and already had all the quals the RN wanted - hence it was easy to get in, and half a day at BRNC was all that was required before I had some nice new gold stripes. The bigger issue was actually getting the RAF to let me go - in the end I had to PVR and do the full time. So I took full resettlement (which was a nice 3 month break on full pay) before starting with the FAA.
My top tip is to make sure your 'sponsor' at the RN end is proactive with your Army career people - you don't want to get caught between the gaps. Pension transfer is another thing - but that has not turned out to be an issue (but I was on 75 so definitely get that checked out).
And good luck! The FAA is a world of its own - for good and for bad!