Ronnie3585, hi. I'm an aviation lawyer in the City (although one on the verge of canning it and going off to fly, which probably isn't the most sensible thing to do reading some of the other threads on here).
I pretty much engineered it that I got into this field: I had done UAS, PPL etc. but when I graduated in the mid-90s flying jobs were in short supply.
You need to think what you mean by "aviation lawyer". There are three main fields really: finance, regulatory and litigation. I specialize in the first two. No additional qualification is strictly necessary for the finance work: it's really banking with an aeroplane twist. That said, enthusiasm for the area undoubtedly makes it more enjoyable - the hours can pretty horrendous when you're on international deals. The major upside is that most other aircraft finance lawyers you come across are generally good guys - it's a small community so you have to get on. There are other definite upsides like lots of involvement with manufacturers and airlines, with trips around the world to "deliver" aircraft. You'll also be making enough to carry on flying privately, if that's your thing.
Regulatory work is different. An even smaller pool of firms to choos from and I would definitely recommend looking at a Masters in aviation law: it gives you a real boost in knowledge and demonstrates your commitment. I did the course at UCL - absolutely excellent although places like McGill offer even more aviation-intensive Masters courses. But, for me, this is the really interesting work. Acting for airlines, airports, government bodies on everything from setting up an airline, route rights (not so much of that any more), airspace issues. The work ranges from the hugely practical - getting permission for wet leases overnight for an airline with an AOG - to the theoretical (such as advising on airspace issues).
Litigation (pretty much liability work): additional qualifications again not strictly necessary. Just make sure you pick one of the good aviation litigation firms.
That last point worth bearing in mind for all areas: make sure you get into one of the recognised top firms.
Good luck!