As @Intruder said, don't get into anything too aviation-specific.
In my case, Ergonomics/Human Factors was (I hope) a good choice:
1) Covers aviation
2) Covers many non-aviation (safety-critical) industries
3) Applies in a general sense to normal operations in other industries
4) The Aviation industry lead the way with CRM/HF
5) Your command skills become transferable to other industries, as a facilitator, and...
6) The subject covers all the 'good bits' of psychology (without cutting up dead rats - unless that’s your thing?)
Not suggesting that you follow this, but if whatever you study can tick some/most of these, especially the 'fun' part then I would definitely recommend this.
I would also add that there are probably too many pilots with MBAs, or Aviation Management Masters, that aren't going anywhere. Easy sell for the institutions to rake in outrageous fees, for a product that doesn’t suit.