PhD
I'm doing my PPL now and I just came onto this airline forum out of general interest - I've got no interest in becoming a professional pilot. However I am an engineer and I do have a (research) masters degree.
I'd say, in general, PhDs are not a good idea. There are some specific circumstances where they are useful, like if you go into adademia or go into a research field in a large well funded corporation, but in general:
- They are a lot of work
- You do not get paid more at the end: infact you often get paid less
- You are seen as overqualifed or too bookish for most jobs
- You lose 3-4 years where you would otherwise be getting paid and getting more experienced in the general workforce
I'm 30-something and have a good career in engineering, still doing technical work. It pays well and it has taken me around the world. I can do a PPL without even thinking about the cost or having to save for it. I could even buy a not too used Mooney or something without breaking the bank. I don't have to work too hard (this is not in the UK obv, as engineering doesn't pay that well there). Most of my colleagues are in the same position as me, I'm not special or overly talented or anything.
I am 100% sure I would be getting paid less, have less freedom and be in a lower position now, if I had done a PhD instead of a masters.
If you do a PhD, think very carefully about what you are planning on doing for a career afterwards, esp as the flying may or may not work out. Consider if you really want to do a PhD or you would rather spend that time working in industry - neither option should make a difference to your flying one way or the other.