Thank you for your informative answers!
After your comments on the subject of my PhD and gaining some actual work experience, I'm indeed starting to rethink if getting a PhD is really the best option for me.
There is barely any aerospace research done at universities here in Belgium. So having a topic that is closely related to flight test would be difficult. Of course if I really wanted to I could go to Delft for my PhD.
I'll probably try and do a PhD very closely related to flight testing. If I can't find this kind of doctoral position I'll gain some work experience instead.
Genghis, thank you very much for all your suggestions! I think I know were to invest my time and energy to further my goal of becoming a FTE. The master at Cranfield seems to be very interesting.
I'll also try to get more flying hours and try to become part of the flight test community.
I have one more question. Is there a lot of flight testing going on in the military (more specifically the Belgian air force)?
I know the technical staff consists largely of civilians. And it's one of the biggest employers for aerospace engineers (there are very few) in Belgium.