Flying personnel/crew/staff used to have separate entries/exits to the airplanes on most of the European airports. The security people pretty much knew them and the reverse was true. Nobody could impersonate anybody. They could NOT. I do not know of any case. Contradict me if you can.
In US, where they did NOT have separate Entries/Exits for the flying crews (who are way and beyond. security checked prior to even being hired), nowadays, anybody with a GED can have a PILOT/AIRCRAFT CAPTAIN take his shoes off in front of the passengers.
Think US took major steps in preventing terrorism, by knocking the shoes/socks off of their own pilots?