One flying out of Yugoslavia to Romania (7)
I believe the answer is:
aviator
'one flying' is the definition.
(I've seen this before)
'out of yugoslavia to romania' is the wordplay.
'out of' says the answer is hidden in the clue.
'AVIATOR' can be found hidden inside 'yugoslavia to romania'.
(Other definitions for aviator that I've seen before include "one in a crate?" , "Aircraft pilot" , "Aeronaut" , "Flyer, pilot" , "Air pilot" .)