Pilot backing international air traffic control (5)
I believe the answer is:
trial
'pilot' is the definition.
(synonyms)
'backing international air traffic control' is the wordplay.
'backing' shows that the letters should be reversed in order.
'control' says the answer is hidden in the clue (I've seen 'controlling' mean this (the solution is controlled or contained)).
'lairt' can be found hidden inside 'international air traffic'.
'lairt' backwards is 'TRIAL'.
(Other definitions for trial that I've seen before include "Court proceedings" , "Pilot" , "Court appearance on charge - it's an ordeal" , "Court hearing" , "Judicial hearing and judgment" .)