Incapable airborne fighter left city in ruins (9)
I believe the answer is:
paralytic
'incapable' is the definition.
(thesaurus)
'airborne fighter left city in ruins' is the wordplay.
'airborne fighter' becomes 'para' (short for paratrooper).
'left' becomes 'L' (common abbreviation).
'in ruins' indicates anagramming the letters.
'city' is an anagram of 'ytic'.
'para'+'l'+'ytic'='PARALYTIC'
(Other definitions for paralytic that I've seen before include "Extremely drunk" , "Still" , "Drunk (informal)" .)