Returning, Air Force area is a long way off (4)
I believe the answer is:
afar
'long way off' is the definition.
(I've seen this in another clue)
'returning air force area' is the wordplay.
'returning' shows that the letters should be reversed in order.
'air force' becomes 'RAF' (Royal Air Force).
'area' becomes 'a' (maths abbreviation).
'raf'+'a'='rafa'
'rafa' in reverse letter order is 'AFAR'.
'is a' is the link.
(Other definitions for afar that I've seen before include "Way-out" , "quite some distance" , "(From/at) a great distance" , "Pull out at a distance" , "Many miles away" .)