Ace pilots rising a long way off (4)
I believe the answer is:
afar
'a long way off' is the definition.
(I've seen this before)
'ace pilots rising' is the wordplay.
'ace' becomes 'a' (abbreviation).
'pilots' becomes 'RAF' (Royal Air Force).
'rising' says the letters should be written in reverse (in a down clue, letters go up).
'raf' reversed gives 'far'.
'a'+'far'='AFAR'
(Other definitions for afar that I've seen before include "Remote" , "from baseline to baseline?" , "Way-out" , "Distant, not near" , "quite some distance" .)