A service that's revolutionary at a distance (4)
I believe the answer is:
afar
'at a distance' is the definition.
(I've seen this before)
'a service that's revolutionary' is the wordplay.
'service' becomes 'RAF' (Royal Air Force).
'that's revolutionary' is a reversal indicator (letters revolve around).
'raf' in reverse letter order is 'far'.
'a'+'far'='AFAR'
(Other definitions for afar that I've seen before include "long way back" , "quite some distance" , "A long way away" , "Way-out" , "Distant parts" .)