One-off programme for aviator (5)
I believe the answer is:
pilot
This clue is a double definition.
'one-off programme' is the first definition.
(I've seen this before)
'for aviator' is the second definition.
(pilot is a kind of aviator)
(Other definitions for pilot that I've seen before include "Guide, flyer" , "Steer (a ship or plane)" , "Captain of plane or boat" , "Guide, steer" , "Test or trial (project or programme)" .)