Driver having to edge skyward (5)
I believe the answer is:
Here is my best explanation:
'driver' is the definition.
(I have seen 'Driver of aircraft' mean 'pilot' so perhaps 'driver' could also mean 'pilot')
'to edge skyward' is the subsidiary indication.
'edge' becomes 'lip' (lip is a kind of edge).
'skyward' says the letters should be written backwards (in a down clue, letters go up).
'tolip' in reverse letter order is 'pilot'.
'having' is the link.
(Other definitions for pilot that I've seen before include "Plane driver", "Flier - guide", "Experimental programme", "Small flame that ignites a gas boiler", "air traffic controller?", "Airman", "Driver of aircraft", "may be up in the clouds", "Plane flier" and "aviator".)