Bypass road used by aircraft! (8)
I believe the answer is:
'aircraft' is the definition.
(I've seen this before)
'bypass road used by' is the wordplay.
'bypass' becomes 'skip' (I've seen this before).
'road' becomes 'lane' (a lane is a small road).
'used by' is a charade indicator (letters next to each other).
(Other definitions for skiplane that I've seen before include "Aircraft that can land on snow" , "Long accusatory speech" .)