Lark, notice, in flight (8)
I believe the answer is:
escapade
'lark' is the definition.
(I know that lark can be written as escapade)
'notice in flight' is the wordplay.
'notice' becomes 'ad' (short for advert).
'in' means one lot of letters goes inside another.
'flight' becomes 'escape' (flight can mean an escape).
'ad' going within 'escape' is 'ESCAPADE'.
(Other definitions for escapade that I've seen before include "Madcap adventure" , "Wild adventure" , "Daring adventure" , "Caper" , "Antic" .)