In flight notice lark (8)
I believe the answer is:
escapade
'lark' is the definition.
(both can mean an adventure or amusement)
'in flight notice' is the wordplay.
'in' is an insertion indicator.
'flight' becomes 'escape' (flight can mean an escape).
'notice' becomes 'ad' (short for advert).
'escape' placed around 'ad' is 'ESCAPADE'.
(Other definitions for escapade that I've seen before include "Madcap adventure" , "Risky adventure" , "Jolly jape" , "Adventurous T [TREAT]" , "Piece of reckless mischief" .)