Planned trip with publicity ace some time before autumn (8)
I believe the answer is:
pratfall
'planned trip' is the definition.
'publicity ace some time before autumn' is the wordplay.
'publicity' becomes 'pr'.
'ace' becomes 'a'.
'some time' becomes 't'.
'before' says to put letters next to each other.
'autumn' becomes 'fall' ('fall' can be a synonym of 'autumn').
'pr'+'a'+'t'+'fall'='PRATFALL'
'with' acts as a link.
(Other definitions for pratfall that I've seen before include "Embarrassing mistake" , "Slip" , "humiliating blunder" , "embarrassment" , "Humiliating failure (US slang)" .)