Field in biplane race heading westward (5)
I believe the answer is:
arena
'field' is the definition.
(I know that arena is a type of field)
'in biplane race heading westward' is the wordplay.
'in' says the answer is hidden in the clue.
'heading westward' says the letters should be written backwards.
'anera' is hidden in the letters of 'biplane race'.
'anera' reversed gives 'ARENA'.
(Other definitions for arena that I've seen before include "Field of combat" , "Sphere of intense activity" , "bowl? Possibly" , "Playing field or boxing ring" , "Place of great activity" .)