One who flies through the air antenna first (9)
I believe the answer is:
aerialist
'one who flies through the air' is the definition.
(circus performer)
'antenna first' is the wordplay.
'antenna' becomes 'aerial' (synonyms).
'first' becomes 'ist' (ist resembles 1st).
'aerial'+'ist'='AERIALIST'
(Other definitions for aerialist that I've seen before include "Highly-regarded performer" , "Trapeze acrobat" , "trapeze artist" , "skier" .)