Legislator flying Martian airplane (15)
I believe the answer is:
parliamentarian
'legislator' is the definition.
(I've seen this before)
'flying martian airplane' is the wordplay.
'flying' indicates an anagram (letters fly around into new positions).
'martian'+'airplane'='martianairplane'
'martianairplane' anagrammed gives 'PARLIAMENTARIAN'.
(Other definitions for parliamentarian that I've seen before include "Eg, an MP" , "politician" , "legislator" , "elected representative?" .)