Choose part of helicopter (3)
I believe the answer is:
opt
'choose' is the definition.
(both can mean to pick something)
'part of helicopter' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'OPT' is hidden within 'helicopter'.
(Other definitions for opt that I've seen before include "Decide between possibilities, choose" , "Pick from pot" , "Have preference for something" , "Plump for" , "Elect" .)