First person in the scheme is an airman (5)
I believe the answer is:
pilot
'an airman' is the definition.
(I know that pilot is a type of airman)
'first person in the scheme' is the wordplay.
'first person' becomes 'I' (first-person pronoun).
'in the' means one lot of letters goes inside another.
'scheme' becomes 'plot' (plot is a kind of scheme).
'i' put inside 'plot' is 'PILOT'.
'is' acts as a link.
(Other definitions for pilot that I've seen before include "Steer (a ship or plane)" , "Aviator" , "experimental programme" , "Test or trial (project or programme)" , "Navigator" .)