Ceremony welcoming pilot officer’s return (7)
I believe the answer is:
riposte
'return' is the definition.
(synonyms)
'ceremony welcoming pilot officer's' is the wordplay.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'pilot officer's' becomes 'pos' (short for pilot officer).
'rite' enclosing 'pos' is 'RIPOSTE'.
(Other definitions for riposte that I've seen before include "Rejoinder" , "Return thrust or repartee" , "Reply, response" , "Rejoin" , "Counter-thrust" .)