Replacement vessel gets you to US airport (6)
I believe the answer is:
newark
'to us airport' is the definition.
(I've seen this before)
'replacement vessel' is the wordplay.
'replacement' becomes 'new'.
'vessel' becomes 'ark' (ark is a kind of vessel).
'new'+'ark'='NEWARK'
'gets you' acts as a link.
(Other definitions for newark that I've seen before include "Market town on river Trent" , "US port" , "Town on river Trent where King John died" , "east coast port" , "Notts. town; NJ city" .)