Agreement may be dispatched after airports vacated (6)
I believe the answer is:
assent
'agreement' is the definition.
(assent is a kind of agreement)
'dispatched after airports vacated' is the wordplay.
'dispatched' becomes 'sent' (I've seen this before).
'after' means one lot of letters go next to another.
'vacated' says to hollow out the word (remove centre letters).
'airports' with its centre removed is 'as'.
'sent' after 'as' is 'ASSENT'.
'may be' acts as a link.
(Other definitions for assent that I've seen before include "Permission" , "Consent or approval" , "Agree, acquiesce" , "Accede, agree" , "Give the thumbs-up" .)