He gains a cast at this airport! (8)
I believe the answer is:
heathrow
'this airport' is the definition.
(London airport)
'he gains a cast' is the wordplay.
'gains' means one lot of letters go next to another.
'cast' becomes 'throw' (synonyms).
'he'+'a'+'throw'='HEATHROW'
'at' is the link.
(Other definitions for heathrow that I've seen before include "our counterpart of Charles de Gaulle" , "London airport" , "London's busiest airport" , "London's main airport" , "site for airport" .)