Returning in local air transport is a test (5)
I believe the answer is:
trial
'test' is the definition.
('trial' can be a synonym of 'test')
'returning in local air transport' is the wordplay.
'returning' is a reversal indicator.
'in' indicates a hidden word.
'lairt' is hidden in the letters of 'local air transport'.
'lairt' reversed gives 'TRIAL'.
'is a' acts as a link.
(Other definitions for trial that I've seen before include "Criminal court case" , "Annoyance" , "Judicial examination" , "Troublesome thing; test" , "show at Crufts?" .)