Regular air service (8)
I believe the answer is:
evensong
'service' is the definition.
(type of church service)
'regular air' is the wordplay.
'regular' becomes 'even' (similar in meaning).
'air' becomes 'song' (air can mean a piece of music).
'even'+'song'='EVENSONG'
(Other definitions for evensong that I've seen before include "... Prayers" , "Religious service" , "Late afternoon church service" , "6 [SERVICE] ?" , "Anglican service" .)