Working fairs endlessly broadcasting (2,3)
I believe the answer is:
on air
'broadcasting' is the definition.
(I've seen this before)
'working fairs endlessly' is the wordplay.
'working' becomes 'on'.
'endlessly' indicates the central letters (the ends of the words are removed).
The centre of 'fairs' is 'air'.
'on'+'air'='ON AIR'
(Other definitions for on air that I've seen before include "Broadcasting live" , "put out" , "Cushioned" , "If you're really happy, you'll float here" , "now showing" .)