Engineers coming in to help broadcast (5)
I believe the answer is:
aired
'broadcast' is the definition.
(synonyms)
'engineers coming in to help' is the wordplay.
'engineers' becomes 're' (abbreviation for Royal Engineers).
'coming in to' means one lot of letters goes inside another.
'help' becomes 'aid' (synonyms).
're' placed into 'aid' is 'AIRED'.
(Other definitions for aired that I've seen before include "Ventilated, or hung out to dry" , "Ventilated in the outdoors?" , "Exposed for drying" , "Expressed publicly" , "Exposed to breeze for freshening - say damp clothes" .)