The gang are of service when on air (4)
I believe the answer is:
crew
'the gang' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for crew that I've seen before include "Gave wake-up call" , "Train team" , "Ship/plane operators" , "Sailors -- boasted" , "Very short haircut for the ship's complement" .)