Crossword Genius

The gang are of service when on air (4)

Ross

I believe the answer is:

crew

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'the gang' is the definition.
(synonyms)

I don't understand the remainder of the clue.

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(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" .)

I've seen this clue in the Evening Standard.
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