Ace within radio frequency for all his mates? (3) --F. I'm thinking RF for radio frequency with A for ace in the middle - RAF, but not seeing any logic there.
The RAF one.
When a clue has a question mark at the end it often means the the answer somehow wraps up the whole clue.
I interpret this poor clue to mean a flying ace and his mates are in the RAF and they are in contact with each other by radio. Unless someone thinks otherwise.