Longman Dictionary of Contemporary English
Wiktionary
a. broadcast (as opposed to recorded). adv. Actually broadcasting on a radio or television station (as opposed to just recording for later transmission).
Usage examples of "on-air".
At a nod from Minh, he began, having allowed for an introduction to be written later, which would precede the on-air showing.
After all that I'm still a line producer, no on-air anything, doing the same job they're giving to twenty-two-year-old bimbos fresh out of school.
The story was shaped by the producer, and narrated by the on-air star, who flew in for a single day, did the stand-ups and the major interviews, and then flew on to the next shoot, leaving the producer to cut the tape.
The success of that first on-air visit led to regular appearances on the program, and when Marge moved on to host a television program, Susan was invited to replace her on the daily radio talk show.