The most common and most likely answer to this crossword clue is the 2 plus 3 letter word ON AIR
I've seen this crossword clue in Financial Times
O
N
A
I
R
More clues leading to the result ON AIR
- Radio show could be playing song
- Love new song being broadcast
- Revolutionary extract from Wagnerian opera being broadcast
- Playing song live
- Suave young socialite is lost, broadcasting
- Radio show might be playing song
- Addicted to tune being broadcast
- Broadcasting in Hungarian, obviously uplifting
- Broadcasting revolutionary elements of vegetarian option
- One may happily walk here during broadcast
Buddy explains!

The straight part
We know that "Broadcasting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case broadcasting = on air.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ON AIR mean?
ON AIR adjective- Broadcast (as opposed to recorded).
- Actually broadcasting on a radio or television station (as opposed to just recording for later transmission).