Unconventional air missing A flat (9)

I believe the answer is:

irregular

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'unconventional' is the definition.
(similar in meaning)

'air missing a flat' is the wordplay.
'missing' suggests deleting specific letters.
'flat' becomes 'regular' (I can't explain this - if you can you should give a lot more credence to this answer).
'air' with 'a' removed is 'ir'.
'ir'+'regular'='IRREGULAR'

Can you help me to learn more?

(Other definitions for irregular that I've seen before include "Disorderly, uneven" , "Uneven - inappropriate" , "Against the rules" , "Unpredictable" , "Unconventional" .)

I've seen this clue in The Irish Times.

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