Criticises airport site's setbacks (6)

I believe the answer is:

knocks

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This might be a double definition.

'criticises airport site's' is the first definition.
'knocks' can be an answer for 'criticises' (I've seen this before). I'm unsure of the 'airport site's' bit.

'setbacks' is the second definition.
(both can mean difficulties or unfortunate events)

Can you help me to learn more?

(Other definitions for knocks that I've seen before include "Bangs on door" , "Raps; criticises" , "Strikes with a sharp blow or finds fault with" , "Gentle taps" , "criticisms" .)

I've seen this clue in The Irish Times.

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