Airport approximation
I believe the answer is:
eta
'airport approximation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eta that I've seen before include "giving expected termination of journey" , "Seventh Greek letter" , "Member of Greek set a" , "Greek letter E; estimated time of arrival (abbr.)" , "when you can hope to receive it" .)