Where pilots will fly is not yet decided (2,2,3,3)
I believe the answer is:
up in the air
'not yet decided' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for up in the air that I've seen before include "Where skiers go" , "skylarks singing here?" , "open to debate" , "Where skier may be seen" , "Not sure" .)