Trying to get away by air (2,6)
I believe the answer is:
in flight
This clue is a double definition.
'trying to get away' is the first definition.
(I've seen this before)
'by air' is the second definition.
(I've seen this before)
(Other definitions for in flight that I've seen before include "Sort of meal" , "escapee?" , "Running" , "Sort of meals, say, for eating up" , "Trying to get away" .)