Is engaged in air support, backing identification (9)
I believe the answer is:
diagnosis
'identification' is the definition.
(diagnosis is a kind of identification)
'is engaged in air support backing' is the wordplay.
I cannot really understand how this works, but
'is' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for diagnosis that I've seen before include "Doctor's verdict" , "Identification of an illness" , "Identification of disease" , "medical opinion" , "doctor's opinion" .)