Qualification of an aviator or of his side joint (10)

I believe the answer is:

airmanship

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'qualification of an aviator or of his' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'side joint' is the wordplay.
'side' becomes 'airman' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'joint' becomes 'ship' (I've seen this in other clues).
'airman'+'ship'='AIRMANSHIP'

Can you help me to learn more?

(Another definition for airmanship that I've seen is " Need for pilot".)

I've seen this clue in the Sydney Morning Herald.

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