Crossword Genius

First class aviators in the services (4)

Ross

I believe the answer is:

aces

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'services' is the definition.
(ace is a type of serve in tennis)

'first class aviators' is the wordplay.
'first class' becomes 'ace'.
'aviators' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'ace'+'s'='ACES'

'in the' acts as a link.

Can you help me to learn more?

(Other definitions for aces that I've seen before include "excellent service" , "Two will make deuce" , "Champions" , "wartime pilots?" , "Experts (in their field)" .)

I've seen this clue in the Evening Standard.
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