Jet surpasses birds (9)
I believe the answer is:
blackcaps
'birds' is the definition.
(blackcap is a kind of bird)
'jet surpasses' is the wordplay.
'jet' becomes 'black' (similar in meaning).
'surpasses' becomes 'caps' (I can't justify this - if you can you should give a lot more credence to this answer).
'black'+'caps'='BLACKCAPS'
Can you help me to learn more?
(Other definitions for blackcaps that I've seen before include "they have beaks" , "Judges used to have them" .)