Fly the cockney across (5)
I believe the answer is:
hover
'fly' is the definition.
(hovering is a kind of flying)
'the cockney across' is the wordplay.
'the cockney' becomes 'h' (I can't explain this - if you can you should give a lot more credence to this answer).
'across' becomes 'over' (synonyms).
'h'+'over'='HOVER'
Can you help me to learn more?
(Other definitions for hover that I've seen before include "Remain in one place in the air" , "Hang in the air or waver" , "Float hanging in the air" , "Hang around (in air)" , "Low flying machine (10)" .)