Fighter pilot carrying 1000kg right now (2,4)
I believe the answer is:
at once
'right now' is the definition.
(I've seen this before)
'fighter pilot carrying 1000kg' is the wordplay.
'fighter pilot' becomes 'ace' (an ace pilot).
'carrying' means one lot of letters goes inside another.
't000kg' becomes 'ton' (I am not sure about this - if you are sure you should believe this answer much more).
'ace' going around 'ton' is 'AT ONCE'.
Can you help me to learn more?
(Other definitions for at once that I've seen before include "Immediately, without delay" , "'Without delay (2,4)'" , "Immediately, this instant" , "This minute!" , "This instant, hop to it" .)