Check first few are not too heavy for airborne experiment (4,6)
I believe the answer is:
test flight
'airborne experiment' is the definition.
I know nothing about this answer so I can't tell whether this works.
'check first few are not too heavy' is the wordplay.
'check' becomes 'test' (as in testing or checking something works).
'first few' becomes 'f' (lst letter of 'few').
'are not too heavy' becomes 'light' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'test'+'f'+'light'='TEST FLIGHT'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for test flight that I've seen before include "First trip up" , "Trial of new aeroplane" , "requires an experienced pilot" , "Trial of new aircraft" , "Trial of a new plane" .)