It's used in flight (by the RAF out East?) (7)
I believe the answer is:
feather
'it's' is the definition.
I can't judge whether this definition defines the answer.
'in flight by the raf out east?' is the wordplay.
'in flight' indicates anagramming the letters (the letters fly around).
'by' is a charade indicator (letters next to each other).
'out' indicates putting letters inside.
'east?' becomes 'E' (abbreviation).
'the' after 'raf' is 'rafthe'.
'rafthe' with letters rearranged gives 'feathr'.
'feathr' placed around 'e' is 'FEATHER'.
'used' is the link.
Can you help me to learn more?
(Other definitions for feather that I've seen before include "One of a bird's waterproof covering" , "A white one denotes cowardice" , "Part of a bird's plumage" , "The fear (anag) - type of bed" , "Prov. light part of bird" .)