The air crew produces witness caught by shed (3,6)
I believe the answer is:
sea shanty
'the air crew produces' is the definition.
(song or air which a ship's crew might produce)
'witness caught by shed' is the wordplay.
'witness' becomes 'see' (synonyms).
'caught' indicates a 'sounds like' (homophone) clue (to catch something can mean to hear it).
'by' is a charade indicator (letters next to each other).
'shed' becomes 'shanty' (I've seen this before).
'see' is a homophone of 'sea'.
'sea'+'shanty'='SEA SHANTY'
(Other definitions for sea shanty that I've seen before include "Traditional song sung by sailors" , "A certain air" .)