Obsession of crew needing first class to return (5)
I believe the answer is:
mania
'obsession' is the definition.
(I've seen this before)
'crew needing first class to return' is the wordplay.
'crew' becomes 'man' (both can mean to staff or operate something).
'needing' means one lot of letters go next to another.
'first class' becomes 'ai' (A1 - top quality).
'to return' says the letters should be written in reverse.
'ai' in reverse letter order is 'ia'.
'man'+'ia'='MANIA'
'of' is the link.
(Other definitions for mania that I've seen before include "Aberration" , "Obsessional enthusiasm" , "Craze; overexcitement" , "Passion -- mood disorder" , "Over-enthusiasm" .)