One group of fliers when turning up for hunting expedition (6)
I believe the answer is:
safari
'hunting expedition' is the definition.
(synonyms)
'one group of fliers when turning up' is the wordplay.
'one' becomes 'i' (Roman numeral).
'group of fliers' becomes 'RAF' (Royal Air Force).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'turning up' says the letters should be written in reverse.
'i'+'raf'+'as'='irafas'
'irafas' written backwards gives 'SAFARI'.
'for' acts as a link.
(Other definitions for safari that I've seen before include "Hunting journey" , "tropical trip" , "As fair as an African expedition" , "African hunting expeiditon" , "Hunting trip" .)