Group of fliers intially start a journey (3,3)
I believe the answer is:
set off
'intially start a journey' is the definition.
I can't judge whether this definition defines the answer.
'group of fliers' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'fliers' becomes 'f' (this could be a standard abbreviation which I don't know about).
'set'+'of'+'f'='SET-OFF'
Can you help me to learn more?
(Other definitions for set off that I've seen before include "Counterbalance" , "Display - mount - start journey" , "Begin journey or detonate bomb" , "Commence journey or detonate" , "Leave - explode" .)