Set out about eleven for departures (5)
I believe the answer is:
exits
'for departures' is the definition.
('exit' can be a synonym of 'departure')
'set out about eleven' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'about' indicates putting letters inside.
'eleven' becomes 'xi' (Roman numerals).
'set' with letters rearranged gives 'ets'.
'ets' going around 'xi' is 'EXITS'.
(Other definitions for exits that I've seen before include "Egresses" , "Ways out" , "Departs" , "Leaves the stage" , "Withdraws" .)