Airline with 100 staff (5)
I believe the answer is:
baton
'staff' is the definition.
(I've seen this before)
'airline with 100' is the wordplay.
'airline' becomes 'BA' (British Airways).
'with' is a charade indicator (letters next to each other).
'100' becomes 'ton' (ton can informally mean a hundred).
'ba'+'ton'='BATON'
(Other definitions for baton that I've seen before include "Conductor wields it - or a policeman" , "It's passed in a relay race" , "weapon" , "Staff" , "A stick for a conductor and policeman" .)