Good person on carriage is one in flight (5)
I believe the answer is:
stair
'is one in flight' is the definition.
(I've seen this before)
'good person on carriage' is the wordplay.
'good person' becomes 'st' (saint).
'on' is a charade indicator (letters next to each other).
'carriage' becomes 'air' (I've seen this before).
'st'+'air'='STAIR'
(Other definitions for stair that I've seen before include "section of flight" , "One step of a flight" , "One of a flight of steps" , "Step as part of flight" , "single step in a series" .)