Former partner raised fare to go on American flight (6)
I believe the answer is:
exodus
'flight' is the definition.
(exodus is a kind of flight)
'former partner raised fare to go on american' is the wordplay.
'former partner' becomes 'ex'.
'raised' says the letters should be written in reverse.
'fare' becomes 'do' ('do' can be a synonym of 'fare').
'to go on' says to put letters next to each other (in a down clue, some letters go on top of others).
'american' becomes 'us'.
'do' reversed gives 'od'.
'ex'+'od'+'us'='EXODUS'
(Other definitions for exodus that I've seen before include "Flight of the Israelites out of Egypt, led by Moses" , "Mass departure of people as of Jews from Egypt" , "Departure of the Israelites from Egypt, led by Moses" , "A mass departure of people, as in Bible" , "Second book of the Bible" .)