Originally Posted by
UserMark
I know changing carriers is supposed to be free, but is there ever any YQ extra charge? Suppose you buy a flight on one carrier (like AA) and then later decide you'd like to fly the same route on BA. Perhaps if you originally bought the flight with BA, the YQ might have been higher. If you change it to BA later, do they ever recalculate the YQ and ask you to pay more?
While you should not be charged the change fee, you are responsible for any difference in fees, taxes, and carrier surcharges caused by your change of carrier. So if switching to BA you should be prepared to pay the BA surcharges.
See, for example:
Flight code change