The migration itself may be valuable, if treated properly. Many airlines have had very public issues when their mainframe had problems running (often power issues, but sometimes other things); a migration to x86 includes accepting and handling more failures, which may include having a warm second site available.

You can certainly have a warm second mainframe too, and I think most large banks are run that way, but it wouldn't be very fashionable to add that to your airline now, if it wasn't already there.