Originally Posted by robb
I've wished for the same thing about the XP, XI, but I simply figure that if there are three classes and there's a West-coast city as the origin or destination, it's XP; if there are three classes and there's an East-coast city, then it's XC/XI.
That's held true for me so far, but then again, I haven't flown a lot of LAX-IAD

Flights to Europe from The West Coast are normally XC/XI and to Asia XP.