Originally Posted by
findark
Yes, the mapping is well-defined on domestic routes, and this is it. The relevant characters from the current domestic format are in first and seventh position, eg WAA2KKFN. W has a secondary inventory of W (and books into Z), and F indicates it is a First fare.
But there's no way (just by looking at the fare code) to know that it books into Z, rather than J or C or P... that's what I was hoping for.