Originally Posted by
SLC777RES
M is not completely meaningless.
As many FT'ers will attest, M is significant, particularly in an Irop when you're flight cancels and the next flight is an RJ or sold out in F and DL rebooks you in Y and claims it owes you zero compensation for the down-grade. This happens at all the legacies that offer these UP type fares.
But how is that any different than a BUP or KUP fare? It's the "UP" part that allows the above to happen, not the first character of the fare basis code.