Originally Posted by
canadiancow
Commuting mainline pilots, AFAIK, are not even entitled to J. Maybe a really old contract grandfathered some of them in?
Commuting pilots are just using their staff travel privileges, and can't bump anyone. They might be able to use some of their passes to confirm space in advance rather than be on standby, but they don't get to bump a paying customer from a seat, not in J, not in Y. Commuting staff (whether pilots or cabin crew) are those who choose to live somewhere other than their contractual base, and it's their responsibility to make their own way to their base for the start of a pairing. That can sometimes result in paying out of pocket for revenue tickets if SBY is looking dicey.
Deadheads are those making their way to and from assignments by the airline, where the airline elected to begin or end a pairing not at their home base. If a pilot was deadheading CUN-YVR, presumably he had operated a flight to CUN, but was not needed for a return.
In the case of the OP, I'm puzzled as to why this happened. CUN is not far enough away from any place whence AC flies to it that it needs a relief pilot, and even if the pilots have to overnight there rather than flying straight back, there shouldn't be any need for a deadhead, unless it were the last flight of the season or something like that.
Perhaps a case of a pilot becoming ill or otherwise unable to fly, having been replaced by someone who deadheaded down on a previous day, now deadheading home, or something along those lines. A situation like that would also explain why crew sched had not blocked off a seat farther in advance and allowed RM to fill the cabin.