American and Delta have called it quits – Photo: John Nguyen | AirlineReporter

Some parts of the airline industry are very “cloak-and-dagger,” but once in a while something rears its ugly head and seems like it could be a bad thing, if only you knew what the heck was going on.  Such is the case now, as two of the largest airlines in the world, who also happen to be bitter rivals, American Airlines and Delta Air Lines, abruptly ended their interline agreement on September 15.

Why would direct competitors have such a partnership in place, and what does it mean for the flying public?