Airline travel is almost 100 years old, yet it remains an enigma to most of us everyday travelers. After all, each time we take a flight, there are complicated code words, airport acronyms, and an intricate ballet of take-offs and landings and loading and unloading. And there are other mysteries, too, that pop up in flight, such as: What do airlines do with all those back issues of SkyMall? Sometimes these mysteries should probably stay mysterious — after all, do we really want to know what happens when we flush an airplane toilet?