The new Los Angeles to Singapore route, eighteen hours, forty minutes, courtesy of Singapore airlines.
Next, not surprisingly, is Singapore to Los Angeles, although it is a full two hours, forty minutes shorter, because of air currents. Then comes New York to Hong Kong, sixteen hours.
Here is an article on how people stand it. Some sleep, some drink, and some argue politics with their seatmates. Airlines are now taking a hand in shaping on-board community. Virgin will be installing in-flight instant messaging on some of its longer flights, to encourage the formation of small discussion groups on the plane.
How about me?: I view any flight (that’s the flight, not the waiting) under six hours as a benefit, not a cost. It is a chance to do sustained reading and thinking without interruption. A ten hour flight remains tolerable if I have enough leg room. I need a stack of good books, some chocolate, and an assortment of cheeses. After ten hours my reading starts to veg out. But even then I would prefer in-flight institutions that tax people who try to communicate with me.
Addendum: Air genius Gary Leff informs me that a forthcoming NY-Singapore route, Singapore Air, will soon become the world’s longest direct flight.