Hyperbaric Departure Lounge

Aircraft fly by having at least as much lift as weight. Lift is provided by aerofoils and airspeed, airspeed is provided by thrust, which costs fuel and therefore money. In recent years, United Airlines, among others, have begun replacing the pilots flight bags with iPads and the like. The flight bag would normally be filled with >20kg of flight plans, navigational charts weather reports and other assorted paperwork. This weight saving translates to a big fuel saving when applied to a large airline <link>.

Now, when SCUBA diving, many people pee. More than usual. The phenomenon, termed "immersion diuresis" has two components, cold, and pressure. Cold constricts the vast network of capillaries in the skin, increasing blood pressure slightly, and pressure increases... well, pressure generally. Both of these combine to force more water through the kidneys by increasing filtration rate. Meaning you pee more.

Now, if airlines were to collude with airports on this, then the departure lounge should be deliberately chilly, and hyperbaric. Squeezing an extra 100l pee out of 200 passengers is a lot better than swapping that ipad in. The good thing about loosing weight off the aircraft is you don't need as much fuel. Which means the aircraft needs less fuel to carry THAT fuel, and so on.

So, departure lounges, high pressure, cold, toilets like palaces. For extra points, get the passengers to burn off glycogen and its associated water by making sure the snacks are super expensive... oh, they're onto that one.