What do airlines do when their annual fuel bills double? For one thing, they put their planes on a diet.

With fuel now an airline's single largest expense

(followed by labor), CNN reports that carriers are desperately trying anything that will save money at the pump. Reducing aircraft weight is one strategy, so the airlines are going over their planes with a fine tooth comb and tossing anything that isn't absolutely necessary .

You have to give it to the airlines, they've left no stone unturned. Just how far are they going?

US Airways is chucking meal carts and replacing them with models that are 12 pounds lighter. They've also tossed the glassware in first class in favor of less jet-set but lighter plastic cups. Carriers also are pulling magazine racks, trash compactors and ovens

(because honestly, what U.S. airline is broiling up hot meals these days?)

American Airlines has all but called in Jenny Craig to shave weight from its fleet, pulling in-seat phones and their heavy wiring, removing lavatory power converters and investing in lighter silverware for business class passengers. American, which has something of a reputation for chopping costs (its legendary former CEO Bob Crandall once bragged that he saved the airline $40,000 by removing olives from first class dinner salads), has fired up the troops by forming an employee-driven "Fuel Smart Team" charged with continually searching for ways to save energy. Though it should be noted that American was lambasted earlier this year for flying a 225-seat Boeing 777 from Chicago to London with just five passengers on board.

Does lightening a plane's load really make much of a difference? The airlines think so.

JetBlue says removing extra trash bins and other supplies will shave $16,000 off their daily fuel expenditure from each three hour flight. US Airways says using lighter beverage carts will save $1.7 million in annual fuel costs.

American expects to cut fuel consumption by 111 million gallons through its weight reduction efforts, and the airline's Ned Raynolds says that the Fuel Smart program is saving the airline $200 million a year.

But airlines are balancing the urge to slim down with the need to maintain appearances, especially in first and business class. Facing competition on long-haul routes from far sexier international airlines (ever seen the first class cabin on one of Emirates' planes?) the major US airlines have been making big investments in premium class seating, dining and service.

When it comes to wooing the big-money passengers, plastic cups probably aren't going to cut it, no matter how much fuel they save.

Sources: CNN, Business Week.

Photo by Associated Press.