SEATTLE -- A fuel cell is pretty simple in concept: feed in two gases, oxygen and hydrogen, and a catalyst that helps combine those two common elements into water. When the elements combine, electricity is created, along with heat.

Fuel cells have been used to help power space craft, and they are in growing in use in countries like Japan to power buses and, soon, cars.

But could fuel cells power airplanes? Could they cut the use of expensive jet fuel and, indirectly, make flying a little greener?

The electricity that runs everything from the electronic displays in the cockpit to the reading light above a passenger's seat are powered by jet fuel. A commercial airliner's engines drive generators to power the plane's electronics.

But decades down the road, fuel-cell technology could provide much of that electric power and even replace some of the jet fuel dedicated to moving the plane through the air.

An experiment into the practicality of this concept is now underway at Boeing Field. Boeing is testing a new American Airlines 737-800 that's equipped with a giant fuel cell takes takes up most of the aft baggage well.

The plane is called the Eco-Demonstrator, and so far it s been used to test ways to reduce aircraft noise and make flying more efficient. It features vibration dampeners on the engines, and the cockpit is outfitted with special iPads with new types of navigation tools pilots can use to plot more direct routes.

Using fuel cells in aviation is problematic because hydrogen is highly flammable. Boeing says airborne fuel cells are likely decades away. Before the technology can be used effectively, the aircraft manufacturer says ways need to be found to make the system safe -- possibly by keeping the fuel cell's hydrogen outside of the pressurized part of the plane, such as in the tail behind the rear pressure bulkhead.

Joe Breit, an associate technical fellow at Boeing who has been working with Japan fuel-cell developer IHI for about six years, believes the technology holds promise for aviation. The experimental fuel cell on board the American Air test jet can generate 15 kilowatts of electricity, enough to power a typical three-bedroom house.

That amount of power could run the 737's galleys, ovens and coffee makers. Eventually, it could provide half the power on the airplane.
On so called fly-by-wire jets like the 777 and 787 that can consume up to a megawatt of electrical power during a trip, the environmental leverage from fuel-cell technology would be even greater.

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