It would emit no carbon dioxide, the main gas blamed for global warming, or other pollutants, leaving just a trail of water. It would also be almost completely silent. The hitch? It would fly at only 70mph.

The decision to develop the plane comes amid growing concern over high carbon dioxide emissions from passenger jets.

Boeing is working with Intelligent Energy, a British fuel cell designer. It hopes the two-seater aircraft will make its maiden flight in the next 12 months.

“What we are designing is a demonstrator aircraft to see if it can be done,” said Boeing. “This technology is in its infancy but it has great potential.”

The aircraft is based on the Diamond Dimona, an Austrian plane chosen for its light weight. Boeing engineers in Madrid have stripped out its fuel tank, replacing it with a bottle of compressed hydrogen that will feed into a fuel cell.

There, the hydrogen will be chemically combined with oxygen from the air to generate power. This will then be fed to an electric motor to turn the propeller.

The system is mechanically simple. Fuel cells have no moving parts and run silently. They tend, however, to be bulky and expensive, which is why their use has never become widespread.

Dr Jon Moore, director of communications at Intelligent Energy, based in Loughborough, Leicestershire, said technological advances were now making such devices far lighter and cheaper, but aviation remained the biggest challenge.

“The secret lies in making a fuel cell powerful enough to get an aircraft off the ground and to keep it climbing,” he said. “That takes a huge amount of energy and it is a big obstacle.”

Boeing has overcome this by backing up the fuel cell with batteries that provide extra power for take-off and then recharge while the aircraft is cruising.

The Boeing project will be the first manned fuel cell- powered aircraft. Last year AeroVironment, a Californianfirm, flew an unmanned surveillance plane, the Global Observer, which was powered by a fuel cell.

Even if Boeing succeeds with its aircraft it will take many years to scale it up for commercial use.

Another big problem is finding a supply of “green” hydrogen. Most commercially produced hydrogen is synthesised in refineries from fossil fuels such as natural gas. Critics call this “black hydrogen” because carbon dioxide is generated as a by-product, cancelling out many of the potential benefits.

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