A former aeronautics and Formula 1 engineer with the seemingly crazy idea of building cars that run on compressed air has convinced a European airline to use his "AirPods" to ferry passengers around airports in France and Amsterdam.

Guy Nègre has been tinkering with compressed air vehicles for about 20 years, but he and his company, Motor Development International, have done little more than build some prototypes that have garnered interest from the likes of India's giant automaker Tata Motors and an American startup called Zero Emissions Motors.

With Air France/KLM officials announcing they will give the vehicles a six-month test in the rough-and-tumble environment of two busy airports, Nègre may finally prove his vehicles are more than hot air.

The airline says AirPods will carry passengers between departure gates at Charles De Gaulle Airport in Paris and Schiphol Airport in Amsterdam. The AirPods slated for airport duty will be the first operational version of MDI’s Air Car concept, which is vying for the Progressive Automotive X-Prize.

The AirPod carries four people in a vehicle that is about 6 feet long and weighs roughly 450 pounds. Its single-piston engine is driven by compressed air. The tank holds 175 liters of compressed air, according to Zero Pollution Motors, and can be filled to 350 bar (5,076 psi!) in as little as 90 seconds. That's enough to give the AirPod a range of about 135 miles and a top speed of 43 mph.

MDI won't be building Air Cars. Rather, it's counting on licensing agreements with Tata and Zero Emissions Motors to bring the world Air Cars by 2010 or 2011. If the idea of a zero-emissions car that runs on air sounds too good to be true, we share your skepticism.

Besides the continuing production delays, a promised top speed of 90 MPH and range of 848 miles for the AirFlow model seem — to put it mildly — over promise. Tata isn't convinced the technology is quite ready for prime time, and Andrew Frank, a professor of mechanical engineering at the University of California at Davis, told The New York Times, “It's a losing game because the efficiency is just not there.”

Everything about the Air Car seems to suggest an “It’s a Small World”-sort of innocence. MDI's industrial model for “micro production” imagines incredibly green cars being produced all over the world at fractions of typical costs. But none of the technology has ever been proven, which is why the tests of the AirPod at Schiphol and de Gaulle airports are so important. Yet even the limited scope of the AirPod’s test run at two airports seems to speak to a major lag in a technology that may fill little more than a tiny niche.

A car that runs on air is a cool idea in theory. But as the battle to replace gas heats up, it looks the AirCar could be little more than vaporware.

Photo courtesy MDI