Amateur pilots buy approximately 1000 small aircraft each year, according to Richard Golaszewski, executive vice president of GRA, an aviation consultancy in Jenkintown, Pa. Carl Dietrich, Terrafugia’s chief executive, estimates that the market is slightly larger and says he is confident he will sell “a couple hundred” Transitions annually in each of the next few years—which would be quite an accomplishment for an unknown, untested design team.

Priced at US $148 000, the Transition falls significantly outside the $50 000 to $100 000 price range of new light-sport aircraft. By opting for an $80 000 Rans S7, for example, a pilot could, for the same amount of money, choose to spend the remaining $68 000 on cab rides, rentals, or a new superloaded Chevy Corvette.

Dietrich, who is working on a Ph.D. in aeronautics and astronautics at MIT, won the 2006 Lemelson-MIT Student Prize for the Transition’s design. Using the $30 000 award, Dietrich launched Terrafugia that spring, with the hope that his vehicle would make noncommercial air travel significantly easier.

Dietrich is not alone in his belief that the airspace over the world’s sprawling metropolises is clogged, with little room for growth. Many say that regional airports provide a convenient outlet and that the main obstacle impeding their use is the trouble of getting a pilot to and from the airport. According to Dietrich, only one third of the 5000 general-aviation airports in the United States have taxi or car-rental facilities nearby. With the Transition, Terrafugia’s engineers dream that personal air travel will finally become mainstream. “Comparing two different light-sport aircraft, one standard and the Transition, there’s a lot of draw to an airplane you can keep in your garage,” Dietrich says.

Even if Terrafugia meets its goals, the air expressways of Back to the Future and “The Jetsons” will remain the stuff of daydreams. Boeing and NASA have independently analyzed the feasibility of personal air vehicles and each concluded that a wider problem hinders individual air travel: the absence of support structures to make increased traffic safe and reliable.

“After an initial look at designing a vehicle, we decided we were missing the big picture,” says Lynne Wenberg, a senior manager at Boeing’s Phantom Works research division in Seattle. More traffic at small airports necessitates more air traffic management, control towers, and systems to help lower-skilled pilots land in bad weather. NASA aviation expert Bruce Holmes argues that small airports would have to undergo a ­massive, ­government-supported update. “This is really not going to be a one-company development,” Holmes says.

At the moment, however, the U.S. National Highway Traffic Safety Administration holds sway over Terrafugia’s future. If the agency decides the Transition is sufficiently carlike, Terrafugia will have to comply with crashworthiness standards that would add weight to the car and further complicate the design, potentially dooming it.

Rather than abandon the light-sport aircraft idea, Dietrich says he would resort to a three-wheeled version, to be classified as a motorcycle, which has looser safety requirements. Some aircraft designers, including NASA’s Holmes, actually prefer the idea of a flying tricycle, because it is less likely to become mired in traffic safety restrictions. But Dietrich is reluctant to move in that direction, hoping to keep the vehicle in a more familiar shape.

For the time being, the flying car stays tethered to the shop, a clunky compromise whose time may never come.