The first time Carl Dietrich brought his flying-car concept to the Experimental Aircraft Association’s annual AirVenture gathering in Oshkosh, Wisconsin, he had only a video to show the aviation geeks who wandered by his modest stall. The following year, he brought the mock-up of a wing. Six years later, in July 2013, he was finally ready to fly the prototype.

As the announcer who introduced the Terrafugia Transition put it: “Ladies and gentlemen, this is one of the most incredible things we’ve seen, ever, here at Oshkosh. Twenty-five minutes ago, this was a street-legal automobile. Now, it’s in the air.”

Pilot Phil Mateer buzzed the crowd while the announcer patched into his cockpit microphone to ask him how it felt up there. “I’m in a car looking down on traffic,” Mateer replied. “And it flies real nice.”

The promise of a mass-produced flying car has taunted aviation enthusiasts for generations, Bloomberg Pursuits magazine will report in its Holiday 2014 issue. However, Dietrich is today closer than anyone since pilot Moulton Taylor’s ill-fated attempt to make the U.S. Federal Aviation Administration–approved Aerocar in the 1950s.

“What Carl and his team are doing is a recreation of that same dream, with another lifetime’s worth of technology, computing, crashworthiness and aerodynamic modeling,” says Jake Schultz, a technical analyst at Boeing Co. and author of ‘A Drive in the Clouds: The Story of the Aerocar.’

$10,000 Deposits

More than a hundred people have paid deposits of $10,000 each for the Transition, which will be capable of 70 miles (110 kilometers) per hour on the road and 100 mph in the sky when it finally comes to market sometime within the next three years. Dietrich is refining details on the third-generation prototype of his $279,000 vehicle before attempting certification by both the FAA, which regulates planes, and the National Highway Traffic Safety Administration, which oversees cars.

A year after that triumphant flight in Oshkosh, Dietrich, 37, sits in his sparsely decorated office at Terrafugia’s modest headquarters behind a Best Western in Woburn, Massachusetts. He says he first proposed a flying car as a doctoral candidate in aeronautical engineering at the nearby Massachusetts Institute of Technology, where he partnered with a pair of Sloan School of Management students and two other engineers (including the woman who’s now his wife) to win second place in the 2006 MIT $100K Entrepreneurship Competition. That same year, Dietrich also won a $30,000 Lemelson-MIT National Collegiate Student Prize, part of which he put toward that initial trip to Oshkosh, where he met his first angel investors and even signed up prospective buyers.

LSA Designation

“We had seven people write us checks for a product that didn’t even exist yet,” Dietrich recalls. “That’s a pretty powerful indicator that people really want this.”

One reason the Transition is further along than any previous flying-car concept is that, in 2004, the FAA created the so-called light sport aircraft designation for planes that weigh less than 1,320 pounds (600 kilograms) and seat no more than two people. LSA manufacturers are given an easier path to market in order to encourage entrepreneurship and innovation in a niche of the industry that has seen very little of either.

“Personal aviation is basically a fun, expensive hobby,” Dietrich says. “My goal is to actually make it useful.”

Solving Problems

Critics say flying cars are unlikely to be both great airplanes and great automobiles. But that misses the point, says Dietrich, who explains the Transition is intended to expand the definition of an airplane, solving a number of persistent problems in the process.

First and foremost is that small planes are virtually useless in inclement weather. If a storm rolls in while you’re flying the Transition, on the other hand, you can simply land at many of the 5,000-plus airports in the U.S. alone, push a button to fold up the wings and hit the road until conditions improve. At home, you can park it on the street or in the typical suburban garage. And it runs on regular unleaded gas, which is cheaper and cleaner than aviation fuel and available at your local service station.

“You’re getting comparable gas mileage to your road car, but you’re going 100 miles per hour over all the traffic,” Dietrich says.

That makes the Transition ideal for weekend jaunts or for salespeople and others whose jobs require regular trips of a few hundred miles—although, at the expected price, even he admits it won’t be within reach of your average salesperson anytime soon.

Endless Refinements

Dietrich rocks back in his chair. “It can be frustrating,” he says of the endless refinements and the pending approvals process, “but I wouldn’t be doing this if I didn’t think we had the potential to inspire a trillion-dollar industry.”

The way he sees it, flying cars are inevitable, and once the first one proves its way in the world, others will follow. Already, he’s at work on a semi-autonomous, vertical-takeoff model.

“I wouldn’t waste my time if I didn’t think we could change the world,” he says.