There can be many delays along the road from concept to certification. For instance, government officials and the designers have had to determine which regulations — aircraft or automotive — take precedence when the vehicle in question is both.

In the United States, development of the flying car was given some breathing room eight years ago when the F.A.A. created a new classification, the light-sport category, to encourage the design of small, easy-to-fly aircraft. To meet the light-sport definition, the aircraft must have a single engine and an unpressurized cabin, have one or two seats and weigh no more than 1,320 pounds; maximum air speed is limited to 138 miles per hour.

http://www.nytimes.com/2012/04/29/automobiles/before-flying-car-can-take-off-theres-a-checklist.html