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 USA, 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