The small airplane is too dirty for an environmentally threatened world. That’s not the view from eco-activists, but from some of the leading lights in general aviation—the category encompassing small planes such as Cessnas flown by citizen pilots. “At some point, some environmental group is going to figure out that small aircraft fly leaded fuel,” said Mark Moore, NASA’s personal air vehicle program manager, to a meeting of engineers, aviation advocates and a billionaire corporate titan with his own private jet. Their goal, however, is not to bury private aviation, but to remake it as the greenest form of personal transit.

The second annual Electric Aircraft Symposium was held in late April at the most fitting location—a hotel conference room a stone’s throw from San Francisco airport, the gateway to Silicon Valley. (Advanced electronics will be as crucial to aviation as it is to Google or Intel.) The list of benefits starts with efficiency. Three hyper-technical presentations at the meeting (despite being packed with impenetrable terminology) made one point clear: electric motors are virtually magical. While it’s remarkable for an internal combustion engine to achieve anything over 20 percent efficiency, electric motors commonly hit well over ninety. Hook that system up to a fuel cell or battery charged by wind or solar power, and the filthy personal airplane becomes the greenest form of transportation—maybe even beating any future winner of the $10-million dollar, 100-mile-per-gallon Automotive X-Prize.

“When your 100 mpg car is stuck in traffic and a 100 mpg airplane whizzes overhead, you’re jealous,” said Brien Seeley, the conference organizer. Seeley isn’t jumping on the now-fashionable green bandwagon; he’s been obsessed with green flight for decades. It started in 1981, when he and his wife, Anne, were on a cross-country trip, flying in one plane while Anne’s parents were in another. At one of the airports along the way, Seeley challenged his father-in-law, a fellow ophthalmologist, to a battle of fuel-efficiency. Shortly afterwards, and despite his full-time job as a surgeon, Brien Seeley, together with Anne, founded the Comparative Aircraft Flight Efficiency Foundation (CAFE), a nonprofit organization that evaluated fuel-efficiency and other performance aspects of personal aircraft.

Many of those planes have been homebuilt models, part of a phenomenon that took off in the 1970s, when hobbyists began buying kits designed by aviation engineers such as Burt Rutan. In 2004, Rutan’s team won the $10 million Ansari X-Prize for building the first civilian craft to take passengers into space twice within two weeks.