image via (cc) flickr user seier

For the past several months, aviation aficionados and green-energy enthusiasts alike have been eagerly following the progress of the Solar Impulse “perpetual endurance” airplane as it attempts to circle the planet using nothing but energy provided by our sun. While that craft is, at present, a single, custom-built flyer, and not the sort of thing likely to replace an airline’s current fleet of jets any time soon, it does offer a tantalizing glimpse at a possible future for air travel—a future in which our skies fill with planes that are safe, efficient, and entirely ecologically friendly. Unfortunately, the Solar Impulse is currently grounded in Hawaii, following damage to its solar batteries. But while the Impulse may not be slated to return to the air until sometime in 2016, there’s been another major milestone in green aviation in the meantime. One that’s considerably more down to Earth.