A decisive milestone was reached yesterday as the solar-charged, electric-powered Solar Impulse successfully completed the second-to-last leg of its Across America mission by landing at Washington Dulles International Airport–locally it was Sunday, June 16 at 12:15 a.m.–stimulating renewed enthusiasm for discovery and innovation.

Swiss pioneers Bertrand Piccard and André Borschberg used an unprecedented flight strategy to arrive in Washington D.C. on time despite difficult weather conditions characterizing the cross-country flights. According to the Solar Impulse team, the fourth leg was split into two flights because strong cross- and headwinds would slow down the aircraft, making it impossible for the pilot to reach the nation’s capital within 24 hours, the limit set for the pilot in the cramped single-seat cockpit. The flight plan was modified with Borschberg, who took off on June 14 from Lambert-St. Louis International Airport and flew the aircraft for the first half of the leg to Lunken Airport in Cincinnati, Ohio. After a short pit stop of 14 hours, Piccard flew the second half of the flight, landing at Washington Dulles on June 16 shortly after midnight.

“We have shown that we are capable of coping with challenging meteorological conditions for our weather-sensitive plane and for our ground operations,” said Borschberg. “It has been a succession of fruitful learnings preparing us for the 2015 world tour.”

Engineering consultancy Altran Group (Chalet B30) was responsible for modeling and simulation, system engineering and stabilization augmentation systems for the Solar Impulse. “In 2003, joining the Solar Impulse project was more than just a challenge for Altran because it meant inventing a solar plane,” said Christian Le Liepvre, head of the Solar Impulse partnership at Altran. “The main challenge was to accompany the project to its conclusion: creating a plane that would fly day and night using only solar energy. Altran believed that the impossible could be achieved, and the project teams succeeded.”