Andre Borschberg was manning the controls this morning as the experimental aircraft, now deep into its history-making circumnavigation of the globe, took off shortly after 5 a.m.
Borschberg's co-pilot, Bertrand Piccard, was chief pilot on the previous leg of the journey, a three-day trip between Hawaii to Mountain View, in the heart of Silicon Valley.
Solar Impulse 2 is powered by 17,000 wing-mounted solar cells which provide energy for its engines and recharge its batteries for nighttime flight.
After Phoenix, the plane will make two more stops in the United States before crossing the Atlantic.
The aircraft took off from Abu Dhabi in the United Arab Emirates in March 2015, and has since made stops in Oman, Myanmar, China and Japan.
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