Solar Impulse 2: Biggest challenge of circumnavigation?
Two pilots are hoping to fly into the record books by circumnavigating the planet in a solar-powered plane.
Andre Borschberg and Bertrand Piccard are taking it in turns to fly the Solar Impulse 2 on its five-month journey.
The longest single leg will see one of them fly solo non-stop for five days and nights across the Pacific Ocean between Nanjing, China and Hawaii, a distance of 8,500km (5,270 miles).
BBC News looks at the conditions and challenges the pilots will face.
Video produced by Sara Barman