BBC: The zero-fuel aeroplane, Solar Impulse, has left the Egyptian capital, Cairo, on the last leg of its global tour. The aircraft should take about 48 hours to reach Abu Dhabi, UEA - the place it began the circumnavigation in March 2015. Pilot Bertrand Piccard is at the controls one final time. His flight ought to be fairly straightforward, although his team has some concerns about how the heat in the Middle East may affect the plane. Mr Piccard is likely to have to spend a lot of time at high altitude...