Solar Impulse 2 is headed to its final destination, Abu Dhabi, with the flight expected to take between 48 and 72 hours
The first solar-powered plane to circle the world took off from Cairo today for Abu Dhabi, in the final leg of its journey.
Swiss pilot Bertrand Piccard was behind the controls of Solar Impulse 2, which can fly for days on only energy from the sun.
"It's a project for energy, for a better world," Piccard told journalists before taking off.
Pilots Piccard and Swiss entrepreneur Andre Borschberg have taken turns flying the plane on its 22,000-mile (35,000-kilometre) trip around the world.
Borschberg piloted the flight's Pacific stage, a 4,000-mile flight between Nagoya, Japan, and Hawaii.
Solar Impulse 2 arrived in Cairo after a two-day flight from Spain, finishing the 3,745 kilometre journey with an average speed of 76.7 kilometres an hour.
It had earlier landed in Seville after completing the first solo transatlantic flight powered only by the sun.
The carbon fibre plane, with a wingspan exceeding that of a Boeing 747 and the weight of a family car can climb to about 8,500 metres (28,000 feet) and cruise at 55-100 kph (34-62 mph).
"The project is a big promotion of clean technologies around the world and the legacy of Solar Impulse is the created international community," Piccard said.
The single-seat aircraft, no heavier than a car but with the wingspan of a Boeing 747, is clad in 17,000 solar cells. During night-time flights it runs on battery-stored power.
It typically travels at a mere 30 miles (48 kilometres) per hour, although its flight speed can double when exposed to full sunlight.