Image copyright Solar Impulse Image caption Andre Borschberg flew over the pyramids before landing

The Sun-powered aircraft Solar Impulse has finished its penultimate flight, landing in Egypt's capital, Cairo.

It took off from the Spanish city of Seville at 04:20 GMT on Monday, taking just over 48 hours to make the trip.

The zero-fuel aircraft is now in the home straight of its bid to circumnavigate the globe.

Its final stop is Abu Dhabi, where the challenge began in March 2015. The two pilots sharing flying duties are each taking one more turn at the controls.

Andre Borschberg did the Seville-Cairo stage, soaring over the pyramids and the Sphinx at Giza before landing.

"The final approach to Cairo was a bit tough but I made it," he tweeted.

Image copyright A Borschberg Image caption The Swiss adventurer said he celebrated flying over the pyramids by eating Swiss cheese

Bertrand Piccard will complete the challenge by taking Solar Impulse back into the United Arab Emirates in the next few days, depending on the weather.

Towards the end of the flight, it was the first time the plane's battery levels had gone under 30%, mission managers said.

They organised to land in Egypt, where they were greeted by the country's ministers of aviation and energy, in the morning when the winds and temperatures were most favourable.

Image copyright Solar Impulse Image caption Solar Impulse flying over Torresol Energy’s Gemasolar Thermosolar Plant after taking off from Seville

Before taking off from Seville International Airport, Mr Borschberg said he inevitably felt the emotion of making his last journey in the plane.

"It's meaningful obviously because it's my last flight in this round-the-world epic. I've started to think about it. I'm happy that we get close to the end but also prudent knowing that it is not done yet. I have to stay really focussed."

The penultimate leg crossed seven countries, negotiating some very busy air routes.

The slow-moving plane also had to take account of a number of military operations in the Mediterranean/North Africa region.

For Mr Piccard, reaching Egypt is an important milestone for the project he founded.

It was in the North African nation that he landed 17 years ago in Breitling Orbiter 3 - the first balloon to make a non-stop, round-the-world flight.

"We arrived there with so little fuel left - you know, the propane gas you have to burn in your envelope to stay airborne. I landed there with less than 1% of our reserves, and I was really scared to fall short of gas before the end. And that's when I said I want to fly around the world again but with no fuel," the Swiss adventurer said.

Mr Piccard and Mr Borschberg have been working on the Solar Impulse project for more than a decade.

Their plane is wider than a 747 jumbo jet but weighs just 2.3 tonnes, which poses some unique challenges:

The aircraft is very sensitive to the weather conditions

But its solar cell and battery efficiency is very high

This means it can stay aloft for many days and nights

The pilot is permitted only catnaps of up to 20 minutes

The cockpit is little bigger than a public telephone box

LEG 1: 9 March. Abu Dhabi (UAE) to Muscat (Oman) - 772km; 13 Hours 1 Minute

LEG 2: 10 March. Muscat (Oman) to Ahmedabad (India) - 1,593km; 15 Hours 20 Minutes

LEG 3: 18 March. Ahmedabad (India) to Varanasi (India) - 1,170km; 13 Hours 15 Minutes

LEG 4: 18 March. Varanasi (India) to Mandalay (Myanmar) - 1,536km; 13 Hours 29 Minutes

LEG 5: 29 March. Mandalay (Myanmar) to Chongqing (China) - 1,636km; 20 Hours 29 Minutes

LEG 6: 21 April. Chongqing (China) to Nanjing (China) - 1,384km; 17 Hours 22 Minutes

LEG 7: 30 May. Nanjing (China) to Nagoya (Japan) - 2,942km; 1 Day 20 Hours 9 Minutes

LEG 8: 28 June. Nagoya (Japan) to Kalaeloa, Hawaii (US) - 8,924km; 4 Days 21 Hours 52 Minutes

LEG 9: 21 April. Kalaeloa, Hawaii (US) to Mountain View, California (US) - 4,523km; 2 Days 17 Hours 29 Minutes

LEG 10: 2 May. Mountain View, California (US) to Phoenix, Arizona (US) - 1,199km; 15 Hours 52 Minutes

LEG 11: 12 May. Phoenix, Arizona (US) to Tulsa, Oklahoma (US) - 1,570 km; 18 Hours 10 Minutes

LEG 12: 21 May. Tulsa, Oklahoma (US) to Dayton, Ohio (US) - 1,113 km; 16 Hours 34 Minutes

LEG 13: 25 May. Dayton, Ohio (US) to Lehigh Valley, Pennsylvania (US) - 1,044 km; 16 Hours 47 Minutes

LEG 14: 11 June. Lehigh Valley, Pennsylvania (US) to New York (US) - 230km; 4 Hours 41 Minutes

LEG 15: 20 June. New York (US) to Seville (Spain) - 6,765km; 71 hours 8 minutes

LEG 16: 11 July. Seville (Spain) to Egypt (Cairo) - 3,745km; 48 Hours 50 Minutes