Weather delays most challenging leg of Solar Impulse 2 flight

Weather delayed the most challenging leg of Solar Impulse 2's landmark flight around the world powered only by the sun.

The single-seater aircraft was expected to take off from Nanjing, in eastern China, for the 8,500 kilometre (5,270 mile) flight over the Pacific Ocean to the US island of Hawaii in the early hours of the morning.

However, the much-anticipated seventh and longest-section of the maiden solar-powered global circumnavigation was delayed once again due to concerns about weather conditions.

"The flight that we've been looking forward to tonight is not going to happen," Solar Impulse spokesman Connor Lennon said in a video post on the group's YouTube channel.

According to mission director Raymond Clerc, with the cloud cover over Nanjing and the Sea of Japan take-off would have been difficult and the journey would have stretched over seven days and seven nights, two more than originally planned.

"We have big problems that added (together) make the risk too high," he said in the video.

He added, meteorologists were studying weather conditions and would be able to tell in a few hours whether the takeoff would happen in the next couple of days.

Swiss entrepreneur and engineer Andre Borschberg (l) and Swiss psychiatrist and balloonist Bertrand Piccard

Swiss entrepreneur and engineer Andre Borschberg and Bertrand Piccard had been sharing the pilot responsibilities since the plane took off on 9 March in Abu Dhabi, headed for Muscat, in Oman and made the 441 kilometres journey in 13 hours and one minute.

Following a two-and-a-half weeks stay in Chongqing, China, The Solar Impulse 2 landed in Nanjing, China on 21 April. The Chongqing halt was supposed to be an overnight stop, however weather played a huge part there, too, grounding the plane.

The mission would now perforce need to sit out the bad weather over the Pacific Ocean, as much was at stake.

The Solar Impulse website released an update, saying: "The trend of unstable weather in the Pacific has taken a toll for the worse, A combination of factors put this flight at risk, including cloud levels reducing charging capacity and considerable holding and loitering times to get through the front may have forced a seven-day flight, pushing the pilot to excessive extremes."

On 9 March, Borschberg and Piccard launched their first attempt to fly around the world in a plane using only solar power, from Abu Dhabi, in a landmark journey aimed at promoting green energy (See: Solar Impulse-2 starts its first round-the-world flight). arriving in Ahmedabad after a flight of about 15 hours over the Arabian Sea from Muscat in Oman (Solar Impulse 2 lands in Ahmedabad in its first round-the-world flight)