Solar Impulse in holding pattern ahead of historic sunset landing in Hawaii

The solar-powered plane is now at an altitude of about 500m as it waits for the sun to rise before its scheduled landing in Hawaii at 8pm UAE time.

Solar Impulse is awaiting sunrise before attempting the tricky landing in Hawaii at 6am local time and 8pm UAE time. AP

The countdown is on for Solar Impulse 2 landing in Hawaii following its historic, non-stop flight from Japan using only solar power.

Swiss pilot Andre Borschberg is currently resting in 20-minute increments in preparation for touchdown, which is expected to take place 6am local time in Kalaeloa, Hawaii (8pm on Friday in the UAE).

"It's going to be a very, very exciting day," said Conor Lennon, host of Solar Impulse TV, which is broadcasting live from the mission control centre in Monaco at solarimpulse.com. "We have pushed it to the absolute limit. We are confident we will make it to Hawaii."

As of 6.20pm UAE time, Mr Borschberg had covered 8,138km, or 98 per cent, of this leg of the journey, and was flying at about 50kph at an altitude of 487m in a holding pattern until sunrise.

Viewers can watch the live transmission and listen as Mr Borschberg communicates with mission control inbetween rest periods today as he travels the last 147km.

The pilot has spent more than four days flying over the Pacific Ocean since taking off from Japan on June 28 for the eighth, and longest, leg of the around-the-world flight that began in Abu Dhabi in March and ends in the capital in August.

"This flight is demanding and challenging, particularly given its duration: 120 hours on solar power only," according to solarimpulse.com. "It is a feat never accomplished before in the world of aviation."

The zero-fuel plane is powered by the sun during the day. Solar energy is also used to recharge the batteries needed to operate the plane at night. Mr Borschberg has three oxygen tanks left, although he only needs one to complete this leg of the mission. His diet is made up of specially formulated snacks he eats several times a day to slow down his muscle loss in high altitude.

“During the fourth day I felt very tired, having climbed the equivalent altitude of Mount Everest four times,” Mr Borschberg tweeted on Friday morning. “It is delicate to maintain a balance between my energy and the energy of the aircraft.”

In advance of landing, he is performing holding patterns, enabling him to rest and store up energy for the high-risk landing, according to organisers.

Earlier on Friday, the flight got rather bumpy as Mr Borschberg flew through unexpected cloud coverage.

“Because we have an overcast situation, it was quite turbulent for a moment,” an engineer said in a briefing aired live on Solar Impulse TV. “But, generally speaking, the pilot is in quite good health status, he has had a rest of approximately two-and-a-half hours in the night, his mood is OK until now.”

The extra power needed to fly over the clouds took a bit of a toll on the plane’s batteries, which are just under 50 per cent, the engineer said.

“For the energy status, we are now much lower than planned but we gained altitude so we took in full power to climb to avoid this turbulent layer,” she said. “But now, as I said before, we have started the descent and it should be fine.”

The landing has been planned for sunrise to give Mr Borschberg a chance to rest, while his family, media are supporters gather at the airport in preparation for celebration.

“The atmosphere is very good around here, quite relaxed given them circumstance,” added Mr Lennon.

“We have to stay quite concentrated because landings and takeoffs are very, very important and very, very complicated for any plane, so we want to make sure that Andre Borschberg is as relaxed and concentrated as possible.”

In its record-breaking mission to circle the world in the single-pilot propeller plane without the use of fuel, the project aims to raise awareness of clean and alternative energy.

“Always feels good to break records but it is not the goal of @solarimpulse #futureisclean,” Mr Borschberg tweeted. “We are not going #RTW with @solarimpulse to break records but to demonstrate that clean technologies can really change the world!”