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Five days over the Pacific

From The Field
Five days over the Pacific

Written by Bruno Boehm and Marie Perez of the Solar Impluse 2 team.

It’s hard for us to realise that it’s been a year already. A year since André Borschberg accomplished a five-day-and-night flight over the Pacific Ocean with Solar Impulse 2 (Si2). A year since he beat the world record of longest solo flight and achieved the round-the-world journey. And now that Bertrand Piccard crossed the Atlantic Ocean a few days ago – meaning that we’ve conquered the two largest oceans in the world – we’d like to tell you the story of this amazing jump into the unknown from Nagoya, Japan to Hawaii.


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On June 28th 2015, André took off from Nagoya without a single drop of fuel on board Si2. Not because he’d forgotten to fill the tank, but because our experimental aircraft is a solar plane which flies using the energy collected by its 17,248 solar cells during the day, and the energy stored in its four batteries during the night. After an unplanned landing in Nagoya due to extreme weather conditions, and several weeks of waiting for the right flight window, André had finally been cleared for takeoff by the Mission Control Center (MCC) in Monaco. A sensational moment for the whole team. (Here’s a video of the flight plan.)

At first, everything was going well. The sun was out, the plane was flying and the pilot was in good spirits. But suddenly, an alarm went off in the  Mission Control Center.

‘While I rested a few hours after takeoff, I detected a failure in the system supervising the airplane,’ said pilot André Borschberg. ‘With a flight lasting at least five days and nights, especially as I was alone in the cockpit, this system was of crucial importance. As the system was still not functioning properly when I reached the point of no return, all my engineers told me to return to Japan to fix the problem. But it was the first time that the weather over the Pacific was extremely favourable after two months of waiting and delaying our departure. So I looked at the question differently and found that the overall mission risk was reasonable, that I would find ways to compensate for the failed equipment. I decided to continue, which created a huge emotional reaction within the team. But it was the only way to make it possible. It was a tough decision but I felt deep down that it was the right moment.’

Bertrand Piccard was at the MCC at the time and agreed with André, but they had to discuss and evaluate the risks with the team before taking the final decision. The atmosphere was tense in Monaco, and the rapidly approaching point of no return didn’t help.


Five days over the Pacific

Bertrand said: ‘There was a deep division in the team. The engineers who built the aircraft wanted to protect their baby by scrupulously respecting procedures, and we all understood that. The rest of the team wanted to save the project – with the approaching rainy season and administrative investigations triggered by an emergency return to base, returning to Nagoya would rule out a later take-off. You can’t cross an ocean without losing sight of the coast, even if it’s a frightening thought. The whole team had to learn that lesson… Exploration is a leap into the unknown. As André flew on towards Hawaii, I didn’t know what would happen, but I was firmly convinced that this was the right decision. It’s not every day that you have an appointment with destiny.’

André was prepared for this kind of situation. As an explorer, he knew that the unknown includes risks and having to take critical decisions which make the difference between success and failure.

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Once the decision to continue had been made, André began settling in to the 3.8m3 unpressurised and unheated cockpit – the flight was on! He enjoyed the first sunrise of the flight: ‘The aircraft now receives enough sun to carry on flying while at the same time charging its batteries, that’s the beauty of renewable technology!’ There was no getting bored up there: he tidied his new home, took notes and read, stretched, ate, put his oxygen mask and altitude clothes on as the plane rose higher and higher. In terms of flight profile, he would have to climb to 28,000ft – the altitude of Everest – each day in order to charge the batteries, and then glide back down to save energy and make it to the following morning. And André knew that he would not have to do it alone, that thousands of people would be following him and encouraging him live on, thanks to the cameras placed inside the cockpit and on the plane.

The next day also brought its share of emotions. After 44 hours 10 minutes and 3,167 km of flight, André broke the world record for longest solar flight. A record he would continue beating all along his flight seeing as he’d only completed 37% of the journey to Hawaii.

Though Solar Impulse set several world records over the years, the team never forgot its true goal: to spread the message that clean technologies can change the world. That’s what fueled their motivation and sleepless night watching over the plane.

July 1st: third day in the air, and 2⁄3 of the flight had already been completed. After the initial stress of the failing system, it now seemed possible that André would make it safe and sound to Hawaii. Only about 40 hours to go according to the mission engineers. André felt less tired than the morning before and ready to tackle the first day of this new month.

Later on he discovered the notebook hidden in the cockpit by the team before takeoff. Inside: messages of encouragement and hope to spur him on. After over 5,000km of flight, the team was wondering if he’d ever find it…

Fourth day of flight and second world record broken! That of longest solo flight, after 96 hours spent in the air. The previous record has been set by Steve Fossett in 2006. A nice reward after the longest and most tiring night of André’s flight. The weather had been a little turbulent, and he had not been able to take as many 20-minute naps – his resting technique when flying Si2 – as usual. Nevertheless, he was in high spirits as the reliability and endurance of the plane’s clean technologies were being proven which each hour that went by. Only about 28 to go according to the MCC.


“As I started getting closer to the Hawaiian Islands, I began hearing the first sounds on the radio between the airplane and the Air Traffic Control centers. And while I could not see the islands, I knew they were not far away. These radio frequencies were silent during the previous 4 days and nights as I was too far from other airplanes or any airport. It reminded me that navigators would try to spot birds when they thought they were within 100 miles of an island. By looking at how and where these birds would fly, they would then understand if they were moving away from or approaching an island. I could only imagine how happy they must have been to see the first birds dancing in the air over their ship, similar to how happy I felt when I heard the first radio chatter and knew I was slowly reaching my destination.”

On July 3rd, after a flight of 117 hours and 52 minutes and a lot of emotions, André touched down on the Hawaiian airport of Kalaeloa. The MCC broke into thunderous applause while the on-site team welcomed the pilot with laughter and tears.

Five days over the Pacific

André said: ‘I feel exhilarated by this extraordinary journey. I climbed the equivalent altitude of Mount Everest five times – once each day – without much rest. The MCC, my eyes and ears, was battling to give me options for rest and recovery, but also maximising the aircraft’s energy levels and sending me trajectories and flight strategies simulated by computer. This flight successfully validates Bertrand Piccard’s vision after his round-the-world balloon flight, to achieve unlimited endurance in an airplane without fuel.’

Bertrand added: ‘What André has achieved is extraordinary from the perspective of a pilot. But furthermore, he also led the technical team during the construction of this revolutionary prototype. It is not only a historic first in aviation, it is also a historic first for renewable energies.’

It took them 12 years of hard work, but Bertrand and André have finally proved that it is possible to fly perpetually, relying only on the sun’s energy and on clean technologies. And if a solar airplane can fly for days and nights without a drop of fuel, then doesn’t that show the technologies inside it can be used on the ground to reduce our energy consumption?


To learn more about Solar Impulse flights around the world, back to Abu Dhabi, check out the mission updates. Sidetracked will be featuring the latest leg very soon.