The pilot of a solar-powered aircraft attempting a round-the-world voyage has said the longer the plane is grounded in Japan the closer the project will come to failing this year.

Swiss adventurer Andre Borschberg said the Solar Impulse 2 will continue its journey from Nagoya Airport as soon as the weather improves, but he said it now needs a clear run if it is to complete the journey as planned.

“We have question marks,” Borschberg told The Japan Times on Wednesday. “We certainly do not have a lot of time in reserve. We ate our margin, to be totally honest.

“There may be a situation when we are too late maybe to cross the Atlantic,” he added, in which case the project would have to be suspended until next year.

“All will depend on how fast we can go from here on this leg and afterwards.”

On June 1, poor weather forced the Solar Impulse to make an unplanned landing at Nagoya Airport, also known as Komaki, part way through a hop from Nanjing, China, to Hawaii.

The flight from Nagoya to Hawaii will take five days and five nights, and predicting such a period of calm weather more than a day or two ahead of time is “guesswork,” Borschberg said.

“Impatience is something we have to manage,” he added.

He said the Solar Impulse technicians and support staff have embraced their unscheduled visit to Japan with joy. They are staying at a hotel near the airport, he said, but have made trips to the countryside, Kyoto and Tokyo.

“People are enjoying it, eating Japanese food, and with a big smile because people are really nice to us,” he said.

Borschberg said he has used his own downtime to revisit the Tokyo neighborhood he knew 30 years ago, when he spent a year in the capital on a posting with McKinsey & Co.

“My daughter was going to a school which is just across from the house where we used to live in Azabu-juban, and I went to visit the school again, so it brought memories back,” he said.

Borschberg paid tribute to Japanese authorities for their efforts to accommodate the plane and its staff. He singled out customs officers for swiftly expediting the transfer of a large amount of cargo from Central Japan International Airport to the tarmac at Komaki, and officials at Nagoya Airport for meeting the plane’s unorthodox requirements.

“We had to bring in more than 300 tons of concrete. This is something like 40 trucks,” he said, describing the material as ballast to anchor the inflatable hangar that protects Solar Impulse from the weather.

“First of all, they helped us to find it in a few hours. Second, they allowed us to bring it on the airport. So I tell you, the help we got was really great.”

Borschberg is enthusiastic about the project’s achievements so far and remains upbeat about the plane’s potential to reach Abu Dhabi, its starting point.

“I guess this leg is the most difficult one because . . . it is the longest in terms of distance and duration. We also have little experience” of handling a nonstop flight lasting several days, he said.

“That’s why we call this one the moment of truth, because it’s pure discovery, it’s pure exploration, it’s true pioneering pride.”