The solar plane attempting the first around-the-world flight without fuel completed more than a quarter of its journey to Hawaii from Japan by Monday evening.
As of 7:30 p.m. Hawaii time Monday, the Solar Impulse 2 had finished 27 percent of its journey to Oahu.
The Japan-to-Hawaii portion of the trip is the longest and most dangerous.
Andre Borschberg, CEO of Solar Impulse 2, is piloting the plane alone for the five-day trip.
Ten hours after leaving Nagoya, Japan, Borschberg had reached what the Solar Impulse crew called the "point of no return." Borschberg could not turn back to land in Japan after that point, the Solar Impulse team said.
"Solar Impulse is unable to turn around and return to Japan — from now on, it must land in Hawaii," said Lakshmi Sivaguru, Solar Impulse spokeswoman.
That decision to push forward or head back was pivotal for the entire project, said Solar Impulse 2 co-founder Bertrand Piccard.
"The point of no return for this flight to Hawaii was also the point of no return for the entire project," Piccard said.
Borschberg and Solar Impulse 2 team members were live-tweeting the flight by posting updates about Borschberg’s condition and the plane’s status.
On Monday evening Borschberg had seven of his eight oxygen tanks left, 16 of 18 food rations and 22 of 25 liters of water to help him complete the journey.
The plane, flying an average 35 miles per hour, should arrive in Honolulu either Friday night or Saturday morning, said the Solar Impulse 2 team. Borschberg hopes to land at Kalaeloa Airport in West Oahu.
After two failed attempts to depart Japan, Borschberg successfully took off from Nagoya at 8 a.m. Sunday Hawaii time.
Borschberg and Piccard are taking turns piloting the Solar Impulse 2 across the globe.
Hawaii will be the first destination in the United States for the plane.
The sun will be the only source of energy for the aircraft. The plane’s 72-meter wingspan was built with more than 17,000 solar cells, four electric motors and lithium batteries replacing the need for fuel.
The Solar Impulse team plans to stay two or three days in Hawaii for aircraft maintenance, a news conference and public visits.
After Hawaii the Solar Impulse 2 will fly to Phoenix, then an as-yet-undetermined stop in the Midwest, followed by a landing in New York.