HONOLULU – A solar-powered plane has passed the “point of no return” in its second bid at making a record-breaking flight across the Pacific Ocean.

Solar Impulse took off from Japan’s Nagoya Airfield on Sunday. The journey to Hawai‘i was expected to take approximately 120 hours.

The team had spent nearly two months waiting for clear weather to cross the Pacific, and then a fast developing cold front forced the plane to make an unscheduled landing in Japan earlier this month.

“Andre Borschberg has passed the point of no return and must now see this five days five nights flight through to the end,” Solar Impulse said on its website.

The pilot now no longer has the option to turn around and return to Japan, if the weather forecast changes.

If the pilot succeeds, it will be the longest-duration solo flight in aviation history, as well as the furthest distance flown by a craft that is powered only by the sun.

The Pacific crossing is the eighth leg of Solar Impulse’s journey around the world.

But this stage has proven to be the most difficult, and has been hit by weeks of delays.

Swiss pilot and Solar Impulse co-founder Andre Borschberg, who is flying the experimental single-seater craft, departed Nagoya on Sunday with meteorologists confident they have found a weather window to allow the five-day, five-night crossing to Hawaii.

A spokesperson said that the plane would be heading straight out across the Pacific.

The experimental craft –which has 17,000 solar cells – is powered only by the sun.

Once over the ocean, if it fails to soak up enough rays to fully charge its batteries and make it through the night, the pilot could be forced to bail out.

Borschberg has been trained for that eventuality. He has a dinghy and enough supplies for several days while he waits for the team to identify a vessel to go pick him up.

But, of course, the team hopes none of this will be necessary.

Borschberg will spend the duration of the flight strapped into his seat in a cockpit that is about the same size as a telephone booth.

He will only be allowed to take 20-minute cat-naps, but says he will use yoga and meditation to make his journey more comfortable.

If this flight succeeds, the plane will continue its journey around the world, with co-pilot Bertrand Piccard taking the controls for the next Pacific crossing from Hawai‘i to the US mainland.

The plane will then continue across North America, before attempting to fly over the Atlantic.

However, the build-up of delays could impact on the later stages. Ideally, the plane needs to cross the Atlantic before August, when the hurricane season reaches its peak.