The Solar Impulse 2 aircraft has set off from New York to cross the Atlantic, one of the toughest stages of its attempt to fly around the globe using solar energy.
The pilot, Bertrand Piccard, will attempt to reach Seville in Spain in about 90 hours.
He was due to take off on Sunday but was delayed by bad weather.
Mr Piccard will only be able to take short naps while the plane is in flight.
This will be
“the longest distance we have had to fly this year,”
the Solar Impulse team said.
Mr Piccard, a psychiatrist, is sharing the 35,000km (22,000 mile) round-the-world journey with Swiss entrepreneur Andre Borschberg.
The Impulse, which has the wingspan of a Boeing 747, is covered in 17,000 photovoltaic cells to capture the sun’s rays.