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.
It is the first ever attempt to cross the Atlantic in a purely solar-powered aircraft.
Mr Piccard takes short naps while the plane is in flight.
The Atlantic crossing will be “the longest distance we have had to fly this year,” the Solar Impulse team said.
The flight was supposed to begin on Sunday but was delayed by bad weather.
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.
It landed at New York’s John F. Kennedy International Airport on 11 June after a five-hour flight from Lehigh Valley in Pennsylvania.
The record attempt began on 9 March 2015 in Abu Dhabi, and has taken the aircraft across Asia and the Pacific to the United States.