British airline Virgin Atlantic on Tuesday operates the first transatlantic flight powered entirely by Sustainable Aviation Fuel (SAF), but environmental groups criticised the event as "greenwashing".
The flight will leave London's Heathrow airport at 1130 GMT bound for New York's JFK.
It is the first time that SAF will be used "in both engines, by a commercial airline, for long-haul flight", the airline said in a statement.
However, the Boeing 787 plane equipped with Rolls-Royce engines will not carry any paying passengers or cargo.
SAFs are produced from renewable biomass and waste resources and can be used in jet fuel to a maximum of 50 percent, having been blended with kerosene, in modern aircraft.
They are seen as the main tool for decarbonising the aviation sector over the coming decades, but the technology is still in its infancy and production remains very expensive.
Also, they are used in combustion engines that still generate carbon dioxide, with decarbonisation taking place further upstream by reusing plant matter instead of extracting hydrocarbons.
The UK government last December announced that it was providing up to GBP1 million ($1.26 million) in support of the project, led by Virgin in collaboration with the University of Sheffield, US aircraft manufacturer Boeing and British engine manufacturer Rolls-Royce.
Environmental group Stay Grounded called the operation "greenwashing" -- a term used for companies that use deceptive claims to convince the public that their products or operations are environmentally friendly.
"While public focus is on this one seemingly green flight, there are 100,000 daily flights using fossil fuels," said Magdalena Heuwieser, from the Stay Grounded network.
Finlay Asher, an aerospace engineer who has worked for Rolls-Royce, quoted by Stay Grounded, said that the production process was a "technological dead-end" that "can't be sustainably scaled beyond a few percent of existing jet fuel use".
Greenpeace also criticised the event, with its chief scientist Doug Parr warning that "the two potential sources of genuinely sustainable aviation fuel are both severely limited in scale".
"The waste used as feedstock for the bio-kerosene in this flight is not available in quantities large enough to make a big impact on aviation's emissions.
"And the CO2 from Direct Air Capture and green hydrogen from electrolysis -- both used to make e-kerosene -- are very expensive to produce.
"The only effective way to deal with aviation emissions in the short term is by tackling demand, and any suggestion otherwise is just pie in the sky," he added.
The flight comes two days before the UN's COP28 climate conference in Dubai, where the future of fossil fuels will be hotly debated.
