An environmental aviation expert has labelled Virgin Atlantic's sustainable flight as a "gimmick, not a game changer" after its successful journey from London to New York on Tuesday. 

The passenger jet, which flew without paying passengers, with Virgin Atlantic's billionaire founder Richard Branson, the airline's chief executive Shai Weiss and Britain's Transport Minister Mark Harper among the small number of people on board. 

It was the first transatlantic flight by a large passenger plane powered only by alternative fuels. It was fueled by 100 percent sustainable aviation fuel (SAF) - and aims to show the world the potential of the aviation industry to use low carbon options to reduce emissions and secure its future.

But Cait Hewitt, Policy Director at the Aviation Environment Federation, says the flight is a publicity stunt. "We're calling it a gimmick," she said to CGTN Europe before the flight took off at 11:49 GMT. "It's a gimmick rather than a game changer. There are some alternative fuels that are more sustainable than others. It remains the case that 99.9% of aviation fuel is kerosene. 

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"The flight isn't going to change that fact. It's using fuel made out of waste that is very clearly not going to be possible to scale up sustainably in the future. So I think we need to have a bit more honesty in this debate."

Aviation industry's race to decarbonize

As the world decarbonizes, airlines are banking on fuel made from waste to reduce their emissions by up to 70 percent, enabling them to keep operating before electric and hydrogen-powered air travel becomes a reality in the decades to come.

Aviation accounts for an estimated 3 percent of global carbon emissions. SAF is key toward reducing those emissions, but it is costly, at up to five times as much as regular jet fuel right now, and accounts for less than 0.1 percent of total global jet fuel in use today.

Tuesday's flight, operated by a Virgin Boeing 787 powered by Rolls-Royce Trent 1000 engines, is the first time a commercial airliner has flown long haul on 100 percent SAF. But it is a demonstration flight, with no paying passengers or cargo, and will fly back to Britain using regular jet fuel.

Engines in commercial use are not yet certified to fly on more than 50 percent SAF and the vast majority of flights blend in a much lower amount with traditional jet fuel.  SAF is already used in jet engines as part of a blend with traditional kerosene, but after successful ground tests, Virgin and its partners Rolls-Royce, Boeing, BP and others won permission to fly using only SAF.

Is SAF actually sustainable?

Virgin said the fuel used to power Tuesday's flight was mostly made from used cooking oil and waste animal fat mixed with a small amount of synthetic aromatic kerosene made from waste corn. But Hewitt says there are doubts among environmental experts within the industry over the merits of SAF.

"The other big problem that we don't hear very much about is that when this fuel is burned in an aircraft, this alternative fuel made out of used cooking oil and other waste, it actually emits at the tailpipe as much CO2 as kerosene," she said. "Now, the industry will say that doesn't matter because they've offset those emissions through the process of producing the fuel, using using biomass. We're not so sure about that. 

"So, I think there are some really important conceptual questions still to be asked about whether or not we should be simply ramping up supply of this kind of alternative fuel. We're trying to avoid saying sustainable aviation fuel. We think that's an industry term. But they will tell you all it needs to be done is to produce more of this stuff. We're not so sure that that's the case."

Hewitt says political leaders also need to start being more honest about the challenges facing the industry. "It would be helpful from our political leaders and trying to pretend that the aviation industry is on the verge of decarbonizing and therefore no one needs to worry about the carbon impacts of their flight.

'We should fly less to reduce emissions'

Many European airlines - including Virgin, IAG, and Air France - have said they want to be using 10 percent SAF by 2030, and the industry's goal of "net zero" emissions by 2050 relies on that share rising to 65 percent. 

Rolls-Royce's CEO Tufan Erginbilgic said SAF was the only solution to decarbonize commercial flights in the medium term. He said:"I think on the big planes, the next 15-20 years solution is genuinely SAF. We are making our engines compatible with SAF, so that transformation actually takes place."

But Hewitt has doubts on the ability of the industry to decarbonize at speed. "The climate can't wait for the aviation industry to come up with better solutions than what we've got here today. So we should be talking about new technologies for the future for sure. Zero emission aircraft, carbon capture, that kind of thing. But for now, the best way to cut emissions from aviation is is to fly less."

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