If there were naysayers sounding off when KLM Royal Dutch carried 70 passengers from Amsterdam to Paris in July in a plane powered by a 50-50 mix of biofuel and conventional fuel, we didn’t hear them. Likewise when Finnair used biofuel for a commercial flight from Helsinki to Amsterdam. Thomson Airways, however, was not so fortunate for its maiden biofuel flight, from Birmingham, England, to Arrecife, in the Canary Islands.

As soon as Thomson announced its intention to make the flight – the first commercial flight from the U.K. using biofuel – Friends of the Earth was out with a press release denouncing the plan. “Biofuels won’t make flying any greener – their production is wrecking rainforests, pushing up food prices and causing yet more climate-changing emissions,” the organization’s Kenneth Richter said in a statement. In addition, the groups Biofuelswatch and AirportWatch put out a joint statement calling the Thomson flight “dangerous greenwash.” And here Thomson thought it was doing a good deed.

image via Thomson

“We firmly believe the adoption of sustainable biofuels by airlines will help achieve the government’s carbon budget which commits the U.K. to reduce its carbon emissions by 50 percent by 2025,” Managing Director Chris Browne said. “Most strikingly, sustainable biofuel has the potential to reduce aviation emissions by up to 80 percent in the long term.”

The fuel that Thomson used – the flight went on as planned – was supplied by SkyNRG, which also supplied KLM and Finnair for their flights. While Friends of the Earth’s claims might indeed have validity for some biofuels, SkyNRG’s product for those demonstration flights was produced by Dynamic Fuels, a partnership between the synthetic fuel manufacturer Syntroleum and the meat production giant Tyson Foods. Together, the companies established a venture that has been converting fats, oils and greases into fuels at a plant in Geismar, La., just south of Baton Rouge, since late last year. It’s not precisely clear if Thomson’s fuel came from the same producer, but the airline said emphatically: “The biofuel purchased by Thomson Airways is sourced entirely from used cooking oil.”

So this biofuel apparently has the virtue of not being made directly from food crops. Whether that will be the case in the future is less certain, however. SkyNRG has said [PDF] that it “does not commit to one single feedstock or technology,” and that “the sustainability of alternative aviation fuels depends on many factors and has to be assessed on a case-by-case basis.”