In 2019, the last year of typical air travel before COVID throttled the industry, airlines consumed a global total of 96 billion gallons of fuel. Only 0.1% was sustainable aviation fuel (SAF), or fuel made from renewable or waste-derived sources rather than from fossil fuels. That also tracked for United Airlines, the biggest airline in the U.S. by fleet size; that year, of the 4 billion gallons of fuel it burned, only 1 million was SAF.
Yet United Airlines has pledged to be 100% carbon neutral by 2050—and SAF will have to play a large role in achieving that goal. This week, the airline announced its first international SAF venture, the purchase of up to 52.5 million gallons to use toward every flight departing from Amsterdam’s Schiphol Airport over the next three years.
The fuel is from SAF producer Neste, for whom it will be the largest purchase agreement by a passenger airline in history. But United admits it’s not enough to reach its carbon neutral goal, and industry conditions will need to change to increase its ability to use more SAF, including supply, cost, and regulation, much of which it says comes down to legislation.
Manufacturers can produce SAF from feedstocks, such as solid waste, municipal trash, and forestry residue. Since 2007, Finnish company Neste has produced renewable diesel, and has since turned to making SAF out of animal fats and cooking oils, much of which is leftover from fast food fryers (it’s had partnerships with eateries from McDonald’s and Taco Bell to mom and pop shops). It’s currently partnering with United, Alaska, Delta, and JetBlue to run SAF flights out of San Francisco. But for a U.S. airline to go international with SAF was important, says Lauren Riley, United’s chief sustainability officer, “to show that the industry can actually transition flying on SAF on a more regular cadence.”
Though the program may expand to other airports later, it’s initially meant to serve every flight coming out of Amsterdam, no matter the destination. Crucially, SAF infrastructure already exists in the Dutch capital, an important factor for when legacy systems from conventional jet fuel can be hard to work around. The adapted system—which allows for the storage of the fuel at Schiphol—has been in place due to an established SAF partnership with KLM, regularly voted one of the world’s most sustainable airlines.
The flights will contain a blend of 25% to 40% SAF, topped up with conventional fuel. Passenger flights cannot legally fly with more than 50% SAF, according to regulations by world standards organization ASTM. “That ceiling of 50% today is arbitrary,” Riley says. “The SAF that we use today is a lot more sophisticated, and it works exactly like conventional jet fuel.” To prove that planes can fly safely with 100% SAF, United undertook the first 100% SAF test flight from Chicago to Washington,D.C., approved by the FAA, last December. Chris Cooper, Neste’s vice president of renewable aviation in North America, explains that it seems arbitrary to a company like United, whose fleet is relatively modern, but that older engines need to be safety certified, too. “It’s really just a number that will eventually become 100%,” he says.
Still, a lack of supply means reaching that percentage goal is far off. “There’s simply not enough out there,” Riley says. “There’s no way we’re gonna get near 50% on some of our flights.” Since 2016, United has also partnered with SAF producer World Energy, for flights from LAX; it’s also invested in newer startups like Fulcrom Biomass, which makes its SAF from household garbage, and Alder Fuel, from which it will buy 1.5 billion gallons of its biomass-derived fuel.
SAF is also costly, at four to five times more than regular jet fuel. Riley assures that increases won’t be felt by the regular flyer. “This is United’s purchase,” she says. “There will not be a flow-through financial impact on any of our customers.” It will get some help via its Eco Skies Alliance, whereby corporate customers, keen to meet their own organizations’ climate goals, volunteer to pay the actual premium price for SAF. Last year, the alliance financed more than 7 million gallons of fuel, and the program will launch again this year.
Both United and Neste say that federal legislation would help increase supply and lower costs. They advocate for the passing of the Sustainable Skies Act, a proposed bill introduced in the House by Illinois Democrat Bradley Schneider that would allow a Blended Tax Credit, a tax credit for SAF production, similar to those received by producers of renewable diesel, for fueling ground transport like buses and trucks. The same companies often make both—Neste is also the biggest producer of renewable diesel in the world—and for them, Riley says, the credit “really provides an incentive to want to produce sustainable aviation fuel at parity to renewable diesel.” Most recently, the bill was included in the Democrats’ Build Back Better legislation, which has yet to pass in the Senate.
United hopes this passage would help it meet its own goal, to reach net zero emissions by 2050—without the use of carbon offsets. That’s partly to push back on criticisms. “For us, it’s a little disingenuous to claim success by purchasing carbon offsets,” Riley says. “It’s important to us to point that out because there’s a lot of scrutiny of, are we serious? Are we really committed to change, and are we willing to fund it?”
United has also committed to funding other nascent technologies like hydrogen-electric engine development, and another that would suck carbon directly out of the atmosphere. But with those promises comes the pledge that it will keep the same number of its planes in the sky (the company already boasts the most destinations of any U.S. carrier, and this year increased its long-haul routes). It’s also investing in supersonic jets that can zip from New York City to London in 3.5 hours, and L.A. to Sydney in 8.5—and which use 5 to 7 times more fuel. United says it will be using 100% sustainable fuel by its first supersonic flight in 2029.
That’s a different roadmap from other airlines, like KLM, which actually ran a campaign encouraging customers to decrease their flying habits. “I think the world would get too small if that happens,” Riley says. “So really, the question isn’t to fly or not to fly. It’s how do we fly sustainably?”