United Airlines flew more than 100 passengers on a new Boeing 737 MAX 8 from Chicago’s O’Hare International Airport to Reagan National Airport in Washington, D.C. on Wednesday. The 612-mile trip used “sustainable aviation fuel” (SAF) on an unprecedented scale for a flight with many people on it.
Airlines are currently eligible for a $1 per gallon tax credit for using biodiesel fuels. Although this subsidy is slated to expire in 2022, the House version of the Build Back Better Act that passed Nov. 19 includes a new biodiesel tax credit specifically designed for aviation with a floor of $1.25 per gallon, along with “the applicable supplementary amount with respect to such sustainable aviation fuel.”
United’s press release on the flight was titled “United to Become First in Aviation History to Fly Aircraft Full of Passengers Using 100% Sustainable Fuel.” That press release noted that just one of the plane’s engines used 100 percent SAF in its 500-gallon tank, while the other used conventional fuel.
United’s press release also stated the fuel was “drop-in ready,” meaning it can be used with the same infrastructure, such as pipelines, and in the same engines as conventional petroleum fuels.
“This flight is historic because we secured permission to operate one engine on 100% SAF with the other running on conventional jet fuel to prove there are no operational differences between the two—and to set the stage for the future of aviation with more scalable uses of SAF,” United wrote in a tweet on the flight.
In that same thread, United said its flight generated 75 percent less carbon dioxide than an equivalent flight relying on conventional jet fuel alone.
The airline uses SAF from Boston-based fuel supplier World Energy. United had earlier agreed to purchase “up to 10 million gallons of cost-competitive, commercial-scale” SAF from World Energy for two years beginning in 2020.
The plane’s use of 100 percent SAF for an engine was enabled by synthesized aromatic kerosene (SAK) technology from Virent, a Marathon subsidiary.
An October press release from Virent described a United Airlines test flight without passengers that used the company’s SAK, which it said was produced using sugar from Iowa corn.
“For this flight, Virent used corn sugar to manufacture the fuel component that made petroleum blending unnecessary, and so yesterday’s flight demonstrates that we can power sustainable aviation without modifying today’s modern airline engines or the infrastructure that serves the airline industry,” said Virent president and general counsel Dave Kettner in a press release on the Wednesday flight.
Richard Schuurman of AirInsight pointed out that the Wednesday flight was an experimental one, not a regular commercial run.
“The message is that United Airlines, Boeing, CFM, World Energy, and Virent all want to push for 100 percent SAF in their quest to reduce the carbon footprint of aviation,” Schuurman wrote.
United told BusinessGreen that the SAF on its Chicago-to-D.C. flight was one-fifth Virent SAK and four-fifths hydro-processed esters and fatty acids (HEFAs).
A 2020 report from Biofuelwatch claimed that World Energy relied on corn oil, tallow, and used cooking oil/yellow grease as feedstocks for its SAFs.
In that report, Biofuelwatch criticized World Energy for what it described as the “greenwashing of airlines and airports.”
Some climate scientists have identified air travel as a major source of carbon emissions, spurring proposals that claim it must be sharply curtailed in the future.
The “Absolute Zero” report, produced with British government support by the U.K. FIRES research consortium, argues that greenhouse gas emissions must be cut “to zero by 2050.” The report says aviation must be made illegal to accomplish this.
United CEO Scott Kirby, who took part in the Chicago-to-D.C. flight, described it as “a significant milestone for efforts to decarbonize our industry.”
The U.S. Department of Energy (DoE) credited its Bioenergy Technologies Office (BETO) with nurturing some of the research that enabled the United flight.
“The goal is to have such fuels meet 100% of aviation fuel demand by 2050,” wrote the DoE’s Scott Minos in a blog post on the flight.