The Near-Term Solution for Aviation Sustainability: Sustainable Aviation Fuel (SAF)

Since low-carbon technologies, such as electric and hydrogen propulsion, are unlikely until 2040 and beyond, the use of sustainable aviation fuel (SAF) is on the rise as a viable, carbon-reducing bridge to a future of hybrid and all-electric aircraft. SAF, which is made from renewable biomass and waste feedstocks, is promising for reducing carbon emissions because it offers similar performance to traditional jet fossil fuels, yet it has a significantly smaller carbon footprint. Multiple blends of SAF have been approved by industry standards developer American Society for Testing and Materials (ASTM) International; however, the majority of SAF produced today is a synthetic kerosene called HEFA (hydro processed esters and fatty acids), made from energy-dense animal fats and vegetable oils, such as used cooking oil.

While production costs remain high for SAF as an emerging technology, the decision was made early on to keep SAF technically simple as a drop-in fuel that can replace traditional jet fuel without any modifications to aircraft or engines. The drop-in rate for SAF is currently limited up to 50%, due to HEFA limitations required for chemical compatibility with fuel seals. However, some companies are increasing targets for 100% SAF, blending different chemical components to make aircraft engines completely compliant with SAF.  

SAF provides a significant environmental impact, reducing carbon emissions up to 80% when compared to traditional jet fuel, depending on feedstock used and other factors. Since the current 50% fuel blend limitation also reduces maximum achievable carbon reduction, efforts are underway to scale up aircraft compatibility and overall SAF production. To note, SAF doesn’t substantially reduce in-flight combustion emissions as compared to fossil fuels; however, SAF does have significant advantages for carbon emissions over the life cycle of the fuel. For example, conventional fuel starts as crude oil in the ground that must be extracted and pumped or shipped to a refinery and then shipped again to an airport where it goes into an aircraft to be burned in an engine. The SAF process includes growing, transporting, and refining bio-based feedstock (CO2 is absorbed by plants during the growth of the biomass, essentially canceling out the emissions from combustion), or for animal fats, the life cycle involves growing food for livestock, processing the animals, and then converting the animal fat in a refinery. If cheaper ingredients, such as palm oil or other crop-based additives, are substituted in the process, then deforestation must be considered.

To further evaluate this fuel technology, the ultimate hurdle in aviation—safety—has been met, as flying with 100% SAF is not new. In 2012, Canada’s National Research Council conducted its first flight on 100% biofuel. Since then, according to the International Air Transport Association (IATA), SAF has fueled over 350,000 flights around the world, and more than 45 airlines now have experience with SAF. In December 2021, United Airlines made history by operating the world’s first passenger flight on 100% drop-in SAF produced by low-carbon fuel maker, World Energy. A new United Boeing 737 Max 8 with GE engines made the flight from Chicago’s O’Hare International Airport to Washington’s Reagan National Airport with one engine using 100% SAF and the other engine burning conventional jet fuel. The “drop-in” achievement demonstrated that the fuels used in each engine were identical in composition and can be used without any modification to the engines or the aircraft’s internal fuel system. 

Despite its potential for reducing CO2 emissions, SAF is currently three to five times more expensive than fossil jet fuel and represents less than 0.1% of global aviation fuel. There are also issues with potential limited supply of sustainable feedstock, and SAF refineries are not currently operating at commercial scale. However, costs are coming down as SAF production increases, alliances are formed to encourage greater demand, and government programs and incentives are introduced.

In July 2021, as part of the European Green Deal, the EU announced a wide set of proposals aimed at decarbonizing the aviation sector. In this announcement, the ReFuelEU Aviation Initiative ordered the mandatory blending of SAF with fossil fuels: 5% by 2030, 32% by 2040, and 63% by 2050. At the COP26 conference in Glasgow in November 2021, the Sustainable Aviation Buyer’s Alliance (SABA) announced the creation of an Aviator’s Group, including Amazon Air, Alaska Airlines, JetBlue, and United Airlines to promote investment in SAF and increase its usage. The Aviator’s Group joined founding SABA companies, Boeing, Bank of America, Boston Consulting Group, Deloitte, JP Morgan Chase, McKinsey, Meta, Microsoft, Netflix, and Salesforce, along with collaborators Environmental Defense Fund and Rocky Mountain Institute, to accelerate the use and drive down the costs of SAF—with a goal of meeting science-based reduction targets for aviation emissions. The airlines are also making climate commitments with SAF. Delta Airlines has pledged to replace 10% of its jet fuel use with SAF by 2030, signing agreements with SAF producers Neste, Gevo, and Northwest Advanced Bio-Fuels. In September 2021, JetBlue announced plans to speed up its transition to SAF with an offtake agreement with SG Preston, contributing to its target to convert 10% of its fuel to SAF on a blended basis by 2030.

Finally, the aviation industry contributes to 2.5% of global carbon emissions each year. In October 2021, the IATA announced a timeline for getting to net-zero emissions by 2050, and two-thirds of the roadmap relies on SAF. For SAF to scale, new or substantially improved technologies for processing and refining SAF will need to be introduced. The promotion of industry alliances, paired with tax credits, favorable loans, and other financial incentives will also be critical to increasing demand for SAF, while driving costs down. The high-cost, low-supply hurdle will have to be comprehensively addressed for the aviation industry to fully embrace SAF as a near-term or long-term solution for reducing aviation-related carbon emissions.