Sustainable Aviation Fuel Assumptions

There are multiple meanings of the term “SAF,” or sustainable aviation fuel. Specific U.S. and international definitions are provided here because commercial aviation is a global business. We also identify the role of biomass sources and greenhouse gas (GHG) reduction targets in the SAF definition, including the additional criteria that must be met to make the U.S. definition consistent with the international definition.

For the United States, the U.S. Department of Energy used the following definition in SAF Grand Challenge: “SAF is drop-in liquid hydrocarbon jet fuel produced from renewable or waste resources that is compatible with existing aircraft and engines” (U.S. DOE, 2022). Although some may consider SAF to refer to pathways derived only from oils, in this definition, SAF refers to drop-in hydrocarbon jet fuel from a variety of pathways. Despite this definition, there are pathway-dependent blend ratios, and a 50% by volume maximum, that limit the amount of SAF that may be mixed into jet fuel.

Further defining SAF in a U.S. context, the Commercial Aviation Alternative Fuels Initiative (CAAFI) defines SAF as Jet A fuel blendstock that:

1. Reduces net life cycle CO₂ emissions from aviation operations
2. Enhances the sustainability of aviation by being superior to petroleum-based jet fuel in economic, social, and environmental aspects
3. Enables drop-in jet fuel production from multiple feedstocks and conversion processes, so no changes are required in aircraft or engine fuel systems, distribution infrastructure, or storage facilities. As such, SAF can be mixed interchangeably (is fungible) with existing jet fuel. (Quoted from CAAFI Frequently Asked Questions.)

Internationally, the International Civil Aviation Organization (ICAO) establishes criteria for eligibility for credits under the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA): 

Greenhouse Gas Criterion 1: CORSIA eligible fuel shall achieve net GHG emissions reductions of at least 10% compared to the baseline life cycle emissions values for aviation fuel on a life cycle basis.

Carbon Stock Criterion 1: CORSIA eligible fuel shall not be made from biomass obtained from land converted after January 1, 2008, that was primary forest, wetlands, or peat lands and/or contributes to degradation of the carbon stock in primary forests, wetlands, or peat lands because these lands all have high carbon stocks. 

Carbon Stock Criterion 2: In the event of land use conversion after January 1, 2008, as defined based on IPCC [Intergovernmental Panel on Climate Change] land categories, direct land use change (DLUC) emissions shall be calculated. If DLUC GHG emissions exceed the default induced land use change (ILUC) value, the DLUC value shall replace the default ILUC value. (Quoted from (ICAO, 2019).)

The SAF pathways presented in the Annual Technology Baseline (ATB) could meet the CAAFI definition as well as the ICAO CORSIA greenhouse gas criterion of 10% GHG reduction, depending on their actual life cycle emissions. (The CAAFI definition does not state a specific target for GHG reduction relative to Jet A.) The SAF Grand Challenge targets a GHG reduction of 50% relative to Jet A, which is a greater reduction than SAF as defined here. If biofuels in the United States will be derived from biomass resources identified in the 2016 Billion-Ton Report (U.S. DOE, 2016), this would not include resources from old-growth forestland, consistent with part of ICAO CORSIA carbon stock eligibility criterion 1. If the other ICAO criteria are satisfied, the SAF pathways shown in the ATB would be compliant both domestically and globally.

References

The following references are specific to this page; for all references in this ATB, see References.