Sustainable Aviation Fuel - An Introduction
What is Sustainable Aviation Fuel?
Sustainable Aviation Fuel (SAF) is a “drop-in” fuel that meets all the same technical and safety requirements as fossil-based jet fuel. SAF contains the same hydrocarbons (and thus the same tailpipe emissions) as fossil-based kerosene, but the difference is that the hydrocarbons came from a more sustainable source. This results in a net reduction of emissions when comparing to fossil jet fuel on a life cycle basis.
Rather than removing carbon from the ground through the extraction of fossil fuels, the hydrocarbons are sourced from sustainable feedstocks like used or waste cooking oils, tallow (waste animal fats), waste biomass, and municipal solid waste (MSW), among others. Additional sustainability criteria are being considered, but today CORSIA requires feedstocks to meet two sustainability criteria in order to qualify as SAF:
1. Achieve at least a 10% net greenhouse gas emissions reduction compared to the baseline life cycle emissions values.
2. Not be made from biomass sourced from land with a high carbon stock.
In addition, SAF cannot be made from edible feedstock sources that directly compete with food production or grown from land that could be used for food production. SAF is refined from these sustainable feedstocks and then certified under ASTM D7566 – a standard for the creation of synthetic fuels. From there, it is blended in approved ratios with fossil jet fuel and certified under ASTM D1655 – the same standard for conventional kerosene. At this point, it can be delivered as a drop-in product to existing fuel farms and airplane wings. SAF still has to be blended today due to the lack of aromatics in the fuel which are often needed in aircraft engine fuel systems. However, engines, including ones for business aviation, are being developed today to burn 100% SAF.
How are emissions reductions realized?
A common misconception is that SAF reduces physical “tailpipe” emissions. While some emissions of sulfur oxides (SOx), particulate matter (PM), and potentially nitrogen oxides (NOx), may be reduced depending on the feedstock, the CO2 emissions are the same between SAF and fossil jet fuel. The emissions reductions from SAF are realized when comparing the life cycle emissions of: 1) the source of the hydrocarbons and 2) the effects of '“induced land use change” (ILUC). ICAO defines land use change as:
“CORSIA Eligible Fuel production may require some additional land to be used, and generate land use change GHG emissions. These could occur where the new CORSIA Eligible Fuel production is taking place (direct land use change) but also in other locations due to the displacement of crops (or animals) for which the land was previously used (indirect land use change). ILUC emissions assessment accounts for these different effects, by evaluating greenhouse gas released from conversion of natural vegetation (forest, other natural land), soil organic carbon, oxidation of peatlands, and sequestered biomass.”
CORSIA provides default life cycle emission values for approved fuels that incorporate the carbon intensity of the feedstock as well as the land use change effects compared to the fossil jet fuel baseline. These values are compared to the CORSIA baseline of 89gCO2/MJ for fossil jet fuel to calculate a percentage reduction. This percentage reduction can be multiplied against the carbon intensity (3.16kgCO2/kgJetA) of jet fuel to calculate the net emission reductions.
Where should I start?
Consider looking at converting a fraction of your annual fuel consumption to SAF as part of your climate strategy. Even just 1-5% can provide meaningful volumes and help mobilize additional SAF supply while decreasing the premium above jet fuel. Spreading out the incremental cost for a small portion of SAF across an entire fuel budget minimizes any budget impact.
Talk to your FBO or fuel supplier to ask if they have SAF or consider visiting airports with supply. In order to maximize the sustainability impact, avoid trucking the fuel long distances or tankering large volumes.
Feel free to contact us as well, 4AIR is happy to answer any questions around SAF or assist with understanding your options in supporting the fuel.
FAQ –
Is it safe? Once blended, SAF is certified under ATSM D1655, the same standard as conventional jet fuel, meaning it has the same technical and safety characteristics as conventional fuel. Therefore, no modifications are needed for use in existing pipelines, fuel farms, trucks, tanks, or engines.
Why is it blended? Depending on the feedstock, not all SAF contains the same aromatics as fossil jet fuel, which are sometimes needed in aircraft fuel systems. Each feedstock has a maximum blend depending on this and in general, to be conservative, the highest allowable blend for any SAF is 50% - though most commercially-available blends will only be 30-38%. Engines are being tested on 100% unblended SAF, including engines for business jets. The expectation is that 100% SAF will be certified for use in aircraft in the near future.
Does SAF reduce my direct emissions? SAF is one of the most practical and readily available opportunities for aviation to reduce its in-sector footprint, however the reductions do not come from a reduction of physical tailpipe emissions. Rather, by comparing the greenhouse gas emissions of the SAF to fossil jet fuel across the entire life cycle, SAF is able to deliver net GHG reductions up to 80 to 90% compared to fossil jet fuel. There are some pathways being explored that would enable reductions greater than 100%, effectively providing a net sequestration of carbon during the life cycle of the fuel.
If I visit an airport that already mixes in SAF, why do I need to pay for it? Due to its drop-in nature, most SAF is mixed into existing airport fuel farms so all aircraft visiting may receive a small portion when fueling at these locations. However today, in order to be able to claim the emissions reductions from the use of the fuel, you must actually purchase the SAF and receive documentation affirming your quantity received. Without this, there is no right to claim any reductions from the use.
Where can I find it? 4AIR announced a new interactive map to assist aviation stakeholders in finding airports with verified, physical SAF inventory. Emerging book and claim programs will expand the geographical availability of SAF, but until then, this resource can be used to find airports with supply.
Additional Resources
ICAO – An Overview of CORSIA Eligible Fuels (CEF)
Business Aviation Coalition for Sustainable Aviation Fuel – Sustainable Aviation Fuel Guide
ATAG – A Beginner’s Guide to SAF
Still have questions about SAF? We can help. Complete the form below, and a 4AIR representative will contact you to answer questions or walk you through our SAF Inventory Management Program.