With the worst of the pandemic downturn hopefully in the rearview mirror, commercial aviation must now move on to face its greatest challenge yet: How to achieve net-zero emissions by 2050. Governments are making commitments to incentivize sustainable aviation fuel (SAF)-Europe, through February's "Toulouse Declaration," and the U.S., with the Biden administration's aim to have enough SAF to meet 5-10% of jet fuel demand by 2030 and 100% by 2050, including through tax credits. A growing list of nations, industry associations, airlines and manufacturers have voiced their intentions, positioning SAF to play a key role in achieving net zero. Although still in its infancy for adoption, SAF has generated excitement as an attractive "bridge" to future technologies that may eventually include zero-emission aircraft. While SAF produces carbon emissions, many feedstocks are considered largely carbon-neutral as they "catch and release" already emitted CO_2. eFuels are especially promising, given their potential to reduce life-cycle emissions by 90% compared with Jet A when combined with renewable sources of electricity and CO_2. As a drop-in fuel, SAF is mostly compatible with today's engines and does not require costly fleet replacements. And unlike other propulsion technologies-such as electricity and hydrogen, which will be limited to short- and medium-haul missions, given energy and volumetric density limitations-SAF offers a ubiquitous option. Several pathways are already approved at blends of up to 50%, with the feasibility of 100% SAF flights already demonstrated, including a passenger-carrying United Airlines Boeing 737 MAX. Thus, many commitments have been made by public and private stakeholders to produce and purchase SAF.
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