The aviation industry is making significant strides towards sustainability, from new generation aircraft and engines to innovations in packaging and waste management. The International Civil Aviation Organization (ICAO) has committed global commercial aviation to a target of net-zero operations by 2050, and there are several key initiatives underway to help the industry hit this target. One such initiative is the development of Sustainable Aviation Fuel.
What is Sustainable Aviation Fuel?
Sustainable Aviation Fuel, often abbreviated to SAF, is a type of jet fuel produced from renewable and sustainable sources. Unlike conventional fuel derived from fossil fuels, SAF is made from feedstocks such as agricultural residues, waste oils, and biomass. These feedstocks are processed to create a fuel that meets the same rigorous safety and performance standards as traditional jet fuel.
How are Sustainable Aviation Fuels Made?
The production process of SAF involves several steps. First, feedstocks like used cooking oil, algae, or plant waste are collected. These feedstocks are then refined and converted into a fuel that closely mimics the chemical composition of conventional jet fuel. SAF is designed to be a ‘drop-in’ replacement, meaning it can be used in existing aircraft engines without modification.
The most common methods of SAF production are the Fischer-Tropsch process, which converts biomass or natural gas into a liquid fuel, and the hydroprocessing method, which involves treating feedstocks with hydrogen to create aviation-grade fuel. The resulting SAF can have different carbon reduction profiles depending on the feedstock and production method used, with some SAFs achieving substantial emissions reductions.
How is SAF being adapted?
Manufacturers and airlines are working hard to incorporate SAF into their designs and operations, and most new generation engines are capable of operating with a proportion of SAF.
A recent notable example saw an Airbus A321XLR operate with 100% Sustainable Aviation Fuel. As part of the VOLCAN project (VOL avec Carburants Alternatifs Nouveaux, French for “Flight with new alternative fuels”), Airbus’ A321XLR D-AVZO powered by CFM LEAP-1A engines became the first Airbus single aisle aircraft to conduct a test flight on 100% SAF in both engines. The aircraft was accompanied by a specially modified Falcon 20 jet that flew within 100 meters of the A321 to analyze exhaust gasses from the narrowbody.
More recently, Boeing, NASA and United Airlines (UA/UAL) began testing 100% SAF flights using a Boeing 737-10 destined for United, with the first flight commencing in October 2023. Once again the test aircraft was trailed by another, in this instance, NASA’s DC-8 Airborne Science Lab.
There are several key drawbacks of SAF, the biggest of which is supply. The current levels of SAF production are nowhere near high enough to keep up with the increased demand from operators keen to meet increasing targets, and a result, the cost of SAF can be up to four times higher than traditional jet fuels. An increased cost to an airline typically means an increased cost to the customer. Considering SAF forms the backbone of the aviation industry’s plan to reach net-zero emissions by 2050, this divergence in supply and demand will need to be fixed if this target is to be met.
Another issue is that certain SAF feedstocks have a more significant environmental impact than others, and the process of cultivation, harvesting, storage and transportation involved in producing SAF varies between each feedstock. Amongst the most environmentally friendly feedstocks are Hydoprocessed Esters and Fatty Acids (HEFA). These are essentially waste fats, oils and greases. The good thing about these is that the infrastructure is in place to begin producing these at scale. The bad thing is that supply of the HEFAs themselves is limited.
The increased use of biofuels may reduce emissions at the aircraft exhaust, but the agricultural expansion which will be needed globally will likely intensify the CO2 concentration in the atmosphere, and lead to the potential removal of rainforests. Clearly the required ramp up in SAF production will need to be managed carefully and effectively to ensure that scalability can be achieved without detrimental impacts elsewhere.
Whilst there are clearly huge challenges to decarbonizing aviation, it is important to recognize the efforts made so far by operators and manufacturers to kick start the journey to net zero. It is also important to view aviation’s contribution to CO2 emissions in the right context. Aviation is responsible for around 2% of global CO2 emissions annually, 95% of which are from flights over 1,500 nautical miles where no viable alternative exists.
Sustainable Aviation fuel is undoubtedly a vital tool in the arsenal on the aviation industry’s journey to net zero, but other technologies under development, such as hydrogen and electric power sources and carbon capture will also have to play their part. Aviation is an inherently innovative industry, powered by innovative people who are working hard on the solutions we need to reduce the carbon footprint of our industry.
Cover photo: Emmanuel NARGIL, JetPhotos
