Full Circle Moment
The 2009 IATA Biofuels commitment turned out to be a full circle moment. The commitment did not introduce legally binding quotas on members, but instead made a landmark industrywide commitment to pursue sustainable aviation fuels as a core strategy for decarbonization. This included a pledge to achieve carbon-neutral growth from 2020 onwards (no increase in carbon dioxide emissions from a 2005 baseline) and to cut net carbon emissions in half by 2050 compared once again to a 2005 baseline.(73rd IATA Annual Meeting 2010)
The pledge kickstarted global SAF adoption and over 400,000 commercial flights have used SAF since then (World Economic Forum 2022/ GE Aerospace 2022). The 2009 commitment led to 2021’s ‘Fly Net Zero’ initiative, targeting net-zero emissions by 2050.
This piece looks at not just biofuels but other options as well.
The Background
Aviation Turbine Fuel (ATF) has the following strengths. The first is the ability to operate at low ambient temperatures,the second is to have a high calorific value, this is measured by the heat produced by a specific quantity, measured as J/kg (1 Wh/kg = 3600 J/kg). The third is volumetric energy density that is the amount of energy that can be stored within a given volume and is measured as Wh/L and ATF with a volumetric energy density of 35 MJ/L has high density. A flashpoint of 49 degrees centigrade obviously makes it combustible and needs to have safety protocols while being handled. Lastly ATF is cheap to manufacture at approx $1.0 per liter. (Aviation Fuel Wikipedia)
By the mid 2000s aviation was under intense scrutiny for its contribution to global greenhouse gas (GHG) emissions. Aviation was responsible for approx 2-3% of all carbon dioxide emissions, and was projected to grow rapidly. (expected to be over 25% by 2050).
While other forms of transport (road,rail,sea) had multiple forms of green propulsion coming up mainly dominated by electricity. Aviation had yet to see any move in the direction of decarbonizing. While the 2009 Copenhagen Climate Conference emphasized sector specific emission reductions there were other contributory incidents as well.
The 2008 financial crisis led to oil spiking at $147/barrel in July of that year and this only drove the point home to airlines, the need to hedge against fossil fuels. Biofuels did offer a hedge against this dependence, potentially stabilizing costs, Giovanni Bisignani of IATA emphasized that fuel innovation was key or else fuel would account for over 40% of airline costs by 2020 ( Reuters Factbox 2008, multiple sources)
By 2009, airframe and engine manufacturers had validated biofuels performance & safety and Virgin Atlantic flew the first flight with a SAF blend in 2008. Furthermore biofuels did not require any aircraft or engine modifications unlike electricity or hydrogen.
Growing calls from countries & private bodies like ICAO further influenced IATA to work on emissions reductions. Aviation was included by the EU in its emission trading system (ETS, a cap and trade policy that sets a cap on the total GHG emissions from specific industries) and added financial incentives/penalties for decarbonization. The commitment preempted stricter regulations through self regulation and fostered collaborations like the Sustainable Aviation Fuel Users Group that was launched in 2008 and united producers, airlines & NGOs to ensure biofuels met sustainability criteria.
SAF
The roots of the idea of SAF can be traced back to the mid 20th Century with the 1940s Fischer-Tropsch (FT) Synthesis. The process which has its roots back in the 1920s was developed by German scientists Franz Fischer and Hans Tropsch to convert coal or biomass into liquid hydrocarbons, including kerosene like fuels (ATF is kerosene). While originally developed to overcome wartime shortages, FT synthesis laid the foundational work of producing jet fuel from non fossil sources.
The Oil shocks of the 1970s further spurred global interest in developing alternative fuels. In 1974 Brazil started the ProAlcool program which produced bioethanol from sugarcane for road transport vehicles. This program demonstrated the scalability of biofuels and catalysed interest in bio-jet fuels.
The 1997 Kyoto Protocol further heightened global focus on GHG emissions. Aviation, which then contributed about 2% of global carbon dioxide emissions, was growing rapidly with no alternatives to ATF came under scrutiny. Initial studies focussed on adapting ethanol and biodiesel processes, but jet fuel’s need for high calorific values at low ambient temperatures shifted focus to hydrotreating (process of removing impurities such as sulphur and improving fuel quality) & FT synthesis.
Recognizing that biofuels were the path to decarbonizing, with minimal changes to aircraft & infrastructure, the concept of drop-in fuels gained traction. The SAF concept crystallized in 2005 as the quickest solution and was adopted by IATA in 2009 using 2005 as a baseline.DARPA (Defense Advanced Research Projects Agency) took specific interest in this project.
The newfound synergy between all the stakeholders resulted in the first tangible steps. Honeywell UOP partnered with DARPA to develop the renewable jet fuel process. Boeing collaborated with airlines, fuel producers & research facilities to further explore the practical application of bio jet-fuel.
SAF is produced through multiple refining processes that convert feedstocks into drop-in fuels. These processes or pathways convert diverse raw materials such as waste oils, biomass or captured carbon dioxide into hydrocarbons that mimic fossil based jet fuel while reducing lifecycle GHG emissions by 80%.
HEFA (Hydrotreated Esters & Fatty Acids) uses feedstocks of waste cooking oils & animal fats removes oxygen from triglycerides & fatty acids ( fat the human body stores, remember this is from cooking oil)producing paraffinic hydrocarbons (linked carbon and hydrogen atoms, found in fuels and known for their clean burning, high energy density properties)via hydrogenation.Simply put it is gather the grease, remove the oxygen, make fuel like molecules by adjusting the molecular chains or makes fuel from unwanted oils. This process produces top quality SAF. HEFA competes with bio diesel and has limited feedstock availability. However this is still the dominant process and accounts for 80% of all current SAF production. (companies : Neste)
The FT Synthesis uses biomass such as agricultural & municipal waste as feedstock. The biomass is gasified into syngas (carbon monoxide & hydrogen), then catalytically converted into liquid hydrocarbons, which are then refined into jet fuel. While feedstocks are flexible which translates to potentially high volumes, the high capital costs & energy intensive nature of gasification plants are obstacles to the adoption. While certified in 2009, the FT synthesis process is still niche.
Synthesized iso-Paraffins (SIP) / Direct Sugar to Hydrocarbon (DSHC) uses sugars such as sugarcane or corn syrup as feedstock. Fermentation converts sugars into farnesane, a hydrocarbon, which is then hydroprocessed into jet fuel. While this process produces high density fuel, it is a niche pathway with a limited blend ratio and is expensive to produce. (companies: Amyris)
Alcohol to Jet (ATJ) uses ethanol or isobutanol from biomass as feedstock. Alcohols are dehydrated (water is removed), oligomerized (smaller molecules for more efficient & cleaner burning) & hydroprocessed (refined using hydrogen under heat and pressure)to form jet fuel hydrocarbons. Certified in 2016 this process leverages existing ethanol infrastructure and uses versatile feedstocks, however this process is complex and multi-layered, leading to higher costs. (companies: Gevo, LanzaTech)
Power to Liquid (PtL) / Synthetic Fuels (e-SAF) uses carbon dioxide captured from the air directly and green hydrogen (from electrolysis using renewable energy) as feedstock. The carbon & hydrogen are combined using FT or methanol synthesis to produce synthetic hydrocarbons which are refined into jetfuel.While this is still an emerging process, it is an extremely niche method & energy intensive,it is reliant on cheap renewable electricity. The RefuelEU is an aviation initiative that requires 1.2% e-SAF by 2030.
There are multiple other emerging pathways such as Hydroprocessed Hydrocarbons (HH-SPK) that use algae oils, this is not scaled as it damages ecosystems. Catalytic Hydrothermolysis (CHJ) that converts oils/fats under high pressure & temperature. Lignocellulosic (plant biomass) pyrolysis is the fast pyrolysis (decomposition through high temperatures) into bio-oil, this is an experimental process that upgrades bio-oil to jet fuel.
HEFA dominates at the moment because of its maturity & cost effectiveness, but PtL & ATJ are growing fast. Current global SAF production is at 2.5 bn liters/year ( IATA , Jun 2025 press release )of the total global ATF requirement of 300 bn liters/year.
Neste is the world’s leading SAF producer with operations in 14 countries. Its strategy is centered around HEFA technology using its patented NEXBTL technology to produce high quality SAF. It has the early mover advantage and has been helped by EU policy ensuring a ready market for its SAF. Neste prioritizes 100% waste and residue materials such as cooking oil and animal fat waste. It avoids food competing crops such as palm oil (phased out in 2020). Neste produces 25% of global SAF with three refineries, supplies over 20 airlines and airports and uses logistics partner skyNRG for blending & distribution.
SAF continues to face challenges such as limited waste oil supply, and it costs between 2-3x(World Economic Forum, “The cost of sustainable aviation fuel: Can the industry clear this key hurdle?” July 2025). that what ATF costs, however global policy shifts ensure this fuel is the quickest off the blocks in the decarbonization race.
Note: Could not avoid the chemical terms, have tried to explain them succinctly
Hydrogen
Hydrogen has always featured in aviation almost from the beginning. Starting with the early 20th Century when it was used for buoyancy on early airships such as the Zeppelin LZ1 as far back as 1900. Hydrogen is known for its high energy density by weight and is seen as a potential fuel due to its zero carbon emissions.
During the 1930s German engineers conducted turbojet experiments using gaseous hydrogen laying the groundwork for cryogenic (hydrogen needs to be stored at -252.8 degrees C for storage efficiency and maximize payload and range. Cryogenic LH2 tanks, though insulated and complex, enable aircraft to carry sufficient fuel for long flights). Gaseous hydrogen would require impractically large tanks, reducing payload or making the aircraft design unfeasible. This was followed by Sikorsky Aircraft proposing liquid hydrogen as a fuel. By the 1950s liquid hydrogen production was scaled for rocket applications. The USAF’s ‘Project Bee’ began with a Martin B-57B Canberra bomber becoming the World’s first airplane powered by liquid hydrogen. Skunk Works led by Kelly Johnson developed the CL-400 Suntan as a reconnaissance aircraft that ran on P&W’s model 304 hydrogen engines. The project itself was cancelled but advanced liquid hydrogen’s production & tankage for the space program.
Between the 1960s-80s both the US & Soviet Union ran tests on passenger airliners using liquid hydrogen as propulsion. Lockheed looked at 130-140 passenger transports with ranges between 2700 – 9300km and the Soviet Union used a Tu-155 with a Hydrogen fueled engine. Both the programs highlighted storage and boil off challenges.
By the 1980s aerospace research considered hydrogen a clean and promising fuel for long range aircraft because of its high energy content and low emissions. Messerschmitt Bölkow Blohm (MBB) , the company that included the historic Messerschmitt Aircraft Company, was heavily involved in hydrogen research. The company was acquired by Deutsche Aerospace AG (DASA) which in turn would be acquired by Airbus. In November 1989 a major European Colloquium was held in Strasbourg, Germany. The main topic of the Colloquium was the future of supersonic & hypersonic transportation systems, here a paper on hydrogen as a propellant was presented. While MBB was a major player in the hydrogen space in Europe, there were others as well.
By the late 1990s the Hydrogen Cell Era had begun and between 2000-2002 the Airbus led the Cryoplane study which was funded by the European Commission had assessed liquid hydrogen configurations for biz jets and widebody airliners, it emphasized safety and infrastructure transitions.
In April 2008 Boeing’s fuel cell demonstrator , a modified Diamond DA20 eclipse became the first manned aircraft to fly solely on a hydrogen fuel cell (HFC). It was powered by Intelligent Energy’s 24 kW Proton Exchange membrane (PEM) system (the PEM is key to splitting hydrogen molecules, the electrons are stripped and forced into the electrical circuit generating electricity, while protons head to the cathodes) reaching 1,000 meters altitude at 100 km/h for 20 minutes.
Over the next decade multiple organizations such as The German Aerospace Centre, Boeing, AeroVironment etc would make advances in the field of hydrogen flight endurance, altitude,storage pressure (hydrogen being gaseous needs to be cooled and stored cryogenically to maximize fuel), fuel cell architecture. These advances set the ground for the next decade.
The decade of the 2020s has seen increased activity with Airbus announcing its ZEROe project with four hydrogen (combustion & fuel cell) concepts targeting the aircraft in the 100-200 passenger range. While most of the aircraft are conventional there is a Blended Wing Body being tested as well. Airbus targets 2035 for its first first craft with zero emissions.
ZeroAvia is a British/American Hydrogen aircraft developer. In 2020 they tested a hydrogen powertrain on a retrofitted Piper M-class and completed their first eight minute flight. The testbed crashed in 2021 at Cranfield during a power system test, nobody was hurt.Since then ZeroAvia has procured two Dornier 228 . One flew in 2023 for ten minutes with one of its engines powered by hydrogen electricity. ZeroAvia has partnered with Textron Aviation, the parent of Cessna, to develop a hydrogen powered Cessna Grand Caravan.
Universal Hydrogen is yet another company in the field, converting an ATR72-500 & Bombardier Dash 8-300 to hydrogen using hydrogen conversion kits to be retrofitted to flying aircraft. There are multiple other companies in the field focusing on different types of aircraft.
Over the next 25 years expect to see the commercial viability & scalability of hydrogen fuel established in multiple aircraft segments. Airbus definitely heads the area, but there are developments happening across multiple companies and aircraft types. What is critical are the proving flights of today.
Electric
The biggest challenge that electric aircraft face is their energy density. Current lithium-ion batteries have an energy density of 250 Wh/kg which is below ATFs 12,000 Wh/kg. This clearly limits range (once again range anxiety), furthermore batteries add significant weight while reducing payload capacity. Nonetheless, short taxi services are still very much in the picture.
Joby Aviation plans to launch commercial taxi services in Dubai & Los Angeles. They plan to have electric vertical takeoff & landing (eVTOL) services. In 2023 they delivered their first eVTOL aircraft to Edwards AFB and have flown their S4, a four rotor electric eVTOL vehicle in urban settings such as New York. Interestingly the S4 can also be converted to hydrogen and has flown a record 523 miles in this form! They have a couple of interesting acquisitions. The first is XWing which they acquired in 2024. XWing focuses on autonomous aircraft and in a capacity constrained aircraft, autonomy means extra space to sell. The second is Blade Air Mobility’s ride share business. Blade Air Mobility is an urban air mobility platform.
The biggest hurdle to Electric propulsion is battery density and weight. Density is expected to reach approx 400-500 Wh/kg by 2030, this clearly helps with range.
Electricity is definitely on the cusp of revolutionizing urban air mobility and this is predicted to be a $1 tn market annually by 2040. The next generation of batteries are expected to be in the 500-1000 Wh/kg range and this definitely improves range and enables larger aircraft.
Hybrid electric aircraft such as the Airbus E-Fan X bridge the gap between current technology and full electric systems, offering a path to decarbonize larger aircraft using electricity.
The Future
As of today the aviation industry is midway through its decarbonizing journey. The progress is accelerating as is seen from the advances in the last ten years. SAF has scaled from 0.1% of total ATF in 2020 to approx 0.3% or 2 billion liters.Over 400,000 flights have flown using ATF blended with SAF. By 2030 we can expect to see aircraft using 100% SAF. (Robb Report Apr’23)
Hydrogen is still in its infancy, however flights such as ZeroAvia’s 19 seater demonstrator prove feasibility. With almost a dozen aircraft in development, hydrogen powered aircraft should enter service by 2030. By 2035 we can see hydrogen powering about 15% of short haul flight below 1000 km. (ZeroAvia, McKinsey, Decarbonizing the aviation sector, Jul 2022)
Electric aircraft are on the cusp of revolutionizing VTOLs. Companies such as Joby & Archer aviation are planning commercial services by 2026.With rising battery densities , we expect aircraft applications to only increase from here. By 2050 expect eVTOls to handle 13% of all urban mobility trips rising from 5% in 2030. (Icct2020 Jul 2020)
Together these technologies are plugging critical gaps to meet the 2050 net-zero target. This means reducing aviation emissions from one billion tons per annum in 2025 to near zero. SAF with proper blending will account 65% of this with production reaching 450 billion liters by 2050. Hydrogen will complement approx 20-25% of SAFs targets by powering regional flights of below 2000km. Electric aircraft will dominate the short range (below 500km) with 20% of urban trips & 10% of regional flights covering a total of between 10-15% of total flight segments by 2050.
Collaboration & Continued Innovation is key…
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