Sustainable Aviation Fuel

What Is SAF and Why Does It Matter for the Future of Aviation Engineering?

Aviation accounts for around 2.5% of global CO2 emissions. However, when non-CO2 effects — contrails, water vapour and particulate emissions at altitude — are included, its total climate impact rises to an estimated 3.5–4% of global warming when non-CO2 effects are included — roughly 1.5 times its CO2 contribution alone. Decarbonising aviation is therefore one of the most technically demanding challenges the engineering world faces. Hydrogen-powered and battery-electric aircraft offer long-term potential. However, they remain decades away from commercial scale. Sustainable aviation fuel — SAF — offers a practical, near-term solution that works within existing aircraft and infrastructure.

Furthermore, it is not simply an environmental story. SAF represents a fundamental shift in fuel chemistry, production engineering and supply chain design — with significant implications for precision engineering businesses across the aerospace sector.

What Sustainable Aviation Fuel Actually Is

SAF is an alternative to conventional jet fuel. It produces the same chemical hydrocarbons as kerosene — but from non-petroleum feedstocks. These include used cooking oil, animal fats, agricultural waste, municipal solid waste, captured CO2 and low-carbon hydrogen.

The critical engineering advantage of SAF is its compatibility with existing systems. It meets the same ASTM international fuel specifications as conventional jet fuel. It drops into existing aircraft engines, fuel systems and airport infrastructure without modification. Furthermore, current certification allows SAF to blend with conventional jet fuel at up to 50% by volume — with ongoing work toward 100% SAF certification for future aircraft. As a result, airlines can introduce SAF immediately without waiting for new aircraft or new infrastructure.

On a full lifecycle basis, SAF reduces greenhouse gas emissions by up to 80% on a full lifecycle basis compared to conventional kerosene. That figure accounts for the carbon embedded in the feedstock, the energy used in production and the emissions from combustion. It is not a small improvement. It represents the single largest lever available to aviation for near-term carbon reduction.

How SAF Is Produced — The Four Main Pathways

SAF production is not a single process. Several distinct engineering pathways convert different feedstocks into aviation-grade fuel. Each has different maturity levels, feedstock requirements, production costs and scalability characteristics.

HEFA — Hydroprocessed Esters and Fatty Acids
HEFA is currently the most mature and widely deployed SAF pathway. It converts used cooking oil, animal fats and vegetable oils into synthetic paraffinic kerosene through hydrotreating and hydroisomerisation. The process is well understood and relatively straightforward. However, feedstock availability limits how much HEFA the world can produce. Used cooking oil and animal fats are finite resources. Therefore, HEFA alone cannot deliver SAF at the scale aviation requires.

Fischer-Tropsch Synthesis
The Fischer-Tropsch process converts carbon-rich feedstocks — municipal solid waste, biomass residues or captured CO2 — into synthesis gas, then into liquid hydrocarbons through catalytic reaction. The result is a high-quality fuel that meets aviation specifications. Moreover, FT synthesis is highly versatile. It accepts a wide range of feedstocks and can integrate with the power-to-liquids pathway. UK companies including Green Lizard Technologies and Avioxx are actively developing Fischer-Tropsch SAF production systems. Green Lizard operates an industrial-scale FT system at a 500-acre site in Teesside — converting CO2 directly into SAF.

Alcohol-to-Jet
The alcohol-to-jet pathway ferments or gasifies cellulosic and waste feedstocks to produce alcohols — typically ethanol or isobutanol — then upgrades them chemically into aviation-grade hydrocarbons. It expands the feedstock base further but requires more complex processing steps than HEFA.

Power-to-Liquids
Power-to-liquids is the most advanced and potentially most scalable long-term pathway. It combines captured CO2 and low-carbon hydrogen — produced using renewable electricity — to synthesise aviation fuel with very low lifecycle carbon intensity. In principle, it requires no biological feedstock at all. Consequently, it avoids the land use and feedstock competition issues that constrain bio-based pathways. However, it currently requires significant amounts of renewable electricity and remains more expensive than other routes.

The UK Regulatory Landscape

The UK introduced a SAF mandate on 1st January 2026. At least 2% of all jet fuel on flights departing UK airports must now be SAF by law. That target rises to 10% by 2030 and 22% by 2040. Government figures project that this trajectory delivers up to 6.3 megatonnes of carbon savings per year at the 2040 level.

The Department for Transport funds the UK SAF Clearing House — a programme that helps SAF developers access government support, navigate certification requirements and connect with testing facilities. In January 2026, the government awarded £181,000 to four UK SAF innovators — Avioxx, Clean Planet Technologies, Green Lizard Technologies and Zero Petroleum — to accelerate testing and certification of next-generation fuels.

Furthermore, the government plans to introduce a Revenue Certainty Mechanism by the end of 2026. This sets a strike price for SAF over a defined period. If the market price falls below the strike price, government compensates producers — shielding them from market shocks and giving investors the confidence to commit capital to new production facilities. Therefore, the UK policy environment is actively working to de-risk SAF investment and accelerate domestic production capacity.

The Engineering Challenges of Scaling SAF

The chemistry of SAF is well understood. The engineering challenge is scale. Global aviation currently consumes around 300 million tonnes of jet fuel per year. According to IATA, SAF currently accounts for around 0.53% of that total. Closing that gap requires a transformation in production engineering — not simply an incremental increase in existing capacity.

Building new SAF production plants demands precision process engineering, chemical reactor design, materials handling systems and extensive test and validation infrastructure. Fischer-Tropsch reactors operate at high temperatures and pressures. They require precise control of synthesis gas composition, catalyst management and product separation. Moreover, each new production pathway brings its own specific engineering requirements. Power-to-liquids facilities require large-scale electrolysis systems, CO2 capture infrastructure and fuel synthesis reactors — all of which must be designed, built, tested and certified to industrial standards.

In addition, the fuel itself requires rigorous testing and certification at every production stage. Each batch must demonstrate that it meets aviation fuel specifications before it enters the supply chain. Test rigs, analytical instrumentation and precision measurement systems are therefore essential infrastructure for any SAF production programme — not optional additions.

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SAF and the Broader Aerospace Engineering Opportunity

SAF is not simply a fuel story. It is an engineering story. New production facilities require specialist process and mechanical engineering. New fuel blends require testing against existing and next-generation engine architectures. Aircraft manufacturers — Airbus has committed to 100% SAF-capable aircraft by 2030 — need test infrastructure to validate engine and fuel system performance across the full blend range.

Furthermore, the Royal Aeronautical Society estimates that around 65% of the carbon reductions needed to meet aviation’s net zero 2050 target will come from SAF. That makes it not just one tool among many — but the central engineering solution for decarbonising flight over the next three decades.

The engineering disciplines that SAF demands — precision mechanical design, chemical process engineering, test rig development, instrumentation and measurement — are the same disciplines that precision engineering consultancies apply across aerospace and energy programmes every day. As the UK’s SAF industry scales from demonstration plants to commercial production, the demand for that engineering capability will grow significantly alongside it.