Introduction: A Fork in the Runway
The aviation industry is at a pivotal moment. With climate imperatives intensifying, the conversation has shifted from whether aviation must decarbonize to how it can do so effectively. One term dominates this dialogue: sustainable aviation fuel. Touted as a technological fix with transformative potential, SAF has rapidly become the cornerstone of decarbonization strategies worldwide.
But what does this mean for future airport expansion projects? Is the rise of SAF a green light for growth, or a distraction from deeper structural limits? This post unpacks the nuances of SAF’s promise and examines what lies ahead for aviation infrastructure.
Understanding the SAF Proposition
A Jet Fuel Alternative Already in Use
Sustainable aviation fuel is a drop-in substitute for fossil-based jet fuel. Unlike conventional kerosene derived from crude oil, SAF sources its carbon from renewable feedstocks like plant waste, used oils, or even atmospheric CO2. Crucially, this carbon is part of the global carbon cycle rather than newly extracted from underground reservoirs.
Airports including major international hubs already use SAF in blended form. Test flights have proven the feasibility of using 100 percent SAF. On the surface, this appears to offer a ready-made solution to decarbonize flying without rethinking the fundamentals of aviation.
The Climate Calculation
SAF emits CO2 when combusted, just like fossil jet fuel. The difference lies in the lifecycle analysis. If SAF is produced using sustainable feedstocks and renewable energy, its net carbon footprint can approach zero. However, current production pathways often fall short of this ideal. In the UK, a SAF can qualify as “sustainable” even if it only achieves a 40 percent emission reduction.
Furthermore, regulations still require blending with fossil jet fuel. As a result, a flight using the maximum allowed proportion of SAF today may only cut emissions by around 20 percent compared to conventional flights.
The Scalability Challenge
Why SAF Remains a Costly Endeavour
Cost remains the biggest hurdle. The most climate-beneficial SAF types, such as e-fuels derived from captured atmospheric CO2, involve complex processes that are both energy- and capital-intensive. Studies estimate that SAF needs to be priced at 1.9 to 5 times more than fossil jet fuel to be commercially viable.
Even with technological advancements, SAF will not achieve cost parity without heavy subsidies or steep penalties on fossil fuels. This puts governments in a delicate position: promoting SAF now could entail prolonged public support, which is politically uncertain.
Limited Feedstocks and Resource Constraints
The availability of suitable feedstocks presents another bottleneck. The cheapest SAF is derived from waste oils, but this supply is inherently limited. As demand grows, producers will need to turn to more controversial sources, potentially impacting food production or ecosystems. While e-fuels offer scalability, their production demands large-scale renewable electricity, which remains a premium resource.
In short, SAF scale-up is not just a technological problem—it is a resource challenge intertwined with wider sustainability trade-offs.
Policy Optimism Meets Market Reality
Government Mandates and Industry Ambitions
Governments are setting ambitious SAF targets. The US aims for 3 billion gallons of domestic SAF by 2030. The UK and EU have binding targets of 10 percent and 6 percent SAF, respectively, by the same year. Long-term goals stretch up to 70 percent by 2050 in Europe.
Industry groups like the International Air Transport Association expect SAF to deliver nearly two-thirds of emissions reductions needed for net zero. These plans assume a massive acceleration of SAF supply—an outcome that remains far from guaranteed.
A Delicate Balancing Act
The problem is not that SAF lacks potential—it is that SAF cannot singlehandedly deliver a low-emissions aviation sector without deeper systemic change. At best, it can be one piece of the puzzle. At worst, over-reliance on SAF risks deferring necessary policy discussions about demand, infrastructure, and behavioural change.
Beyond CO2: The Contrail Conundrum
Even if SAF were entirely carbon-neutral, it would not address all of aviation’s environmental impacts. Aircraft emissions include nitrogen oxides and water vapour, which contribute to warming through contrail formation. These effects are significant—contrails alone may have contributed as much warming as all historic aviation CO2.
Early research suggests SAF might reduce contrail-related impacts by up to 44 percent, but this is still a partial mitigation. It underlines a key message: technological solutions cannot fully offset aviation’s planetary footprint.
What This Means for Airport Expansion
The Heathrow Case
Heathrow, the UK’s largest airport, is a key focus of expansion debates. It consumes nearly half of the UK’s aviation fuel and contributes a similar share of aviation emissions. Proponents of expansion cite SAF as a climate-compatible growth enabler. Yet such assertions rest on uncertain assumptions about future SAF availability and cost.
If the SAF transition falters—or proves too costly to scale—then airport growth may contradict national climate commitments. Betting on SAF without acknowledging its limits risks locking in unsustainable infrastructure that becomes incompatible with future environmental goals.
The Broader Insight: Decarbonisation Cannot Be Deferred
The debate over SAF reveals a deeper truth. Decarbonising aviation cannot hinge on a single innovation, no matter how promising. Instead, it calls for a holistic strategy—combining cleaner fuels, demand management, smarter routing, and fair economic instruments.
Infrastructure decisions made today will shape emissions for decades. Prioritising flexibility, caution, and compatibility with a low-carbon future is not just prudent—it is essential. Any airport expansion plan must pass this test.
Conclusion: Towards Informed Optimism
SAF offers real value. It is a tangible step toward cleaner flying, already in motion, with room for improvement and scaling. However, its transformative potential is constrained by persistent cost and resource barriers that are unlikely to disappear.
Recognising SAF’s limitations is not pessimism—it is realism. And realism is the best foundation for sustainable progress in aviation. As the industry and governments navigate future airport developments, it is crucial that ambition is matched by accountability. The future of flight must be not only cleaner but also smarter. The skies may remain busy, but the path forward demands clarity at every altitude.