Qualification of sustainable aviation fuels: system constraints and opportunities for scale

Abstract

Sustainable aviation fuels (SAF) are widely recognised as a key component of aviation decarbonisation strategies. However, the introduction of new fuels into a safety-critical aviation system requires robust evaluation to ensure compatibility with existing aircraft, engines and fuel infrastructure. This review examines the qualification of synthetic aviation turbine fuels within established qualification and certification frameworks, with a focus on how the ASTM D4054 evaluation process operates in practice and how it interacts with broader factors influencing SAF deployment. The paper analyses how differences in fuel composition, including bulk properties, trace species and performance characteristics, are translated into proportionate evidence requirements through a structured, risk-based approach. It highlights that qualification is not a prescriptive sequence of tests, but a distributed evidence-generation and governance process involving fuel developers, testing organisations, original equipment manufacturers, standards bodies and other stakeholders. As the diversity and maturity of synthetic blend components increases, the performance of the qualification system is shaped not only by intrinsic technical uncertainty, but also by structural factors including testing infrastructure, representative fuel availability, data quality, OEM review capacity and stakeholder coordination. The review distinguishes clearly between fuel qualification and deployment. For several established pathways, qualification has not generally been the primary constraint on SAF uptake; deployment remains strongly influenced by feedstock availability, production scale, economics, infrastructure and policy certainty. However, the complexity, timescales and cost of evaluation can still influence pathway accessibility, particularly for more novel fuels, highlighting the need to improve qualification efficiency without compromising technical integrity or safety assurance. As policy ambition increases and more chemically diverse candidate fuels seek approval, qualification may become a more material constraint on the pace, predictability and diversity of future SAF deployment. Drawing on developments in pre-screening, distributed testing, Clearing House coordination, qualification-readiness assessment, data standardisation and proportionate evaluation approaches, the review shows that the qualification system is evolving to improve efficiency and scalability while maintaining the requirements of safety, operability and long-term system integrity. Overall, the paper positions fuel qualification as an enabling component of the SAF ecosystem whose future scalability will depend on earlier uncertainty reduction, improved data generation, coordinated testing infrastructure and continued expert review.