The Achilles’ heel of stealth flight: Contrails
Stealth aircraft are engineered to be undetectable - by radar, infrared, and acoustic tracking. Their shapes deflect signals, their coatings absorb energy and their engines are masked and cooled; but they still have one glaring weakness: contrails.
Contrails are the white streaks left behind as jets cut across the sky and are formed when hot engine exhaust hits cold, humid air. Water vapour condenses into ice crystals, clinging to soot and particulates in the exhaust. They are bright, long-lasting, and easily visible from the ground and space.
For stealth missions, they’re a major liability. Contrails reveal the location, altitude, and direction of aircraft that were otherwise built to vanish. In daylight or clear skies, they negate decades of stealth innovation in seconds.
Synthetic fuel solves this.
Avioxx Sustainable Aviation Fuel (SAF), made from non-recyclable waste materials, contains fewer particulates due to its manufacturing process. It burns ultra-clean and leads to a dramatic reduction in contrail formation.
Recent batches of synthetic Fischer–Tropsch (FT) crude produced at our advanced fuel research facility were found to be virtually free from impurities, notably sulphur compounds and aromatics which are the main contributors to soot and ice-nucleating particles. This ultra-low contaminant profile has been independently validated by Intertek under the UK Department for Transport’s SAF Clearing House programme.
By minimising particulate emissions at source, Avioxx SAF offers a material reduction in contrail formation potential, further enhancing its climate benefit beyond CO₂ reduction alone.
A strategic advantage in plain sight
To avoid leaving visible contrails, stealth aircraft pilots often resort to suboptimal flight paths, flying at lower altitudes where temperatures are warmer and avoiding areas of high humidity. These tactics significantly increase fuel consumption and reduce the operational range of the stealth mission.
Avioxx Sustainable Aviation Fuel (SAF) changes that by eliminating the root cause of contrails through the ultra-clean synthetic fuel produced, which allows stealth aircraft to operate freely.
The innovation and large-scale production of SAF is essential to support the continued growth and operational effectiveness of stealth missions, reducing their risk of being detected by contrails and giving them the operational advantage whilst also having environmental benefits.
SAF: high performance, low visibility
Avioxx SAF isn’t just sustainable, it’s superior. Our synthetic fuel offers higher energy density than conventional Jet A1, enabling longer range flights and improved efficiency. Its ultra-clean combustion reduces engine wear and cuts harmful emissions whilst also minimising contrail formation. With cost competitiveness achievable at scale, Avioxx SAF is engineered for real-world deployment for both military and civil applications.
The adoption of SAF in defence
NATO air forces are now testing and piloting SAF blends, particularly the US Air Force and the RAF. Whilst widescale use is still in development, the shift towards SAF integration is accelerating, driven by evolving policies and companies like Avioxx demonstrating both the tactical and environmental benefits of fuel alternatives.
In the UK, the Ministry of Defence has mandated that all aviation fuel procured from 1 January 2025 must include SAF. This makes the UK the first NATO country to mandate SAF inclusion in defence aviation. As part of this policy, the RAF, including Typhoon and Voyager aircraft at RAF Lossiemouth, began routine use of SAF blends in 2024, with over 9 million litres delivered. The Red Arrows flew the 2025 King's Birthday Flypast using 100% sustainable fuel, marking a historic moment in clean defence aviation.
"Through our use of renewable fuel options... we are demonstrating the best of science, technology, engineering and maths," - James Appathurai, Deputy Assistant Secretary General for Innovation, Hybrid and Cyber 6
What’s next
Contrails are not yet regulated - but that’s changing. Their climate impact is now measurable and unavoidable in long-term aviation policy. The UK’s leading research programmes, from the GRIM‑SAF chase plane campaign to COBALT and the ATI Non‑CO₂ Roadmap, are zeroing in on soot-driven contrail formation as a critical challenge for climate and defence.
Avioxx SAF offers a direct, practical solution to making defence aviation not only more sustainable but also safer. While contrail-focused startups like Satavia, Metron Aviation, and Cambridge-based Aether work on routing optimisation and post-flight analysis, Avioxx tackles the problem at the engine exhaust, eliminating the particulates that contrails need to form in the first place.
This isn’t theory - it’s proven chemistry, confirmed performance, and operational readiness. Our SAF is not just a climate win but a strategic advantage. Our fuel gives military aircraft the freedom to stay at altitude, follow optimal flight paths, and minimise exposure - without compromise.
Backed by UK travel leader Trailfinders, Avioxx is scaling a SAF solution that serves commercial, operational, and national interests - where cleaner also means safer.
1 https://en.wikipedia.org/wiki/Stealth_aircraft
2 https://thegunzone.com/why-do-military-jets-not-leave-contrails/
3 https://www.flightglobal.com/fixed-wing/us-military-to-explore-use-of-sustainable-aviation-fuel/
4 https://ukdefencejournal.org.uk/military-fuel-to-include-sustainable-aviation-fuel-from2025/
5 https://apps.dtic.mil/sti/tr/pdf/ADA240467.pdf
6 https://www.boeing.co.uk/news-releases/2024/boeing-provides-guidance-on-saf-usage-for-def
7 https://www.raf.mod.uk/display-teams/red-arrows/news/red-arrows-make-history-with-sustaina/