Tell us about the CAA’s Hydrogen Challenge and what it aims to achieve.

“The UK CAA’s Hydrogen Challenge is a cross-industry innovation programme focused on enabling the safe introduction of hydrogen as an aviation fuel. Launched in 2023, it brings together regulators, industry, academia and government to better understand the opportunities and challenges associated with hydrogen-powered flight.

“The aim is not to promote a particular technology, but to ensure that if hydrogen becomes a significant part of aviation’s future, the regulatory framework is ready. Through the programme, we’re identifying safety risks, assessing where regulations may need to evolve, and creating opportunities for real-world testing and learning through the Hydrogen Sandbox. Ultimately, the goal is to improve regulatory readiness and support informed decision-making on the pathway toward net-zero aviation.”

What are the biggest regulatory and certification gaps currently facing hydrogen propulsion in aviation?

“One of the biggest challenges is that hydrogen fundamentally changes some of the assumptions that underpin today’s aviation regulations. Existing certification frameworks were developed around conventional fuels and propulsion systems.

“Key gaps include certification requirements for hydrogen fuel-cell and hydrogen-combustion propulsion systems; standards for onboard hydrogen storage, distribution and crashworthiness; airport infrastructure requirements for hydrogen production, storage and refuelling; operational procedures, maintenance practices and emergency response arrangements; and defining how safety evidence should be generated and accepted for novel technologies.

“While many aviation safety principles remain applicable, regulators globally need additional data, operational experience and standards to support certification at scale.”

Tell us about the Hydrogen Sandbox and what early insights it’s uncovered so far.

“The Hydrogen Sandbox is a controlled environment where organisations can work directly with the regulator to test concepts, assess safety cases and explore regulatory questions before commercial deployment. The first rounds involved aircraft developers, airport operators, infrastructure specialists and researchers working collaboratively with the CAA.

“Some early insights include the value of bringing regulators into development programmes early, rather than waiting until certification; the importance of considering the entire hydrogen ecosystem, not just the aircraft; the need for clear interfaces between aviation regulations and other sectors such as energy, industrial gas handling and hazardous materials management; and the benefit of safety assessment methods, such as bowtie analysis and systems-based approaches, to identify hazards and mitigations early in the design process.

“The CAA has recently published a hydrogen roadmap to 2025 providing a long-term view of how regulation will need to evolve to support hydrogen-powered aviation safely. The Sandbox has also demonstrated how real-world testing can accelerate learning for both industry and the regulator.”

Why is cross-industry collaboration so critical to achieving regulatory readiness for hydrogen aviation?

“Hydrogen aviation is not simply an aviation challenge; it’s a systems challenge where success depends on aircraft manufacturers, propulsion developers, airports, fuel suppliers, infrastructure providers, emergency services, academia and regulators all working together. No single organisation has all the expertise required.

“The Hydrogen Challenge has shown that collaboration helps identify risks earlier, avoids duplication of effort and creates a shared understanding of what safe implementation looks like. Importantly, it allows regulators to develop evidence-based approaches while industry gains clarity on future certification and operational expectations.

“This collaborative approach will be essential if the UK is to help shape international standards for hydrogen aviation.”

What would you say are the main safety challenges unique to hydrogen propulsion, compared to conventional aviation fuels?

“Hydrogen has very different physical properties from conventional aviation fuels, which creates both opportunities and challenges.

“Some key areas include safe storage of hydrogen, particularly cryogenic liquid hydrogen; prevention and detection of leaks; managing ignition risks and understanding hydrogen flame behaviour; safe refuelling operations and ground handling procedures; integration of hydrogen systems into aircraft designs while maintaining appropriate levels of redundancy and resilience; and ensuring airports and emergency responders are equipped with the right procedures and training.

“What’s important to emphasise is that these are engineering and operational challenges that can be managed, but they require robust evidence, testing and regulatory oversight.”

How realistic is the goal of safe commercial hydrogen aviation by 2035, and what needs to happen to get there?

“The 2035 ambition is challenging but achievable for certain segments of the market, particularly regional and short-haul operations.

“The industry has already made significant progress, with hydrogen-electric systems, ground demonstrations and flight-test programmes delivering valuable data. However, success will depend on several factors: continued technology maturation; timely development of certification frameworks; investment in hydrogen infrastructure at airports; international alignment of standards and regulations; and ongoing demonstration activities to build the evidence base needed for safety approval.

“The key message is that safety must remain the primary driver. The pace of adoption will ultimately be determined by the evidence provided for supporting safe operation.”

What can attendees expect to take away from your session at the Testing Forum?

“Attendees will gain an overview of how the CAA is approaching hydrogen aviation from a regulatory and safety perspective, and why regulatory readiness is just as important as technological readiness.

“We’ll share lessons learned from the Hydrogen Challenge and Hydrogen Sandbox, highlight emerging regulatory considerations, and discuss how testing and demonstration activities are helping build the evidence needed for future certification and operations.

“Most importantly, attendees will understand how collaboration between regulators, developers, airports and researchers is helping create practical pathways toward safe commercial hydrogen aviation.”

Is there anything else you would like to add?

“The Hydrogen Challenge demonstrates how regulators can engage proactively with innovation, helping industry understand regulatory expectations while building the knowledge needed to make informed decisions. By working together now, we can help ensure that future hydrogen aviation is not only sustainable, but also safe, scalable and publicly trusted.”