• 23 Jun 2025 12:52 PM
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Hydrogen Aviation: Pushing the Envelope

By Mike Hirschberg and Jesse Schneider
Vertiflite, July/August 2025

This is a slightly expanded version of the article published in the July/August 2025 issue of Vertiflite magazine. For more on the progress and challenges of hydrogen aviation, check out the VFS resource page at www.eVTOL.news/hydrogen. (Above: Participants at the end of the 4th Annual H2-Aero Symposium. VFS photo.)

The Vertical Flight Society held its fourth annual H2-Aero Symposium on April 2–3, 2025, in Long Beach, California, with the theme, “Pushing the Envelope.” This year's symposium featured two days of groundbreaking presentations with the latest cutting-edge developments by the who's who of the hydrogen aviation and fuel cell community, including presentations on hydrogen, fuel cell, and aerospace technologies; regulations; aircraft demonstrations; and hydrogen hubs for airports.

More than 100 in-person attendees (plus two dozen online) were present for a number of world-first presentations and announcements, as well as technological insights on the progress and challenges of hydrogen aviation.

Kick-Off Keynotes
The annual VFS event kicked off on April 2 with an introduction by the H2-Aero Symposium Chair Jesse Schneider, CEO/CTO of ZEV Station. His presentation, “Decarbonizing Aerospace and Airports with Hydrogen,” highlighted the role of synergies in decarbonizing ground and air transportation, as well as creating multimodal hydrogen airport hubs and building a community for industry, academia and government entities to work together.

Despite uncertainty in US federal transportation strategy, California continues its push for all light- and medium-duty vehicles to be zero emissions vehicles (ZEVs) by 2035. Already 25% of all light-duty vehicles are ZEVs. The state is also planning to reach 100% carbon-neutral electricity by 2045, with its grid already at 33%. Relevant to the VFS symposium, California also has $12.6B (including up to $1.2B in federal funding) for its Alliance for Renewable Clean Hydrogen Energy Systems (ARCHES), one of the US hydrogen hubs. It also has planned an H2-Aviation whitepaper to be published in 2025.

Schneider highlighted that “it takes a village” in decarbonizing aviation and airports. This includes the aerospace industry, certification bodies, technology companies, standards development organizations (SDOs), academia and government research laboratories. He also highlighted the white paper developed after the first H2-Aero Symposium in 2023. Scheider led the H2-Aero team that published the VFS whitepaper, “Multimodal Hydrogen Airport Hub,” which outlined a ground vehicle and aircraft hydrogen hub as a model to commercialize a hydrogen airport. This effort spawned the creation of the SAE International AE-5H Hydrogen Airport Committee (see below).

The first keynote was given by Dr. Val Miftakhov, CEO of ZeroAvia, reporting on the company’s groundbreaking progress toward commercialization. He stressed the significant public health impacts from the combustion of fossil fuels — beyond carbon dioxide (CO2) to include ultrafine particles (UFP), nitrogen oxides (NOx) and sulfur oxides (SOx). Hydrogen-electric propulsion is seen as the most scalable approach for aviation, he said, with the major challenges being the high powertrain weight and the fuel tank volume required. Sustainable aviation fuel (SAF), while it can generally be used as a drop-in replacement for conventional jet fuel to reduce the amount of pollution, is not scalable, he said, because there isn’t enough sustainable biofuel available, nor will there be in the future.

Miftakhov highlighted ZeroAvia’s track record of delivering world-first breakthroughs in hydrogen aviation. In 2020, ZeroAvia flew the world’s largest hydrogen-electric flight with a six-seat Piper M-Series aircraft, and then broke that record in 2023 with a 19-seat Dornier 228, with one turbine engine replaced with a hydrogen fuel cell system. This allowed ZeroAvia to complete the flight test campaign of its ZA600 propulsion system in 2024, finalizing the design. The ZA600 uses gaseous hydrogen (GH2) storage for a low-temperature proton exchange membrane (LTPEM) and a 660-kW electric motor for small turboprop aircraft.

The UK Civil Aviation Authority (CAA) is the lead on powertrain and integration, while the US Federal Aviation Administration (FAA) is planning on concurrent validation and is the lead on the electric propulsion system (EPS); the European Union Aviation Safety Agency (EASA) is planning for sequential validation.

ZeroAvia announced in February that it had received a G-1 issue paper (stage 2) for the EPS from the FAA; this means that the government and ZeroAvia have agreed upon the basis for certification. “Certifying and selling our 600kW electric propulsion system helps ZeroAvia expand our addressable market and increase our impact in pursuit of a clean future of flight,” Miftakhov said in the press release.

The company is planning for a 2026 entry-into-service, with the certification process well underway. Once the ZA600 and the EPS is certified, it can replace turbine engines through a supplemental type certificate (STC). The company says the ZA600 will have high fault tolerance, substantial noise reduction and up to a 40% reduction in operating costs as a zero-emission replacement for turbine engines.

The company is also working on its ZA2000, which uses liquid hydrogen (LH2) for a high-temperature proton exchange membrane (HTPEM) and a 2-MW+ motor for larger applications. Beyond 2030, HTPEM-based systems could power regional jets and narrowbody aircraft.

Dr. Martine Rothblatt, CEO of United Therapeutics, a novel company developing manufactured organs for transplants, revealed the company’s pioneering success in flying the world’s first piloted hydrogen fuel cell-powered electric vertical takeoff and landing (VTOL) aircraft, a modified Robinson R44 helicopter. The UT H2eR44 made its first flight in Bromont, Québec, Canada, on March 27, 2025. The three-minute, 16-second test flight demonstrated the hover and maneuvering capabilities of the hydrogen powertrain, as described in the last issue (see “World’s First Piloted Hydrogen VTOL Lifts Off in Québec,” Vertiflite, May/June 2025).

The H2eR44 first began ground testing in December 2023, as announced at the VFS 80th Forum in May 2024 (see “Hydrogen Begins to Take Off,” Vertiflite, July/Aug 2024). The company’s near-term goals are set at a 200-nm (370-km) range with a 500-lb (227-kg) payload. The power management system, used to control the combination of energy from the fuel cells and the booster batteries to meet the transient power requirements during takeoff and landing, was a significant breakthrough. Their first fuel cell system achieved a peak output of 178 kW, with hover shaft power around 155 kW. This was achieved using two 92 kW fuel cell stacks and a 45-kW peak-rated booster battery. The storage onboard was 4.5 kg (9.9 lb) in gaseous storage. The company plans to change to an LH2 system using a vacuum-insulated, dual-shell, carbon fiber tank built by Gloyer-Taylor Laboratories (GTL), described below.

Extensive work was required to optimize the external cooling system needed to dissipate heat from the fuel cells when hovering, with fans installed in a large nacelle on either side of the fuselage. The power management system, used to control the combination of energy from the fuel cells and the booster batteries to meet the transient power requirements during takeoffs and landings, was a significant breakthrough. Rothblatt said UT will work to develop an STC for the larger R66 for a carbon-free organ delivery system.

Certification
A key challenge for the commercialization of hydrogen for aviation is certification. To find ways together to tackle this challenge, the FAA, CAA and EASA are working closely together with a roadmap on certification, with EASA in the lead.

Dr. Catalin Fotache, the FAA’s Chief Scientist and Technical Advisor for Propulsion Systems, chaired a session with representatives of the three regulators, calling in live from Europe. CAA Zero Emissions Flight Lead Helen Leadbetter and Colin Hancock — Department Head of Policy, Innovation and Knowledge in the EASA Certification Directorate — presented detailed explanations of their organizations’ plans.

Fotache presented the FAA’s Hydrogen-Fueled Aircraft Safety and Certification Roadmap, which was published in December. The roadmap was developed because several companies were applicants for aircraft type certification (TC) with hydrogen propulsion and because of the Congressional mandate in the FAA Reauthorization Act of 2024. The roadmap is a plan to identify and address the regulatory issues associated with safely and efficiently incorporating hydrogen as an energy source in aircraft.

Fotache also highlighted some of the unique challenges associated with hydrogen that will be addressed as part of certification. Although hydrogen has a gravimetric density that is more than a hundred times better than batteries and nearly three times greater than jet fuel, the volumetric density is only slightly better than batteries and much lower than jet fuel. Thus, hydrogen aircraft will require much larger tanks for both GH2 and LH2 storage.

Although hydrogen is in many ways safer than fuels like gasoline, it has different hazard properties. Hydrogen is highly combustible in certain conditions, and even very small leaks will sustain a flame, with microflames being very difficult to detect. “We must treat it with respect,” he warned.

Significant work remains in order to develop the certification regulations. Working groups and SDOs are looking at the certification gaps and how to fill them. The FAA announced in December that it would form a Hydrogen Aviation Working Group (HAWG), supporting the FAA’s Aviation Rulemaking Advisory Committee (ARAC); however, with the Trump administration restricting the FAA’s interactions with industry, this effort is currently suspended.

Fotache concluded by highlighting that the safety roadmap and the technology research and development (R&D) are just the initial steps. “Much work remains, not least in coordination” between the world’s regulatory bodies and SDOs (such as SAE), but “Hydrogen in aviation is here already and likely to stay.”

One audience member asked how the community should respond when people say, “The FAA will never certify a hydrogen airplane,” as a result of what’s been named the “Hindenburg Syndrome.” Fotache rejected this statement but stated simply that “the FAA will never certify an unsafe design.”

Hancock covered EASA’s Hydrogen Certification Roadmap. EASA expects that electric general aviation aircraft, electric VTOL aircraft and regional air mobility aircraft will be certificated by 2030, with some powered by hydrogen fuel cells. By the late 2030s, larger regional and single-aisle hydrogen-powered aircraft developed for mass-transit, short-haul markets will follow. After 2040, EASA sees the potential for hydrogen-powered longer-range aircraft.

To accommodate these commercial developments, EASA developed a working group on hydrogen with the FAA in October 2023 and has been working on an extension to the working group involving the other major western certification authorities. The EU has been funding research into hydrogen propulsion for many years through its Clean Aviation program (the follow-on to the Clean Sky joint undertaking). In 2022, the EU launched the Alliance for Zero Emission Aviation (AZEA) to “prepare the aviation ecosystem for the entry-into-service of hydrogen and electric aircraft.” AZEA has more than 180 members representing industry, SDOs and certification agencies; research bodies; environmental interest groups; and regulators.

EASA, FAA and CAA are considering three different certification options. The entire propulsion system — comprising the tanks, fuel cell, distribution systems and electric motors — could all be certificated under the FAA Part 33/EASA CS-E engine TC standard. Or an engine TC could be granted only to the power management, electrical distribution and electric motors, while the tanks and fuel cell are certificated with the aircraft. A third option is to certify the aircraft and the full propulsion system with one TC; however, this would preclude the hydrogen system from being used on other platforms without it being recertified as part of that aircraft.

Like Fotache, Hancock highlighted the hazards and safety R&D needs:

• Fire and Explosion: leak detection; fuel shutoff and relight; safe venting; flammability and fire under flight conditions; detonation, including within the powerplant; and cabin evacuation
• Crashworthiness: inspection and maintenance procedures, survivable crash conditions and surrounding structure that may contribute to the rupture of the tank
• Material: embrittlement and diffusion at altitude, extreme thermal cycling, purging and fuel cell membrane durability
• Other: lighting and electrical faults; high-voltage management, thermal management system, tank sloshing pressure collapse, cryogenic system and liquid-to-gaseous hydrogen conversion

Specific to crashworthiness, Hancock emphasized the EASA’s objective that aircraft occupants should have every reasonable chance of escaping serious injury and quickly evacuating the aircraft following otherwise survivable crash conditions. Hydrogen-specific threats include fire and explosion, cryogenic hazards, hypoxia due to leaks into occupied areas and high-voltage shock. When designing hydrogen-fueled aircraft, “Passengers should have at least the same level of survivability compared to an equivalent aeroplane with conventional fuel.”

Leadbetter explained the UK CAA “Hydrogen Challenge” was launched in 2023 to facilitate collaboration with industry and academia to improve understanding of hydrogen-related risks in aviation, identify gaps in policies and propose new recommendations to develop net-zero policies. Funding awards were made to Cranfield Aerospace Solutions, which is developing a hydrogen fuel cell powertrain to be applied to aircraft; Exeter Airport Consortium, which is reducing the environmental impact of aircraft turnarounds there; and ZeroAvia, which is developing hydrogen-electric engines for aviation. A second round of funding is now going to 13 participants to cover the gamut of hydrogen fuel cells; combustion; fuel systems; airports; general aviation; uncrewed aircraft systems (UAS); and high-altitude pseudo-satellites, such as lighter-than-air (LTA) aircraft.

Within the Hydrogen Challenge Sandbox, the CAA has three major workstreams:

• Safety: Conducting a safety risk assessment for hydrogen fuel cells and hydrogen airports, including for aircraft and ground support equipment, as well as air and ground crew safety training
• Policy and Regulation: Reviewing the gaps in certification requirements for hydrogen fuel cell drivetrains and developing policy recommendations
• Testing: Ground testing and flight testing

The challenge is also funding academic research into hydrogen combustion and the effects of hydrogen on materials.

Advances in Hydrogen Technologies
A session on hydrogen aviation technologies featured talks by three companies developing innovative technologies.

Andreas Bodén, CTO of PowerCell Group — based in Göteborg, Sweden — highlighted the company’s past, present and future. Spun out of the Volvo Group in 2009, PowerCell has more than 30 years of fuel cell R&D and intellectual property and is currently working on 24 projects in aviation. In addition to consulting, support and modifications, PowerCell has two current fuel cell stacks — the S2 (3–35 kW), with a wide range of applications for marine, power generation, off-road and on-road vehicles, and the S3 (75–150 kW), which is used for aviation.

At the H2-Aero Symposium, PowerCell unveiled a mock-up of its 300-kW HDS300 stack, which it calls an intermediate temperature proton exchange membrane (ITPEM) fuel cell, with a temperature of 105°C (221°F). The ITPEM is higher performing than a LTPEM but more mature than the HTPEM and has shown reliable performance at elevated temperatures: “Leveraging a foundation of industrialized, validated technology, the HDS300 stack is progressing toward industrial readiness and is aligned with upcoming deployment phases for small- to medium-sized aircraft,” Bodén stated in his slides.

Bodén also described the Clean Aviation’s €44.8M ($49.7M) “NExt generation high poWer fuel cells for airBORNe applications” (NEWBORN) project. PowerCell is one of 13 partners working on the 3.5-year EU project. The goals are to test a ground demonstrator in 2026 for a design that could be scalable for 1–8-MW applications from small airplanes to airliners.

Chris Gilmore from Honeywell’sTechnology Strategy Group, responsible for engines and power systems, spoke about the company’s developments in the 100-W to 1-MW range. The company has seen that small UAS with fuel cells can have up to three times the range over batteries. Hydrogen’s superior energy density enables beyond-visual-line-of-sight (BVLOS) missions with clean, quiet and reliable power. It reduces the need for lithium battery charging and transportation, and longer endurance can equate to lower cost. The company is developing a 1.2-kW, liquid-cooled GH2 system for UAS, with parallel (redundant) or series (high-voltage) options. Honeywell is now also studying solid-state fuel cells, stating that there’s an 80% bill-of-materials commonality with compressed GH2 fuel cells, with the fuel and fuel systems obviously being very different. Although still in the laboratory test phase, the performance of solid-state fuel cells is slightly higher, but would allow fuel cartridges to be transportable by air cargo, something currently not permitted for GH2 or LH2.

Gilmore noted that hydrogen for VTOL aircraft for advanced air mobility (AAM) offers a range extension without a tradeoff of emissions or noise. It would obviate the long recharge time of battery-electric aircraft but adds the complexity of hydrogen refueling. Honeywell estimated that existing AAM aircraft require 200–300 kW for cruise plus batteries for the supplemented peak power needs of vertical takeoff and landing.

Honeywell is also a partner on NEWBORN. PowerCell is developing the modular fuel cell stack, while Honeywell is responsible for the overall program and consortium leadership, system concept and integration, aircraft integration and essential systems, such as air supply, thermal management and control systems. Gilmore highlighted the overall objectives of developing a hydrogen fuel cell propulsion system, scalable from 250 kW to more than 3 MW, achieving a specific power of 1.2 kW/kg and a propulsion system efficiency of 50%. The team plans to ground-test a 1-MW system in 2026 and a flight demonstration in 2028.

GTL President Paul Gloyer highlighted the advancements in the groundbreaking capabilities of the company’s composite LH2 storage tanks, which were presented at last year’s symposium, and have shown a 75% mass reduction compared to state-of-the-art cryogenic tanks. The company’s focus over the past year has been on maturing the tank technology into a flying-capable LH2 storage and feed system. For a 42-lb (19-kg) capacity dewar tank, GTL realized a 10.5-lb (4.8-kg) reduction in the vacuum shell insulation and structure for a total tank weight of 30 lb (13.6 kg). The GTL tanks have a gravimetric index of 50–80% compared to the state-of-the-art tanks with 5–15%.

Gloyer presented the LH2 system that it delivered for a full cell-powered electric helicopter (later confirmed to be the United Therapeutics H2eR44), as well as a pylon-mounted tank design. GTL also provided an update of its Sentinel Ultra-Long Endurance Drone concept. The LH2 system would provide 20 times more energy per weight than an equivalent battery system, including the tanks, valves, plumbing and fuel cell. This could enable a 55-lb (25-kg) drone with a payload of 4.4–11 lb (2–5 kg) to have an operational hover time of 24–36 hours, plus reserve — two-to-three times the current world record.

The final session of the day was H2-Aero Applications, covering progress with hydrogen aircraft. Dr. Anita Sengupta, CEO of Hydroplane, gave an update on some of the company’s activities. The company’s Protium demonstrator is a replacement of a Piper Cherokee 180 leaded aviation gasoline (avgas) piston engine with a carbon-free 500-kW hydrogen fuel cell powerplant. The US Air Force has supported Protium with competitive contracts over the past several years.

Hydroplane has also received US Navy funding for a hydrogen fuel cell powerplant for mobile power generation. Hydroplane is also studying a 100–500-kW hydrogen fuel cell powerplant for mobile energy generation, which is much lighter and quieter than current diesel generators, for civil and military activities.

The US Army recently awarded Hydroplane a contract for a 480-kW fuel cell for UAS energy storage and auxiliary peak power. The Army also funded Hydroplane to explore hydrogen as primary propulsion for a helicopter, using a two-bladed kit rotor on an Enstrom 480B helicopter for a 260-kW system running on LH2.

Gad Shaanan, CEO of Unmanned Aerospace, gave an update on the company’s hydrogen-powered GH-4 VTOL gyroplane (see “Unmanned Aerospace’s GH-4 VTOL Gyroplane,” Vertiflite, Jan/Feb 2025), which has been backed by funding from the US Navy and the Office of the Secretary of Defense. The GH-4 has a 132-lb (60-kg) maximum takeoff weight and can carry a 15-lb (6.8-kg) payload up to 160 miles (260 km). Unmanned Aerospace’s larger GH-5 and CH-6 concepts would have gross weights of 360 lb (163 kg) and 750 lb (340 kg), respectively.

Shaanan noted that batteries lack sufficient energy density for long flights, so hydrogen fuel cells provide primary power. Booster batteries provide the additional power for VTOL and hover and are recharged during the low-power cruise flight segment. The hydrogen fuel cell and the unique, powered, autorotating rotor system allows the GH-4 to out-perform competing VTOL designs.

Charles Aguilar, Electric Power and Energy System Lead at Aurora Flight Sciences, presented the capabilities of the company’s Skiron lift+cruise (L+C) UAS, which has a 16.5-ft (5-m) wingspan and a cruise speed of up to 36 kt (67 km/h). Aurora installed an LTPEM fuel cell sized for the cruise power demand, augmented by a buffer battery for VTOL flight. With a battery, the maximum weight (including payload) of the Skiron-X is 49 lb (22 kg); with a fuel cell, the weight increased 10% to 54 lb (25 kg) for the Skiron-XLE. The endurance, however, doubled from 3.5 hours to 7 hours, as was demonstrated in June 2024 (see “Electric VTOL News: Aurora Flies Hydrogen UAS for Seven Hours,” Vertiflite, July/Aug 2024).

The session was completed by Dr. Neel Sirosh, CTO of H2MOF, who presented on “Reticular Material Solid-State H2 Storage Systems for Long Duration Flights.” Metal-organic frameworks (MOFs) are a class of porous polymers consisting of metal clusters coordinated to organic ligands that form reticular materials. H2MOF is developing its solid-state hydrogen-storage solution based on novel reticular materials combined with novel thermal fluid, kinetics and nano engineering. This hydrogen MOF approach has the potential to lower hydrogen delivery costs by 50–80% due to higher gravimetric, volumetric and aerodynamic efficiencies — enabling longer range/endurance and heavier payloads — as well as simplified regulations and supply chain.

Day 2 Keynotes
Keynote presentations also kicked off the second day, April 3.

Prof. Josef Kallo, cofounder and CTO of H2FLY, presented live from Stuttgart, Germany, on the company’s hydrogen-electric aircraft developments. The company’s HY4 successfully demonstrated GH2 (2016) and LH2 (2023) in flight, doubling its range to 800 nm (1,500 km). H2FLY was acquired by Joby Aviation in 2022 (shortly after the leaders of both companies attended the first VFS H2-Aero Symposium) and was part of the conversion of Joby’s battery-electric VTOL S4 into the hydrogen-electric SHY4 for a flight of 561 miles (903 km) over five hours and three minutes.

The company is now developing a 1.1–1.2-MW system for 40-seater fixed-wing regional aircraft with liquid hydrogen storage. He indicated that the target market entry for hydrogen aerospace is around 2030. Kallo noted that the noise perception for hydrogen-electric aircraft propulsion is expected to be much lower than existing turboprop engines due to the much lower frequencies generated by the lower propeller rotational speed (rpm) that result from high-torque electric motors. “In the practical world,” Kallo said, “we expect 15 dBA” in-cruise flight. H2FLY plans to enable hydrogen-electric aircraft as a powertrain system manufacturer and integrator together with Joby.

John Piasecki, CEO of Piasecki Aircraft Corporation, gave an overview of the company’s PA-890 HTPEM hydrogen fuel cell powered compound helicopter. He highlighted the HTPEM fuel cell development, which is supported by US Air Force and Department of Energy (DOE) R&D contracts under a partnership license agreement with ZeroAvia. Key benefits include five times the energy density of lithium-ion batteries and 2.5 times the specific power of LTPEMs. Compared to a turbine engine, HTPEMs have 40% higher efficiency, higher reliability with few moving parts, a longer cycle life, lower noise and zero emissions. Operating costs are also expected to be up to 50% lower than a turbine helicopter.

As announced at the first VFS H2-Aero Symposium, Piasecki Aircraft is modifying a German EDM Aerotech coaxial helicopter as a proof-of-concept flight demonstrator named HAXEL (for Hydrogen co-AXial Electric Lift). The modified two-seat helicopter has been fitted with four GH2 tanks and four hydrogen fuel cells (17 kW each), as well as a high-voltage battery for the compressor and one in-line for power buffering.

In parallel, the company has received funding from the US Air Force to build a full-scale, 660-kW fuelcell system sized for the PA-890 and run it through mission cyclic testing. This testing will help mature the hydrogen fuel cell technology at scale; validate key performance, safety and reliability; inform development of FAA certification requirements; and reduce the technical and schedule risk for its PA-890 development.

Piasecki concluded by highlighting some of the challenges that remain. These include HTPEM fuel cell technology maturity, e.g. the flow field, membrane, geometry optimization and thermal management; a very limited supply chain for aviation-grade quality systems; hydrogen fuel tank mass, volume and total fuel system cost; lack of approved FAA airworthiness criteria; and limited existing fueling infrastructure.

Finally, Dr. Arnab Chatterjee, Managing Director for Green Hydrogen and Green Fuels for NEOM (“New Future”), located in northwest Saudi Arabia, highlighted energy plans for the region. The area for the planned city on the Red Sea covers 26,500 km² (10,200 square miles) — nearly the size of Belgium — will use solar, wind and hydrogen power for clean energy. 

The NEOM Green Hydrogen Company (an equal joint venture between NEOM, Air Products and ACWA Power) is building the world’s largest green hydrogen plant, valued at $8.4B. NEOM is a 20-year project with more than 140,000 personnel currently working across NEOM’s projects; more than $40B has been expended to date. NEOM had just kicked off their first ground-vehicle hydrogen station and is planning five more in the near term. He mentioned that NEOM is planning a hydrogen hub with a production capacity of 600 metric tons per day. The hydrogen will be converted to green ammonia and delivered to locations around the world, including the US.

Safety and Standards
A session on standards and safety was moderated by Rich King, director of government and industry affairs for aerospace at SAE International, who focused on addressing gaps in hydrogen standards development. He highlighted the importance of standards development by SAE systems group and the relevant committees, which are methodical in their approach. Standards are the building blocks for performance-based regulation (PBR) that EASA, FAA and other regulators are now favoring.

King stated that regulators want industry and SDOs to lead in developing acceptable means of compliance (MOC) and guidance materials for hydrogen standards, acting as the building blocks to implementing hydrogen rulemaking and PBR. The regulator, industry associations and other nonprofits and cross-SDO engagement are key.

King highlighted the two SAE committees working on hydrogen. The SAE AE-5H Hydrogen Airport Committee has the responsibility for standardization of hydrogen at the airport, such as fueling, transport and storage.

The SAE AE-7F Hydrogen & Fuel Cells Committee focuses on developing standards and specifications for hydrogen fuel cell systems in aviation, such as fuel cell integration, storage and electrical systems. The committee also develops recommendations to support the certification of hydrogen and fuel cell systems for aircraft applications. AE-7F has already published several hydrogen standards: AS7141 Hydrogen Fuel Cells for Propulsion, AS6679 Liquid Hydrogen Storage for Aviation and AS7373 Gaseous Hydrogen Storage for General Aviation. Both committees are also joint activities with WG-80 of the European SDO, EUROCAE.

In addition to chairing the annual H2-Aero Symposiums, Jesse Schneider also chairs the AE-5CH Taskgroup, which held its annual face-to-face meeting on April 1, the day before the symposium officially started. Last year, the committee published the world’s first SAE Aerospace Information Report (AIR) publication, AIR8466 “H2 Stations for Airports Both Gaseous & Liquid Form” and is in the planning for the forthcoming AIR8999 “High Flow Liquid Hydrogen Fueling Process and Couplings for Aerospace & Heavy Transport Applications.” Future reports are planned for hydrogen-fueling safety hazard identification for aircraft; stationary hydrogen fueling; and airport hydrogen generation, distribution and safety.

In recognition of the progress being made by AE-5CH and the importance of hydrogen for aviation, SAE has recently elevated the task group to become the AE-5H Hydrogen Aerospace Committee.

Dr. Jason Damazo, lead scientist at the Boeing Research and Technology Shock Physics Lab, presented a fascinating talk on “Aircraft Safety: Jet Fuel vs. Hydrogen.” SAE AIR7765 Considerations for Hydrogen Fuel Cells in Airborne Applications (2019) concluded that, “Under normal operation, the risk of fire on hydrogen-based systems is lower than on kerosene-based ones.” However, Damazo noted that both hydrogen and jet fuel have unique characteristics that must be respected in aircraft and fueling design. For example, hydrogen has a much higher auto-ignition temperature than jet fuel, but significantly less energy is needed for an electric ignition.

Damazo highlighted that hydrogen explosions occur under a wider range of conditions at lower ignition levels and produce greater hazards, but hydrogen fires produce less radiative heating and are less dangerous to adjacent structures. In order to make hydrogen equivalently safe to jet fuel, he stated, systems are needed that are near 100% effective at preventing a flammable environment from being formed. Consideration must also be given to new fire/explosion threats (e.g., tank rupture) that aren’t normally as much of an issue for jet fuel. He indicated that his concern for safety design was “not as much for a properly designed hydrogen storage tank, but avoiding potential hydrogen leaks.”

Studies and Testing
Dr. Monterey Gardiner, Chief Engineer for Hydrogen Strategy and Partnerships at the National Renewable Energy Laboratory (NREL) Energy Conversion and Storage Systems Center, chaired the session on hydrogen studies and testing. NRELis the DOE’s primary laboratory for R&D of renewable energy, energy efficiency, energy systems integration and sustainable transportation. For transportation, NREL researches hydrogen as well as biofuels, SAF and other sustainable fuels.

NREL spans the hydrogen ecosystem, from R&D on advanced hydrogen production technologies (“make”) to infrastructure research and large-scale integration (“move”); hydrogen storage materials and systems research (“store”); and heavy-duty transportation and new end-use cases like aviation. NREL’s Fuel Cell and Hydrogen Technologies program strategy is focused on accelerating progress and impact.

NREL is now studying what hydrogen infrastructure looks like at airports. Key research objectives include estimating hydrogen demand for aircraft operations based on potential airport pairs; determining hydrogen infrastructure requirements and identifying scheduling and operational constraints (e.g., time for filling, time between fills and required state-of-charge for operations); and identifying safety considerations for hydrogen infrastructure (e.g., bulk storage location, potential hazard location, gaseous and liquid hydrogen setback distances).

Dr. Alejandro Block Novelo, the Manager for New Technologies at the International Air Transport Association (IATA) based in Montréal, Québec, presented the results of a recent study of the “Concept of Operations of Battery and Hydrogen-Powered Aircraft at Aerodromes.” The study was conducted by the Airport Compatibility of Alternative Aviation Fuels Task Force of the International Industry Working Group (IIWG) — comprising IATA, the Airport Council International (ACI) and the International Coordinating Committee of Aerospace Industries Associations (ICCAIA). The study looked at GH2 and LH2, in both fixed tanks and exchangeable, modular tanks, and identified several key knowledge gaps — such as the required refueling safety distance — that will need to be answered as hydrogen aviation matures. He highlighted that as the community develops hydrogen refueling safety guidelines, we should find a way to have an equivalent level of safety to kerosene refueling, especially related to safety distances, which is 10 ft (3m).

Finally, Dr. Vadim Lvovich, Hydrogen Aircraft Technology Lead at NASA Glenn Research Center, presented on “Cryogenic Hydrogen Studies and Testing for Advanced Aircraft at NASA.” He noted that NASA has been one of the world’s largest users of liquid hydrogen for the past 80 years, and NASA’s experience with cryogenic fuel systems for space and ground support requires development to help close the gaps in the integration of cryogenic fuel systems and propulsion into aircraft. He also noted that at a 2022 workshop at NASA Glenn, there was a strong desire for a NASA leadership role in pulling the community together on cryogenic fuels for aircraft.

Lvovich emphasized that cryogenic hydrogen systems are on a critical path for developing next-generation aircraft. NASA is exploring materials that are capable of high-cycle-life between 20°K (-424°F) and ambient temperature with low-permeability (to hydrogen) over their lifetime. Applications include lightweight, durable, volume-efficient insulation, composite materials for tanks and fluid components like pumps and valves. NASA hopes to design, implement and test tanks and cryogenic components, as well as develop facilities for collaborative hydrogen storage and testing.

Lvovich indicated that NASA has just conducted an industry survey through a request for information (RFI) related to direction for NASA hydrogen research. He said that the results should be available later this year.

Hydrogen Airports and Demonstrations
The final session of the Symposium was moderated by Dr. Jack Brouwer, Director of the Clean Energy Institute at the nearby University of California, Irvine. He gave an insightful overview of the Institute’s “Economic Feasibility Study of Deploying Clean H2 Infrastructure at Los Angeles International Airport (LAX).” The study looked at retrofitting existing aircraft or developing new hydrogen fuel cell and hydrogen combustion engines flying out of LAX, as well as hydrogen generation using mainly offshore wind and other energy sources. This groundbreaking study conducted simulations of two scenarios of hydrogen production and aircraft needs if 5% (by 2030) or 20% (by 2025) of the aircraft at LAX used hydrogen fuel. 

Ryan Kerr, fuel systems engineer at Long Beach-based startup JetZero, gave an overview of his company’s innovative blended wing body (BWB) airliner concept. He noted that SAF has near-term potential, but production rates are well below what is required for aviation’s “Net-Zero 2050” plans, and the feedstock for SAF is a bottleneck for long-term availability (as Josef Kallo also noted).

Kerr highlighted the large internal volume of BWB aircraft, versus the traditional tube and wing configuration, allows the large hydrogen tanks to become part of the lifting body, with the tanks individually routed to each engine for redundancy. Key challenges emphasized include the need for lighter, stronger and more insulative tanks, and reliability improvements for pipes, valves and pumps below the boiling point of hydrogen, 20°K (-253°C or -423 F). Ground handling and refueling infrastructure adoption at airports and certification clarity are also necessary. Although JetZero’s S4 will use jet engines, hydrogen combustion engine designs with cryogenic cooling could allow for higher efficiency, as well as material longevity and reliability will be required. Kerr gave some insight into their conceptual hydrogen aircraft and indicated that in order to achieve the range required, they were planning for up to 15 t of liquid hydrogen onboard.

Finally, Jos Buitenhuis, Project Manager for Zero Emission Aviation at KLM Royal Dutch Airlines, presented “KLM’s Journey to Zero Emission Aviation.” The company set up advisory boards with leading hydrogen- and electric-aircraft developers and partnerships with research institutes in the Netherlands. Last year, KLM announced that it is planning a hydrogen demonstration in 2026 using ZeroAvia’s ZA2000 fuel cell, liquid hydrogen with electric motors on an ATR 72-sized regional turboprop.

Buitenhuis reviewed the potential of battery-electric and hybrid-electric aircraft toward meeting KLM’s objective to “make Zero Emission Aviation a reality.” Electric VTOL and regional aircraft can be converted to hydrogen fuel cell power, while single- and twin-aisle airliners would be appropriate for hydrogen combustion engines (which although they do not produce carbon emissions, they do produce NOx).

To closeout the conference, Buitenhuis indicated a compelling business case for hydrogen aviation in Europe. There, due to the requirements of many businesses to reduce their carbon emissions, train rides are starting to replace short-duration flights (e.g., between the Netherlands and Germany). Because of the significant increase in demand, trips can cost €500–700 (USD$570ؘ–800). KLM sees this as a real market entry opportunity for hydrogen aviation to potentially assist in lowering their company emissions while offering a competitive solution to the business market at a profit.

Wrap Up
Schneider wrapped up the meeting by summarizing the breakthroughs of the symposium and challenged the members to participate in naming top priorities in 2026. He thanked the attendees for sharing the vision to decarbonize aviation and airports with hydrogen innovations. In the conference, there was indeed a “village,” and many of the participants were either demonstrating or planning hydrogen-powered aircraft around the world. Meanwhile, significant advances in fuel cells, storage and other critical technologies are happening, while certification readiness level is moving forward with coordination between the FAA, CAA and EASA. In conjunction with this, SDOs like SAE are developing the necessary standards and safety practices to be a basis for aerospace certification input. Finally, multiple studies were presented by industry, academia and government on the concepts of operations, the hydrogen demand at airports, testing facilities and more.

At each annual H2-Aero Symposium, participants have collaborated on creating an action list for advancing hydrogen aviation, which has previously resulted in whitepapers and worldwide standardization efforts. Schneider asked, “How can we collaborate” on future efforts to advance hydrogen aviation and the attendees compiled a list of action items for the coming year.

2025 H2-Aero Symposium Action List:

• Set up a formal meeting with the FAA, the SAE hydrogen committees and industry to develop a common agreement regarding the “equivalent level of safety” for hydrogen storage and hydrogen fueling.
• Provide a focused message to DOE as a report-out from industry with hydrogen as an ideal case for aviation.
• Standardize terminology with SAE, such as fuel cell power rating, etc. with SAE AE-7F and AE-5H.
• Spread the word. Provide messaging to the public regarding the progress of hydrogen in aviation.
• Develop sharing experience forum with government (e.g., NREL), including lessons learned and data with reports.
• Develop a roadmap for hydrogen airports, sharing hydrogen aircraft demonstrations and locations.
• Determine a common hydrogen storage and fueling demonstration together with SAE, industry and government. Target fast fueling, high gravimetric density and a similar safety distance of 10 ft (3m).

Special Thanks
The VFS conference organizers and the chair wanted to thank the hard work of the volunteers who planned and organized the event, as well as the speakers. The financial support of the sponsors and exhibitors was essential to keeping the attendee costs down to allow as many participants as possible.

This year’s H2-Aero Symposium was generously sponsored by platinum sponsors Joby Aviation, Piasecki and United Therapeutics, as well as gold sponsors GTL, PowerCell and SAE International. Exhibitors included JHG Industries, M4 Engineering, Otter Stone, PowerCell and Quantum Motors.

The presentation slides are available for purchase in the VFS Library, and video recordings were also made. See www.vtol.org/h2symposium for more information.

About the Authors
Mike Hirschberg is the former VFS Executive Director (2011–2023). Jesse Schneider is the CEO/CTO of ZEV Station, and the founding chair of the SAE International AE-5H Hydrogen Aerospace Committee.