ZeroAvia, the Hydrogen-Electric Drivetrain Going Into the Dornier Two Twenty-Eight, and What Fuel Cell Propulsion Actually Demands Before a Regional Turboprop Burns Its Last Gallon of Jet-A

In January 2023, ZeroAvia flew a modified Dornier 228 out of Cotswold Airport in the United Kingdom with one turboprop replaced by a hydrogen-electric powertrain. The only exhaust product was water vapor. That flight represents the leading edge of a propulsion transition that could fundamentally change what regional aviation looks and smells like - but the path from demonstrator to revenue service is long, and the honest obstacles deserve as much attention as the milestone.

What Is ZeroAvia’s Hydrogen-Electric Powertrain?

ZeroAvia, founded in 2018 with offices in the United Kingdom and California, is building a propulsion system that generates electricity from hydrogen through a fuel cell, then uses that electricity to drive motors turning conventional propellers. No combustion. No carbon dioxide. No nitrogen oxides. The only byproduct is water.

The company’s near-term commercial product is the ZA600, a 600-kilowatt powertrain designed as a direct replacement for the Honeywell TPE331 turboprops on the Dornier 228. Those engines produce approximately 575 shaft horsepower each - the ZA600 has the power margin to substitute cleanly on both nacelles.

Hydrogen Combustion vs. Fuel Cell: Why the Distinction Matters

“Hydrogen aircraft” actually describes two fundamentally different technologies, and conflating them leads to real confusion about what ZeroAvia is building.

The first approach burns hydrogen directly in a gas turbine or piston engine - the same thermodynamic process as conventional propulsion, just with a different molecule. Rolls-Royce and Airbus have explored this route. It produces enormous power, but high-temperature combustion still generates nitrogen oxides. Those NOx emissions interact with atmospheric chemistry at altitude in ways researchers are still modeling, and water-rich exhaust adds contrail effects that complicate the full emissions picture.

ZeroAvia is doing something categorically different. Inside a proton exchange membrane fuel cell, hydrogen molecules enter one side, ambient oxygen enters the other, and the electrochemical reaction produces electrons - electrical current - and water. That is the complete exhaust product. This is a genuinely different category of clean from anything that involves a combustion cycle.

Why the Dornier 228 Is the Right Test Airframe

The Dornier 228 is a high-wing, twin-turboprop regional aircraft carrying up to 19 passengers, certified in the early 1980s and operated on regional routes worldwide for over four decades. It is structurally well-understood, with a maintenance record filling rooms of data.

When certifying a completely novel propulsion concept, that matters enormously. Every variable except the propulsion system is a known quantity - which means anomalies in test data point directly at the powertrain rather than getting lost in structural or aerodynamic unknowns.

The January 2023 flight at Cotswold was not a certification event. One turboprop remained conventional; the hydrogen-electric powertrain occupied the port nacelle, with the fuel cell stack sitting in the cabin. Twenty minutes of flight through full test profiles. That may sound modest. It isn’t. It confirms that the electrochemical stack, power management electronics, motor and gearbox integration, and hydrogen storage system all function together in a moving airframe at altitude - converting a ground test program into actual flight data.

ZeroAvia has since been working toward a full dual-installation demonstrator with hydrogen-electric powertrains on both nacelles simultaneously, the configuration that actually models the operational product.

The Physics of Hydrogen as Aviation Fuel

Hydrogen carries approximately 120 megajoules per kilogram of energy. Jet-A carries about 43 megajoules per kilogram. On a pure mass basis, hydrogen stores nearly three times the energy of conventional jet fuel - a compelling advantage for aircraft that pay a heavy penalty for heavy fuel.

The story changes when you measure by volume.

Liquid hydrogen must be stored at minus 253 degrees Celsius - four degrees above absolute zero. At that temperature, one liter of liquid hydrogen holds approximately 70 grams of usable fuel. One liter of jet-A holds approximately 800 grams. On a volume basis, liquid hydrogen stores roughly eleven times less energy per liter than conventional fuel. The aircraft carries lighter fuel, but in tanks that must be significantly larger.

A retrofit into an existing airframe like the Dornier 228 isn’t just a powertrain swap. It potentially involves structural modifications to accommodate tanks designed for a cryogenic fluid, not the dense liquid that fit inside conventional wing tanks.

Compressed vs. Liquid Hydrogen: The Storage Trade-Off

ZeroAvia’s current flight test program uses compressed gaseous hydrogen rather than liquid hydrogen - carbon fiber composite cylinders at pressures between 350 and 700 bar. This sidesteps the cryogenic engineering challenge for now, but it makes the volumetric situation worse. Compressed gaseous hydrogen has lower energy density by volume than liquid hydrogen. The tanks are heavy per unit of energy stored, large, and consume cabin or cargo volume.

For short regional routes, this is an acceptable trade. Legs of 150 to 250 nautical miles don’t require the fuel load of a narrowbody flying transatlantic. If a hydrogen-electric Dornier 228 can carry 11 to 13 passengers 200 nautical miles with acceptable economics, the operational case works for a meaningful portion of the regional network. This technology is not walking up to a seven-hour hub route and solving it. The range limitations are real, and they’re baked into the physics.

Who Is Backing ZeroAvia - and Why It Matters

Alaska Air Group, which owns Horizon Air, has signed a letter of intent for up to 76 ZeroAvia-powered aircraft. Horizon Air operates the Dornier 228 today on routes in the Pacific Northwest and Alaska. This is not a logo on a press release - it is an airline that runs those specific aircraft on specific routes, pays to maintain them, and wants early access to whatever propulsion comes next.

International Airlines Group (parent of British Airways) and Deutsche Lufthansa Group are also committed. These are operators who understand what regional propulsion costs to run and what carbon accounting pressure from investors and regulators looks like on their networks.

ZeroAvia has raised over $100 million to date and continues to operate.

Why Hydrogen Infrastructure May Be the Harder Problem

When a hydrogen-electric aircraft lands, it needs hydrogen on the ramp. That infrastructure does not exist at regional airports in North America or Europe today. Industrial hydrogen distribution exists for manufacturing and chemical processing - it is not configured for aircraft refueling speeds or airport ramp logistics.

Building ramp hydrogen capability requires an airport authority to work with a hydrogen supplier, construct appropriate storage, build the safety envelope, train ramp personnel, and obtain regulatory approval for a novel fueling operation. That process plays out airport by airport, route by route.

Compare that to sustainable aviation fuel (SAF), which pumps through the same trucks, the same hydrant systems, into the same airframe fuel systems that exist today. SAF still produces CO₂ when burned, but on a lifecycle basis approximately 80 percent less than conventional jet fuel depending on feedstock and production method. SAF gets most of the way to carbon neutral but not to zero. Hydrogen-electric gets closer to zero but requires building an entirely new fuel supply chain at every airport where the aircraft will operate.

These are not competing technologies so much as tools for different parts of the same decarbonization problem. SAF works in the fleet today. Hydrogen is the longer-horizon play that demands far more infrastructure investment and time to execute.

The Universal Hydrogen Cautionary Example

Universal Hydrogen was pursuing a parallel path - converting an ATR 42 regional turboprop to hydrogen-electric propulsion using modular fuel capsules swappable at the airport like cargo containers, a clever solution to the infrastructure problem.

They flew a demonstrator in March 2023. The technology worked. And in May 2023, Universal Hydrogen ran out of money and shut down.

The capital required to move from a working demonstrator to a type-certificated, commercially available, revenue-service propulsion system is substantial - hundreds of millions of dollars, likely more. The timeline from demonstrator flight to certified product is measured in years, not quarters. Universal Hydrogen could not raise what it needed as venture capital interest in deep-tech aerospace cooled. ZeroAvia continues to operate, but the outcome is a clear reminder that aviation technology timelines are measured in decades, and startups operating on that timescale face capital structure challenges that established manufacturers simply don’t face.

Where Certification Actually Stands

Both the FAA and EASA have been engaging with ZeroAvia and the broader hydrogen aviation ecosystem. The honest state of play: the certification framework for hydrogen-electric powertrains in commercial aviation does not fully exist yet. It needs to be built.

Existing turbine and piston certification pathways address combustion engines with known failure modes, known fuel system behaviors, and decades of service history. A fuel cell powertrain has different failure modes, different maintenance intervals, different ground handling requirements, and different fire protection considerations. What are the structural and safety requirements for cryogenic hydrogen tanks in a pressurized fuselage? How do you establish initial airworthiness standards for a technology category that has never been certificated before?

Both agencies have signaled willingness to work collaboratively with hydrogen propulsion developers rather than waiting for them to arrive with a finished aircraft. That’s a healthier posture than these agencies historically took with novel concepts. But collaborative engagement does not compress the actual engineering work. The testing still has to happen, and the data still has to exist before the approval can follow.

ZeroAvia’s stated target is initial entry into service for the ZA600 in certified 19-seat aircraft in the second half of this decade. Given the Universal Hydrogen experience, the certification unknowns, and the infrastructure gap that still needs closing, the realistic probability-weighted expectation lands somewhere closer to the early to mid-2030s for genuine revenue service at any meaningful scale. That is not a dismissal of the program - it is what aviation propulsion transitions look like historically.

What Comes After the ZA600

ZeroAvia’s larger roadmap item is the ZA2000 - 2 megawatts of output, sized for 40- to 80-seat aircraft: the regional jets and larger turboprops that carry more of the actual passenger load in this category. The ZA2000 is further out in the development timeline. The ZA600 is the proof of concept that validates the technology, the certification path, and the operational ecosystem that larger aircraft will inherit.

Aviation represents approximately 2 percent of global CO₂ emissions, but short regional flying contributes disproportionately on a per-seat-per-mile basis because smaller regional aircraft are less thermally efficient than the high-bypass turbofans on modern narrowbodies. If hydrogen-electric propulsion achieves entry into service in the regional category first - which is exactly what ZeroAvia is targeting - the emissions impact per aircraft replaced is proportionally significant. And the regional network is precisely where the range limitations of current hydrogen technology are least penalizing.

What Pilots and Industry Observers Should Watch

The first type certificate for a fuel cell-powered commercial aircraft will serve as the template for every hydrogen aircraft program that follows. Watch the ZeroAvia certification engagement with the FAA and EASA - the frameworks they develop now will apply to the entire category.

Watch hydrogen infrastructure investments at regional airports. The first airports to build refueling capability will be the first to see revenue service. And watch the Alaska Air/Horizon Air partnership develop - an operator that actually flies those specific aircraft on those specific routes is as close to a real-world stress test as ZeroAvia could have found before the certification finish line.

Key Takeaways

• ZeroAvia flew a hydrogen-electric Dornier 228 at Cotswold Airport in January 2023, with water vapor as the only exhaust product - a fuel cell powertrain, not hydrogen combustion.
• The ZA600 produces 600 kW, matching the power output of the Dornier 228’s existing Honeywell TPE331 turboprops, and is sized for 19-seat regional aircraft.
• Hydrogen carries nearly 3× the energy of jet-A by weight, but roughly 11× less by volume as a liquid - meaning tanks must be substantially larger, complicating retrofits.
• Airport hydrogen infrastructure does not exist at regional airports today; building it airport by airport is likely a harder problem to solve than the powertrain itself.
• Universal Hydrogen flew a successful demonstrator in March 2023 and shut down two months later - a direct warning that capital timelines and aviation certification timelines are not easily aligned.
• Realistic revenue service at meaningful scale is more likely in the early to mid-2030s than the second half of this decade, consistent with the historical pace of propulsion transitions.