This article is based on an official press release from RTX.

RTX and Pratt & Whitney Unveil Hydrogen-Steam Engine Design Developed by AI

RTX, the parent company of Pratt & Whitney, has announced the successful conclusion of a multi-year research initiative aimed at redefining hydrogen propulsion for commercial aviation. On December 9, 2025, the company revealed details of its HySIITE (Hydrogen Steam Injected, Intercooled Turbine Engine) project, which utilized a proprietary artificial intelligence tool to design an engine architecture capable of achieving a 35% improvement in energy efficiency compared to today’s state-of-the-art turbofans.

The project, supported by a $3.8 million grant from the U.S. Department of Energy’s ARPA-E program, represents a significant departure from traditional engine design. Rather than adapting existing fossil-fuel engines to burn Hydrogen, the HySIITE project sought to exploit the specific cryogenic and chemical properties of liquid hydrogen from the ground up. According to RTX, the resulting design not only boosts fuel efficiency but also eliminates over 99% of nitrogen oxide (NOx) emissions, addressing one of the primary environmental concerns associated with hydrogen combustion.

The “DISCOVER” AI Tool

The breakthrough in the HySIITE architecture was made possible by an internal RTX artificial intelligence tool named DISCOVER. Traditional engine design often relies on iterating upon proven architectures. However, to fully leverage hydrogen, engineers needed to explore a design space far too vast for human calculation alone.

According to the company, the DISCOVER tool analyzed approximately 70 different engine components and calculated an estimated 1 quattuorvigintillion ($10^{75}$) possible configurations. From this near-infinite pool of possibilities, the AI identified 4,202 feasible designs, presenting them as a scatter plot that allowed engineers to pinpoint the optimal architecture.

“Just to put that in perspective, there are $10^{80}$ atoms in the universe.”

, Larry Zeidner, RTX Technical Fellow, regarding the scale of the design space analyzed.

This computational approach allowed the team to identify a “semi-closed” thermodynamic cycle that human engineers might have missed using conventional methods. RTX notes that the DISCOVER tool is now being applied across other divisions, including Collins Aerospace and Raytheon, to optimize designs for microelectronics and power systems.

Reimagining the Thermodynamic Cycle

The selected HySIITE design differs radically from standard jet engines. While hydrogen burns hotter and faster than jet fuel, characteristics that typically lead to high NOx emissions, the new architecture turns these traits into advantages through steam injection and intercooling.

In the HySIITE engine, liquid hydrogen (stored at -253°C) is used to cool the incoming air before combustion, a process known as intercooling. Furthermore, the engine is designed to capture water vapor from its own exhaust. RTX reports that the system recovers approximately one gallon of water every three seconds. This recovered water is then injected back into the combustor as steam.

“We were really trying to reimagine, from the ground up, what a hydrogen engine could be… We found that we can take advantage of some of the unique properties of hydrogen to do things that can’t be done with jet fuel.”

, Neil Terwilliger, HySIITE Principal Investigator.

The steam injection serves a dual purpose: it increases the power output of the turbine and strictly controls the temperature of the hydrogen flame, which is the key factor in reducing NOx emissions to near-zero levels.

Future Applications and Industry Context

While the HySIITE project was a research-focused proof-of-concept, RTX is moving forward with follow-on programs to mature the technologies required for a potential entry-into-service around 2050. These initiatives include the HyADES (Hydrogen Advanced Design Engine Study) project with Pratt & Whitney Canada and the NASA AACES 2050 program, which aims to develop sustainable aircraft concepts for the mid-century timeframe.

AirPro News Analysis

The unveiling of the HySIITE architecture positions RTX as a distinct competitor in the growing hydrogen propulsion landscape. While competitors like Airbus are targeting a 2035 entry for their ZEROe hydrogen aircraft, and CFM International (GE Aerospace and Safran) is focusing on the open-fan RISE architecture, RTX appears to be playing a longer game focused on thermal efficiency maximization.

The decision to pursue a steam-injected, semi-closed cycle differentiates Pratt & Whitney from Rolls-Royce, which has focused heavily on direct hydrogen combustion for widebody applications. By prioritizing the elimination of NOx, often cited by environmental groups as a critical hurdle for hydrogen aviation, RTX is addressing the non-CO2 climate impacts of aviation that contrail-avoidance strategies alone cannot solve.

However, the timeline remains a significant factor. With a target of 2050 for this specific architecture, the industry will likely see intermediate hydrogen solutions or hybrid-electric configurations enter the market well before the HySIITE concept becomes a commercial reality.

Sources: RTX

New “Book and Claim” Model Brings Sustainable Fuel to Remote Air Ambulances

On December 10, 2025, Airbus Helicopters and the French operator SAF Hélicoptères announced a strategic partnership designed to decarbonize emergency medical services (HEMS) in Catalonia, Spain. The initiative utilizes a “Book and Claim” mechanism to supply Sustainable Aviation Fuel (SAF) credits to operations that physically cannot access the fuel, marking a significant shift in how remote aviation sectors approach environmental compliance.

The project focuses on two Airbus H145 helicopters operated by SAF Hélicoptères for the Catalan Department of Health’s Emergency Medical Services. According to the announcement, this arrangement allows the operator to reduce its carbon footprint despite the logistical impossibility of delivering physical biofuels to small, decentralized hospital helipads.

Overcoming the “Last Mile” Logistics Challenge

Emergency medical missions present a unique challenge for decarbonization. Unlike commercial airlines that refuel at major hubs with established infrastructure, HEMS helicopters often operate from remote bases or hospital rooftops. Transporting small quantities of SAF to these scattered locations by truck would be inefficient and could generate more carbon emissions than the biofuel saves.

To solve this, Airbus and SAF Hélicoptères have adopted the “Book and Claim” model. Under this system, the operator purchases SAF “certificates” representing the environmental benefits of the fuel. The physical fuel is then pumped into the aviation system at a central location, such as a major airport, where it is consumed by other aircraft. SAF Hélicoptères then claims the carbon reduction for its specific HEMS missions in Catalonia.

Jean-Louis Camus, Co-director of SAF Hélicoptères, explained the contractual necessity of this arrangement in the company’s statement:

“In my contract, I state that I will pay the equivalent of a portion of my helicopters’ fuel usage in exchange for a certificate.”

The Role of Airbus and Certification

Airbus Helicopters is acting as the market facilitator in this pilot program. According to the release, the manufacturer purchases SAF certificates in bulk from producers and resells them to smaller operators. This approach is intended to “de-risk” the process for customers who may lack the purchasing power to negotiate large fuel contracts independently.

Julien Manhes, Head of Sustainable Aviation Fuel at Airbus, highlighted the company’s objective to democratize access to green fuels:

“For a lot of smaller operators, getting access to SAF can be challenging… Airbus can simplify and derisk the process.”

To ensure transparency and prevent “double counting”, where two different parties might claim the same environmental benefit, the initiative utilizes a registry managed by the Roundtable on Sustainable Biomaterials (RSB). This certification ensures that once the carbon reduction is claimed by the HEMS operator, it cannot be claimed by the entity physically burning the fuel at the central hub.

AirPro News Analysis: The Regulatory Gap

While the “Book and Claim” model solves the immediate logistical hurdles for HEMS operators, it faces a complex regulatory landscape. As of late 2025, major frameworks like the EU Renewable Energy Directive (RED) and the ReFuelEU initiative prioritize the physical supply of fuel at mandated airports. Consequently, “Book and Claim” systems are not yet fully recognized for meeting all national compliance targets, creating a temporary regulatory gap.

Furthermore, while this system reduces Scope 3 emissions for clients like the Catalan Department of Health, the cost of SAF remains significantly higher, often 2 to 8 times that of conventional jet fuel. The willingness of public health administrations to absorb these costs signals a shift in public tenders, where environmental compliance is becoming a non-negotiable requirement for government contracts.

A Model for Future Operations

The deployment in Catalonia serves as a proof-of-concept for the wider industry. Juan Carlos Gomez Herrera, representing the Catalan Administration, noted that the initiative aligns with their broader public health mandate, viewing environmental responsibility as an extension of immediate medical care.

By decoupling the physical fuel from its environmental attributes, Airbus and SAF Hélicoptères are demonstrating a viable pathway for decarbonizing decentralized aviation sectors that have previously been left behind by airport-centric green policies.

Sources: Airbus

This article is based on an official press release from Eve Air Mobility / Embraer and supporting market data.

Eve Air Mobility Strengthens Financial Runway with B3 Listing and $40 Million BNDES Loan

Eve Air Mobility (“Eve”), the electric vertical take-off and landing (eVTOL) subsidiary of aerospace manufacturer Embraer, has executed a significant dual-strategy milestone to fortify its position in the urban air mobility sector. On December 9, 2025, the company celebrated its official listing on the Brazilian stock exchange (B3) while simultaneously announcing a fresh Investments package worth approximately $40 million (R$200 million) from Brazil’s National Development Bank (BNDES).

The new capital injection, sourced primarily from the BNDES Climate Fund, is earmarked for the critical development phases of Eve’s eVTOL program. According to the company’s announcement, these funds will support the integration of electric motors for the program’s first “certification-conforming” prototype and fund the rigorous test campaigns required by Brazil’s Civil Aviation Agency (ANAC). This latest development underscores the Brazilian government’s continued support for Eve as a strategic national asset in the global aerospace industry.

Strategic Financing via BNDES Climate Fund

The financing agreement, valued at R$200 million, is structured not as a standard commercial loan but as a strategic development credit designed to foster Green-Technology within Brazil. The funding is divided into two specific sub-credits, providing Eve with a 15-year maturity term that offers a long-term financial runway.

According to details released regarding the transaction, the financing is split as follows:

• Sub-credit A (~$32 million): Sourced from the Fundo Clima (Climate Fund) under the “Green Industry” modality. This capital is specifically allocated for projects that reduce greenhouse gas emissions and promote sustainable urban development.
• Sub-credit B (~$8 million): Sourced from the FINEM Innovation Line, utilizing BNDES resources raised in foreign currency to support technological innovation.

This latest infusion brings the total support from BNDES to Eve to over $240 million since 2022. The favorable terms and long maturity period reflect the state’s commitment to ensuring Eve remains competitive against well-capitalized international rivals.

Dual Listing on the B3 Exchange

Coinciding with the funding announcement, Eve formally debuted on the B3, Brazil’s primary stock exchange, under the ticker symbol EVEB31. While the company remains legally headquartered in the United States with its primary listing on the New York Stock Exchange (NYSE: EVEX), the dual listing allows Eve to tap into a broader pool of capital.

The move enables Brazilian institutional and retail investors, who may face barriers trading on the NYSE, to invest directly in the company. This strategy reinforces Eve’s identity as a Brazilian innovator leveraging Embraer’s industrial heritage while maintaining global market access.

Program Status and Industrialization

Eve continues to leverage its relationship with Embraer, the world’s third-largest aircraft manufacturer, to advance its industrial capabilities. The company is currently finalizing its first full-scale prototype and establishing a production facility in Taubaté, São Paulo. The facility is expected to utilize Embraer’s existing supply chain ecosystem to streamline Manufacturing.

According to company data, Eve currently holds one of the industry’s largest order backlogs, comprising approximately 2,800 Letters of Intent (LOIs) valued at roughly $14 billion. The company is targeting an Entry into Service (EIS) date of 2027.

AirPro News Analysis

The global eVTOL market is currently undergoing a sharp bifurcation, separating well-capitalized leaders from struggling independent Startups. Eve’s recent moves highlight the effectiveness of its “capital-light” strategy, which relies on Embraer for R&D and infrastructure rather than building everything from scratch.

While competitors like Joby Aviation have raised massive sums, such as their recent $500 million investment from Toyota, to fund vertical integration, Eve’s $40 million loan carries significant weight due to its efficiency. By utilizing Embraer’s existing testing grounds and engineering workforce, every dollar of debt goes further for Eve than for a startup like Lilium, which recently faced insolvency.

Furthermore, the BNDES loan signals “sovereign backing.” In an industry fraught with regulatory and certification risks, the Brazilian government’s financial stake in Eve serves as a confidence signal to private investors. It suggests that Brazil views the success of Eve not just as a corporate goal, but as a matter of national industrial strategy, similar to how the U.S. and China support their respective aerospace champions.

Frequently Asked Questions

What are Eve Air Mobility’s stock tickers?
Eve is listed on the NYSE under the ticker EVEX and now on the Brazilian B3 exchange under the ticker EVEB31.

What is the value of the new BNDES financing?
The financing package is worth approximately R$200 million, or roughly $40 million USD.

When is Eve’s aircraft expected to enter service?
Eve is targeting an Entry into Service (EIS) date of 2027.

What is the BNDES Climate Fund?
The Fundo Clima is a Brazilian government financing program dedicated to projects that mitigate climate change. Eve’s participation falls under the “Green Industry” modality, supporting the development of zero-emission aviation technology.

Sources: Eve Air Mobility / Embraer Press Release, BNDES Official Data