Hydrogen technologies and a hybridised narrowbody engine are likely to be included in Clean Aviation’s next call for proposals, due to be released in early 2026, although whether flight testing will be required remains up for debate.

As yet, the budget for the next call, the EU-funded body’s fourth, and the number of topics to be addressed, have yet to be agreed, says Sebastien Dubois, Clean Aviation head of unit, programme development and communications. 

However, the total budget for the project’s second phase is €900 million ($1.04 billion) spread across three calls, with call 3 accounting for €378 million.

Dubois says the exact composition of the call should be finalised by the end of November or early December, ahead of its issue in February; bidders will have three months in which to respond.

In the meantime, Clean Aviation’s governing board in September approved the launch of the 12 projects (see below) selected under its call 3, for which grants are now under preparation, allowing work to begin at the start of 2026.

These dozen projects include significant funding for flight tests of the RISE open-fan engine being developed by GE Aerospace-Safran joint venture CFM International and ground tests and preparation for flight tests of the Rolls-Royce UltraFan 30 – a narrowbody-sized version of the engine maker’s geared-fan demonstrator.

The goal is to raise the unducted fan engine to technology readiness level (TRL) 6 and the UltraFan 30 to TRL5 by 2030.

Dubois says the topics addressed in call 3 were about “harvesting the technologies that are sufficiently mature” to progress, in other words those at TRL4.

Essentially, they build on work performed in the very first call – projects that started in 2023 that will wrap up next year.

“This was the key factor to decide whether or not we are ready to proceed in call 3 – you need to be sufficiently well advanced and have already met TRL4 at project start,” says Dubois.

The relative lack of maturity of hydrogen propulsion systems – whether using fuel cells or direct combustion – is the reason for the lack of any hydrogen-related projects in the latest call, he says.

“We considered that from hydrogen domain we are not ready to go and proceed in activities on call 3.”

While that may be the case, there is also a sense that Clean Aviation’s decision was in no small measure influenced by Airbus having pushed back its expected timeline for a hydrogen-powered aircraft by up to a decade.

Dubois disagrees, however: “This was not the case: we found out in February this year once call 3 was launched when Airbus made the announcement. We had to adapt but this is not the reason there were no hydrogen topics [in call 3],” he says.

What it does mean though is that hydrogen is likely to make a resurgence in call 4, with the topic potentially accounting for around €100 million of EU investment.

The “second big chunk” of investment will be focused on hybridisation of ducted or unducted fan engines for narrowbody jets, says Dubois.

While this is likely to continue work conducted under the phase one SWITCH project led by MTU Aero Engines, it could also benefit Rolls Royce and Safran – and by extension CFM too – with a hybrid element included in both their future powerplant designs.

“This is also something we have in mind: we would like to open that parallel route for applications in the unducted or ducted fan,” says Dubois.

However, taking any such system to flight test will depend “first of all, on progress, on results, and on the timely delivery of inputs to carry this out before 2030”.

If required. flight tests will likely take place aboard an A380 that is being modified by Airbus under a separate Clean Aviation phase 1, call 2 project called COMPANION, which finishes in 2026.

Although only the CFM RISE is currently guaranteed Clean Aviation funding for flight testing – through a Safran-led call 3 project called TAKE OFF – Maria Calvo, head of unit project management, says the focus on a single engine to date is broadly down to testbed capacity and timing.

“We are aiming to assess TRL6 for several technologies within a programme [Clean Aviation] that finishes in 2030 and priorities need to be set in agreement with our members,” she says.

Other topics to be covered in call 4 are likely to include avionics improvements and industrialisation of an advanced rear fuselage design for a narrowbody jet – what Clean Aviation refers to as SMR, or short-to-medium-range aircraft – plus activities on the wing and airframe for a future hybrid-electric regional turboprop.

Additionally, call 4 will address aircraft concept and integration studies “in the field of hydrogen”, alongside other issues such as certification and market acceptance and operational considerations for next-generation technologies.

The picture for the regional aircraft space is also complex. A trio of projects was selected in call 3 – development of a multi-megawatt-class hybrid-electric engine, on-board systems including an 800V DC distribution network, and overall integration of the powertrain onto an ATR testbed – focused on TRL6 demonstration of a 20% fuel-burn saving from the propulsion system.

Clean Aviation’s overall goal for a next-generation regional turboprop is for a 30% efficiency gain, with the remaining 10% to come from improvements to the wing and fuselage. Unsurprisingly, these topics will be addressed in call 4 as part of a wider focus on what it calls the ultra-efficient regional aircraft (UERA).

Given the involvement as project leads of ATR on the airframe and Pratt & Whitney Canada on the engine you would be right in thinking that the push is towards maturing the technologies for a next-generation ATR, essentially the airframer’s ongoing Evo development, to enter service in 2035.

This is a shift from the programme’s early days when the phase one projects for regional aircraft reflected a “different, maybe more ambitious” goal for the 2035 timeframe, says Calvo.

The change in focus has been shaped by the 2024 revision of Clean Aviation’s Strategic Research & Innovation Agenda – its underlying priorities – which calls for a hybrid-electric approach in the short-term followed by “more disruptive technologies for the regional segment” from 2050.

Also retained and expanded in call 4 will be the ‘fast-track areas’, a workstream that debuted in call 3. These smaller projects – of around €5 million each – can be considered as an “innovation hub to accelerate the introduction of disruptive technologies”, says Dubois.

“Since we are very impact-driven with very large-scale projects, we need to leave room for the potential development of innovative disruptive ideas which have the potential to complement the programme objectives and the flight demonstrators,” he adds.

For instance, topics covered in call 3 include the development of new lightweight battery technology and hydrogen storage, which could both benefit future aircraft concepts but which are “not on the critical path”.

A secondary benefit is “widening the ecosystem and also to attract all necessary talents” including those from academia, research organisations and SMEs, Dubois adds.

While €20 million was allocated in call 3, the amount available for fast-track topics in each of calls 4 and 5 will rise to €40 million.

“It’s a very new and successful mechanism that will be amplified in the near future,” he says.

Calvo says the stream offers a “parallel maturation path” for technologies linked to the larger-scale projects. The involvement of an end-user is critical, she argues, as that provides the “top-level requirements [to ensure] that these can fit the needs of the larger-scale projects”.