Start your engines
To passengers, they are the familiar rumble powering aircraft across the skies. For aircraft operators, engines are a critical component in a variety of metrics such as safety, operational and economic performance, and environmental efficiency.
To improve these characteristics, airframers are working closely with numerous stakeholders to develop cutting-edge propulsion technologies that will power the next generation of aircraft. These include open fan, hydrogen, electric and hybrid-electric propulsion systems, all of which aim to achieve increased performance (i.e. in efficiency, load, range, energy consumption), and reduced climate impact, such as through reduced emissions, noise footprint, contrails etc.
Additionally, durability, reliability and safety of equipment will continue to play a large role, as will lifecycle considerations such as maintenance, repair and overhaul requirements.
The consequences of not meeting these is being felt publicly at the moment, with Airbus CEO Guillaume Faury acknowledging the company was “facing significant Pratt & Whitney engine shortages.”
Presenting Full-Year (FY) 2025 financial results, Faury said of the A320 Family, that “Pratt & Whitney’s failure to commit to the number of engines ordered by Airbus is negatively impacting this year’s guidance and the ramp-up trajectory.”
The issue lies with the recall of Pratt & Whitney’s (P&W) PW1000G geared turbofan engine, which came about following the discovery of a powder metal contamination affecting high-pressure turbine (HPT) and high-pressure compressor (HPC) components manufactured between the fourth quarter of 2015 and the third quarter of 2021. This led to mandatory inspection and replacement requirements – up to 800 GTF engines as of 2026 have been affected.
The timeline for completing these removals has pushed back with forecasts now projecting full recovery in 2027 or later. The primary driver behind this delay is an increase in shop visit turnaround times. This was initially projected to last 60 days, but has spiralled to 300–360 days per engine.
Several airlines, as well as Airbus, have sought or are pursuing financial compensation from Pratt and Whitney for the disruption caused by the issue. This includes ITA Airways, which reported grounding 28% of its fleet in November 2025 due to the ongoing global recall.
The stakes for next generation engine technology are therefore high.
Iteration or innovation?
MTU Aero Engines says it is pursuing a clear course: cleaner, quieter, more economical. According to a spokesperson, with its Claire (Clean Air Engine) technology agenda, it lays out innovative concepts for sustainable commercial aircraft engines.
“To do so, we take a two-pronged approach: one is evolutionary development of the gas turbine based on the geared turbofan (GTF), and the other is the development of completely new, revolutionary propulsion technologies, such as the Revolutionary Turbofan and the Flying Fuel Cell (FFC),” they say.
Sustainable aviation fuels and hydrogen play a key role, and the company is already working on an liquid-hydrogen fuel system for the FFC, while also building two state-of-the-art test stands for it on its premises in Munich.
“We have teams working on the engineering development of such concepts, as well as specialists in material sciences, new part and component designs, innovative production technologies, testing and MRO to ensure all the above-mentioned needs are met and reliable technological development achieved,” the spokesperson tells Aerospace Innovations.
Rather than develop a new powerplant, Pratt & Whitney is hoping to banish its woes by furthering the evolution of its GTF engine with the GTF Advantage.
According to the company, over 2,700 GTF-powered aircraft have been delivered to more than 90 customers worldwide to date, with demand for the GTF remaining strong, with over 13,000 engine orders and commitments in total across all platforms.
For Rick Deurloo, president of Commercial Engines at Pratt & Whitney, “the GTF engine delivers the lowest fuel consumption for single-aisle aircraft.”
Quoted in a recent press release, Deurloo stated that, “The GTF Advantage engine extends that lead—offering up to double the time on wing and enhancing aircraft capability—providing even greater value to operators of A320neo family aircraft.”
Pratt & Whitney claims the GTF Advantage will deliver 4-8% more take-off thrust, enabling higher payload and longer range, unlocking new destinations for airlines. As the manufacturer explains, fully intermixable and interchangeable with today’s GTF engine model, GTF Advantage will become the production standard, with full cutover expected in 2028.
In addition, customers operating the current GTF engine model will have the opportunity to realise up to 90-95% of the GTF Advantage’s durability benefits with the GTF Hot Section Plus (HS+) upgrade option for the PW1100G-JM engine, available later this year for incorporation during maintenance visits. HS+ includes only about 35 part-numbers.
Advantageous designs
The GTF Advantage features the most state-of-the-art hot section in the single-aisle market. During GTF Advantage development, MTU supported its partners by utilising fleet experience and advanced design and measurement methods to systematically increase the engine’s robustness and efficiency further. It also contributed a significantly improved design for the high-pressure compressor blades combined with an optimised protective coating for use in demanding environmental conditions. MTU’s unique compressor test facility in Munich enabled an early validation of the new high-pressure compressor’s aerodynamics. Additionally, the high-speed low-pressure turbine received an optimised active clearance control system achieving even higher efficiency.
The high-pressure turbine (HPT) and combustor also feature optimised cooling hole size, shape and location, with improved hole drilling techniques to reduce oxidation.
MTU contributes the high-speed low-pressure turbine to the GTF, one of its key components. It is also responsible for the forward four stages and Pratt & Whitney for stages five to eight. The innovative compressor is a 100% blisk construction. Blisks (blade integrated disks) are a high-tech rotor design in which the disk and blades are produced as a single piece, eliminating the need for blade roots and disk slots. This lowers weight. MTU also manufactures brush seals and integrally bladed rotors made of nickel for high-pressure compressor components beyond its design responsibility. MTU’s total program workshare in the GTF is up to 18%.
MTU is also responsible for a third of all PW1100G-JM engine assemblies and will assemble GTFA engines in future too.
For the second generation GTF, IAE International Aero Engines (IAE), a multinational consortium comprised of Japanese Aero Engines Corporation (JAEC), is investing in a range of technologies including advanced materials, cutting edge aerodynamics enabled by high-performance computing, a small high-speed core and hybrid-electric propulsion to enable required levels of performance.
The GTF Advantage engine has received type certification by both the US Federal Aviation Administration (FAA) and European Aviation Safety Agency (EASA) EASA validated the engine’s type certification, with the latter recently certifying the engine for the A320 neo family aircraft.
The goal of the second generation GTF is to further reduce the fan pressure ratio, thereby increasing the bypass ratio. The thermal efficiency of the core engine can also be further improved through approaches such as integrating the design of compressor and turbine components. This forms the first stage of MTU’s new version of Claire– which follows the first iteration, released in 2007.
The goal of the second step, to be completed by 2035, is to have not only the next-generation GTF, but also a Water-Enhanced Turbofan (WET)– driven by SAFs or hydrogen – ready to use in all thrust categories, along with the Flying Fuel Cell for shorter, regional flights. A GTF powered by hydrogen is also conceivable during this phase.
Part of the Sustainable Water-Injecting Turbofan Comprising Hybrid-Electrics (SWITCH) project, and using a hybrid-electric GTF powertrain, the WET concept recovers water vapor from the engine exhaust and re-injects it into the combustion chamber to significantly improve fuel efficiency, reduce NOx emissions, and lessen contrail forming emissions.
Led by MTU Aero Engines, SWITCH has the participating support of Airbus, Pratt & Whitney, Collins Aerospace and GKN Aerospace.
2050 marks the third Claire stage. Here, MTU’s goal is to further improve overall efficiency both for the GTF and for the WET engine. MTU says that near drop-in fuels – SAFs with chemical adjustments – can be used to achieve maximum reductions in climate impact. If the WET engine is operated with hydrogen, this would not only have further advantages with regards to climate-related emissions, but they claim would additionally have the potential to reduce weight and the air resistance of the engine thanks to more-compact design and construction.
Only Fans
Another project under the auspices of the European Union’s Clean Aviation Joint Undertaking is TAKE OFF (Technology And Knowledge for European Open Fan Flight), which aims bring the first Open Fan engine to flight before the end of the decade.
The Open Fan engine architecture was first presented in 2021 as part of the CFM RISE technology demonstration programme, which seeks to develop propulsion technologies capable of delivering significantly improved environmental performance. The concept is designed to achieve approximately 20% greater fuel efficiency compared with current engine technologies for the next generation of aircraft expected to enter service in the mid-2030s.
As the consortium leader, Safran Aircraft Engines will coordinate collaboration among leading aerospace companies, universities and research institutions. The project includes participation from major industrial partners such as Airbus, Avio Aero and GKN Aerospace, alongside academic and research organisations contributing to technological development across multiple disciplines.
TAKE OFF builds on the Clean Aviation OFELIA (Open Fan for Environmental Low Impact of Aviation) project, which aims to demonstrate at Technology Readiness Level 5 (TRL5) the RISE Open Fan architecture, for the small-medium range (SMR) aircraft to achieve or surpass the Air Transport Action Group’s goals on the way towards carbon neutrality by 2050.
The engine is key in this effort and Clean Aviation believes that the Open Fan engine architecture is the most promising solution in terms of fuel efficiency to both achieve environmental goals (20% emissions reduction versus 2020) and target a rapid Entry into Service, as early as 2035.
To this end, OFELIA will focus on the high TRL full scale demonstration of the engine architecture and on the development of key enablers for the Open Fan. OFELIA will allow installation of an increased fan diameter on a conventional aircraft configuration, thanks to innovative turbomachinery technical solutions. Following the architecture definition, this project will perform a large-scale Open Fan engine ground test campaign, deliver flightworthy propulsive system definition, and prepare an in-flight demonstration, planned for an Airbus A380, for the phase 2 of Clean Aviation, As María Calvo, Head of Unit Project Management at Clean Aviation has remarked, “TAKE OFF must now demonstrate the viability of the disruptive Open Fan engine concept at a higher maturity level, in line with the flight test campaign expected for 2029.”
All RISE
Launched in 2021, the CFM RISE program aims to improve fuel efficiency by more than 20% compared with current engines, by combining disruptive technologies with the development of an Open Fan architecture that removes the traditional casing, allowing for a larger fan size with less drag RISE will use adaptive engine technologies, also known as variable bypass architecture, to boost performance while allowing safe and efficient operation at every stage of a flight.
The project is -engineering a lightweight compact core, which houses the compression and combustion modules, to be smaller and optimize thermal efficiency, with an advanced cooling system and materials that can withstand extremely high temperatures. The core is being designed for compatibility with next-generation fuels, including unblended sustainable aviation fuel (SAF) and hydrogen, as well as with hybrid electric systems for the next generation of commercial narrow-body aircraft.
The pace of the programme is impressive. It has already seen over 350 component and module tests completed to date, including major tests conducted by Safran on the low-pressure turbine and compressor, bearing systems and equipment for the new pitch control functions of the Open Fan.
Safran has also recently tested three fan blade configurations as part of a demonstration of the mechanical integrity of the components in an unducted architecture and to validate improvements in aerodynamic and acoustic performance. The fan blades, which are over 1.6 meter in length, underwent over 175 ingestion and endurance tests at the test facilities at Safran’s Villaroche center, which were specially configured to accommodate large-scale components, in addition to the 300 hours of wind tunnel tests on a scaled-down Open Fan model at ONERA (France) and DNW (Netherlands), in partnership with Airbus.
Further collaboration has been agreed as the Civil Aviation Authority of Singapore (CAAS) and Airbus seek to study the impact of Open Fan and other RISE program technologies on airport operations to develop a comprehensive readiness framework that serves as the global blueprint for airframers, airports, and airlines worldwide.
Under an MOU, the parties will co-develop a comprehensive readiness framework to integrate Open Fan engines for the next generations of aircraft, into existing airport operations, including aircraft system and design considerations, infrastructure modifications if any, operational procedure changes, safety standards, and regulatory procedures. They also plan to conduct operational trials of the RISE programme’s Open Fan engine demonstrators at Singapore Changi Airport or Seletar Airport to test and validate the readiness framework and assess operational feasibility of this new technology.
The Ultra way
In the UK, Rolls-Royce is advancing the UltraFan which it unveiled publicly in 2014. As the firm explains, UltraFan is a fundamentally different design architecture to that within the approximately 4,200 Rolls-Royce Civil large engines currently in service, as it incorporates a geared design that no other industry player has produced at this size before – at one square metre it can produce over 50MW – enough to power 500 family cars.
The planetary design of the power gearbox is designed to allow the turbine at the rear of the engine to run at a very high speed while the fan at the front runs at a slower speed.
The widebody variant, Ultrafan 80, aims to deliver 25% more fuel efficiency than first generation Trent – the Trent 700, and 10% more fuel efficiency than the Trent XWB, which is seen as the most efficient aero-engine in service.
The first phase of testing took place in 2023 at Rolls Royce’s £90 million purpose-built facility – Test Bed 80 – in Derby using 100% sustainable aviation fuel. Following forensic strip and inspection, a second build of the UltraFan 80 demonstrator has been defined with further testing planned later in 2026.
Rolls Royce has recently been confirmed as the lead of the UNIFIED – Ultra Novel and Innovative Fully Integrated Engine Demonstrations – consortium. Backed by €64million funding, the project will focus on maturing and advancing next-generation propulsion technologies for future narrowbody applications, supporting planned ground testing of the UltraFan 30 demonstrator in 2028 and helping establish a credible pathway toward future flight test.
With the UltraFan 30 demonstrator, Rolls Royce says it is committed to providing a ducted geared solution for the narrowbody segment in partnership. The demonstrator is targeting 20% fuel burn improvement relative to the current in-service engines.
Issuing a fact sheet, the company says the “UltraFan 30 demonstrator takes what we’ve learnt in creating world leading widebody and business aviation engines to the narrowbody market, using technology from proven and safe architectures.”
Features include the same architecture and technology as found within the Ultra80 demonstrator, namely new engine core architecture to deliver maximum fuel burn efficiency and reduce emissions; advanced manufacturing, materials and technologies such as Additive Layered Manufacturing (ALM) to save on waste and allow for more intricate designs and CMC materials to withstand higher temperatures, and a geared design which will deliver efficient power for the high-thrust, high-bypass ratio engines of the future (although not on the same scale as Utrafan 80).
Also featured is Carbon-Titanium (CTi) composite fan system and a composite casing developed by the University of Bristol.
While carbon-fibre reinforced composites have many useful properties for aerospace applications, particularly in terms of reducing weight and fuel consumption, such laminated structures can be susceptible to delamination of the fibre-reinforced layers under impact.
To achieve a commercially viable composite fan system solution, Rolls-Royce›s development has drawn on two key research areas facilitated by the ongoing partnership with the University. The first was a new approach to numerical modelling that can predict the occurrence of delamination and ensure that designs mitigate the effects of delamination damage under various impact loads.
The second development was a new Direct Insertion manufacturing method for through-thickness reinforcement (TTR) of the fan blades, achieved by inserting pre-cured carbon fibre rods into the composite laminate. This enables the reinforcement of thick laminates with far higher accuracy and fewer process-induced defects than any other existing means. TTR is essential for managing any potential impact damage. Following the invention of the Direct Insertion method at the University of Bristol, the technology was scaled up at the National Composites Centre, before being implemented by Rolls-Royce at their Composites Technology Facility in Filton.
The aviation industry is moving forward with a shared ambition to make aviation more sustainable. Projects such as those covered above are helping to shape the sector’s future, showcasing the competitive benefits of architecture in terms of energy efficiency and acoustic performances.
By Alex Preston
