Product stewardship

Reducing engine noise and exhaust gases

Health impact of aircraft engines

As part of our sustainable product development, we are not only working on new propulsion concepts for zero-emission aviation. Our Clean Air Engine agenda also focuses on minimizing the impact that our products—in the air and on the ground—have on people’s health. This includes reducing aircraft noise and exhaust emissions to make flying significantly quieter and cleaner.


Our new WET engine propulsion concept can significantly reduce or even eliminate pollutants. It works by injecting water into the combustor, which, based on what we know so far, can cut NOx emissions by up to 80%.

We undertake to protect the environment; climate action is one part of this, but our endeavors go much further. We are also committed to reducing aircraft noise and improving air quality through lower exhaust emissions. This is important because with quiet and clean propulsion concepts, we can improve the situation for residents living near and around airports in terms of noise abatement and air quality, thereby promoting society’s acceptance of air travel. As with our approach to climate action, we have established several pillars to anchor the issues of aircraft noise and emissions in the company. In our global Code of Conduct, we commit to environmental protection and explicitly to reducing noise and exhaust emissions from aircraft engines. We want to set standards in this area, and we have formulated our goal accordingly. The MTU Principles also include the requirement to create products with lower noise and pollutant emissions under the heading “Environment and society.”


Our contribution to SDGs 9 and 12

Our commitment to reducing aircraft noise helps achieve two SDGs of the UN’s 2030 Agenda: SDG 9 on “Industry, innovation and infrastructure” and SDG 12 on “Responsible consumption and production.” Reducing aircraft noise levels improves the aviation infrastructure that is important for growth and prosperity while at the same time leading to lower levels of pollution for people living around airports. Lower exhaust emissions help improve local air quality.

Industry, innovation and infrastructure
Responsible consumption and production

→ Learn more about our contribution to the SDGs of the UN’s 2030 Agenda

In contrast to CO2 emissions, to receive certification from aviation authorities both aircraft and engines must meet noise and emissions limits set by the International Civil Aviation Organization (ICAO); in the past, these limits for noise have been successively tightened. National aviation authorities are responsible for certification. Furthermore, at almost every airport in the world, the fees charged for takeoff and landing are dependent on the noise emissions of the aircraft model.

How is aircraft noise generated?

Aircraft noise is caused by both the engine and the aircraft itself. Noise during takeoff is largely down to the fan and engine airflow; during landing, the aircraft also adds to noise as a result of turbulence around the fuselage, wings and landing gear. Noise is also produced by the aerodynamic interaction between components. The core engine accounts for a relatively small proportion of aircraft noise.

In the certification of new aircraft models, noise is measured using a standardized process at three defined points and then cumulated. Aircraft noise has decreased continuously since the 1960s, by a total of about 17 EPNdB (effective perceived noise decibels; a specific unit for measuring the relative noisiness of aircraft) or about 70%.


Quieter flying: Our Clean Air Engine agenda provides answers in this area, too.

With our Clean Air Engine agenda (Claire), we are pursuing not only climate action targets → Climate impact of aircraft engines, but also targets for reducing aircraft noise emissions. Our project is in line with the European aviation industry and research sector’s Strategic Research and Innovation Agenda (SRIA), which calls for noise reductions of 55% by 2035 and 65% by 2050. With the first-generation geared turbofan, which we develop and manufacture together with our partner Pratt & Whitney, we have already significantly reduced aircraft noise emissions as part of Claire Stage 1. They are on average 15–20 EPNdB (cumulated over the three ICAO measuring points) below the current legally stipulated noise emission class, ICAO Stage 4. This equates to a reduction in the geared turbofan’s noise footprint (spread of aircraft noise near airports) of 75%.

less aircraft noise

Noise abatement plays an important role in our activities: With our Clean Air Engine agenda, we have set ourselves staggered targets for reducing aircraft noise levels—by up to 65% by 2050. Our models are already well below the legal limit.

In the next step, Claire Stage 2, improvements to the second-generation geared turbofan are set to reduce aircraft and engine noise emissions by 50% (base year 2000). To achieve this, the engine industry has developed the necessary fans with a low pressure ratio and low-noise low-pressure turbines as part of European research programs such as ENOVAL. Entry into  service is scheduled for later this decade.

SRIA and Claire agenda targets for reducing noise emissions


All the targets refer to an aircraft’s noise emissions including engines (improvements are relative to an aircraft from the year 2000); noise level in EPNdB (effective perceived noise decibels) are relative to the limits defined by the International Civil Aviation Organization (ICAO) (Stage 4). A reduction in noise emissions of 10 EPNdB corresponds to a 50% cut in perceived noise.

In the third and final stage of Claire, noise emissions are set to be reduced by as much as 65% (base year 2000) thanks to new engine architectures. Our engineers are currently working on various promising concepts for the future, and our acoustics experts are involved in our projects at every stage of product development, from technology management to subsequent engine design and optimization.


New concepts pave the way for zero pollutant emissions

In addition to contributing to climate effects and generating noise, air traffic also has an impact on local air quality at airports and surrounding areas. The combustion process in aircraft engines produces pollutants in the form of nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC) and soot/particulate matter. In terms of the impact these have on health, NOx and particulate matter emissions are the most significant. To obtain type certification, aircraft and engines must meet environmental standards stipulated by the ICAO. ICAO has defined limits for the levels of NOx, CO, UHC and soot emitted by aircraft engines. All of the engines in which MTU holds a workshare meet the ICAO certification standards. Recently, compliance with standards for ultra-fine particulate emissions became a criterion for engine certification. Unlike with noise emissions, we have less scope to influence the health effects caused by NOx and particulate matter because the combustor is not part of our portfolio for commercial engine programs. We can make a difference here only indirectly by improving the efficiency of the engine. For example, with the geared turbofan we have succeeded in significantly reducing NOx emissions, which are 50% lower than those of its predecessor. Sustainable fuels can also make a big difference in this regard. In initial tests, the German Aerospace Center (DLR) has shown that particulate emissions from combustion are significantly lower with sustainable aviation fuels (SAF) than with conventional aviation fuels. Using hydrogen as a fuel eliminates them completely.

80 %
reduction in nitrogen oxides

A pilot concept that we’re backing and for which we’re already making preliminary designs can make aircraft engines remarkably cleaner: The WET engine could reduce NOx emissions by up to 80% in the future. Hydrogen-powered fuel cells would eliminate them completely.

Our development of revolutionary propulsion concepts, which is part of our climate action activities, also holds great potential for reducing pollutant emissions. Our WET engine and fuel cell concepts can minimize pollutant emissions or even avoid them altogether. The WET engine works by injecting water into the combustor, which, based on what we know so far, can cut NOx emissions by up to 80%. Hydrogen-powered fuel cells would emit nothing but water. That’s what we’re aiming for.

Services and tools

Climate impact of aircraft engines
Back to Top
Research and development