Reducing engine noise and exhaust gases

Health impact of aircraft engines

As part of our product development, we are working to make aviation considerably quieter and cleaner. Our stated goals therefore include reducing aircraft noise and exhaust emissions to minimize the impact that our products—in the air and on the ground—have on people’s health.


Through our Clean Air Engine agenda, we are pursuing a reduction in aircraft noise emissions in addition to our targets for climate action. At our sites, we carry out noise measurements on our test stands.

Industry, innovation and infrastructure
Responsible consumption and production

We undertake to protect the environment; climate action is one part of this, but our endeavors go further still. With quiet and clean engine concepts, we can improve the situation for residents living near and around airports in terms of noise pollution and local 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 issue of aircraft noise 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 & society.”

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 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 due to the engine’s fan and nozzles; during landing, the aircraft also adds to noise as a result of turbulence around the fuselage, wings and landing gear. 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: We are pushing for Europe’s SRIA noise targets

With our technology agenda Clean Air Engine (Claire), we are pursuing not only climate action targets → Climate impact of aircraft engines, but also targets for reducing aircraft noise emissions. Achieving future noise limits is one of the agenda’s core elements. MTU’s acoustics experts are involved in our projects at every stage of product development, from technology management to subsequent propulsion system design and optimization.

When developing future propulsion systems, we support the goals of the European aviation industry and research sector’s Strategic Research and Innovation Agenda (SRIA), which calls to reduce noise to 65% of its 2005 levels by 2050. With the first-generation geared turbofan, which we developed together with our partner Pratt & Whitney and continue to manufacture, 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% compared to the previous generation.

Less aircraft noise
75 %

smaller noise footprint of our geared turbofan from Claire Stage 1 has significantly reduced the spread of aircraft noise in the sensitive area around airports. The geared turbofan already has over four million quieter flights to its name.

The geared turbofan from Claire Stage 1 has an architecture that harbors vast potential for further reducing noise compared to conventional turbofans. By making improvements to the latest generation, we want to achieve the SRIA goal of a 50% reduction in aircraft and engine noise emissions by 2035 (base year 2000).

According to the SRIA, new engine architectures are even to achieve a 65% drop in noise emissions by 2050 (base year 2000). Our efforts here include our new propulsion concept, the (hydrogen-powered) Flying Fuel CellTM, which can achieve massive reductions in noise because the fan is the powertrain’s sole source of noise. It is set to be ready for short-haul routes by 2050.

New concepts pave the way for zero pollutants

In addition to contributing to climate effects and generating noise, air traffic also has an impact on local air quality at airports and in 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 propulsion systems must meet ICAO environmental standards. 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. In the meantime, compliance with standards for ultra-fine particulate emissions became a criterion for engine certification. Unlike with noise emissions, we have less scope to influence NOx and particulate matter emissions and the health effects 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 (SAFs) than with conventional aviation fuels. Using hydrogen as a fuel reduces them even further.

Reduction in nitrogen oxides
80 %

Our new propulsion concept WET can significantly reduce 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%.

Our development of revolutionary propulsion concepts, which is part of our climate action activities, also holds great potential for reducing pollutant emissions. Our Water-Enhanced Turbofan (WET) and Flying Fuel Cell (FFC) concepts can significantly reduce pollutant emissions or even avoid them altogether. The WET concept works by injecting water into the combustor, which, based on what we know so far, can cut NOx emissions by over 80%. Hydrogen-powered fuel cells would actually emit nothing but water.

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