Aircraft combustion engines generate noise and pollutants. It is possible to reduce both; however, there are trade-offs. Fewer nitrogen oxides mean less fuel efficiency. Also, new propulsion systems take a long time to develop. A long-term framework is therefore required. This includes optimising the control and limitation of climate-impacting nitrogen oxide and black carbon emissions (non-CO2 emissions) in cruise flight. The FOCA is actively engaged in international bodies to this end.
Brief overview
- Optimised aircraft design and engine technology are key to reducing noise, fuel consumption and pollutant emissions in aviation.
- Fuel consumption and CO2 in figures: Since the 1960s, fuel consumption per 100 passenger-kilometres has fallen from 8 litres to less than 3 litres. Fossil CO2 emissions are now well below 100g per passenger-kilometre (compared with over 200g in 1960).
- Pollutants could be reduced further, but this would make aircraft less fuel-efficient.
- The legal framework aims to promote aircraft that offer the best overall compromise between CO2 emissions, non-CO2 emissions and noise.
A closer look
Nitrogen oxides
Ultrafine black carbon
In cruise flight, today’s aircraft engines burn fuel efficiently and with virtually no residue. Modern engines operate at higher pressure and temperature than their predecessors in order to make the best possible use of fuel. However, this generates nitrogen oxides, which are mainly formed from ambient air (nitrogen and oxygen) at high engine temperatures. Higher pressure in the engine allows the use of larger propellers (fans) to increase the efficiency of the propulsion system. While these measures lower CO2 emissions, they result in more nitrogen oxides. It is possible to reduce nitrogen oxides, but only by sacrificing some fuel efficiency. This is because the more complex combustion technology makes the engines somewhat heavier, which increases the weight of the aircraft, and heavier aircraft consume more fuel.
Today’s aircraft engines emit very little black carbon (commonly known as soot) in relation to their weight. However, the particles are extremely small and very numerous. Black carbon particles influence air quality at airports and the formation of contrails, and so they need to be reduced. Unlike with nitrogen oxides, with black carbon there is no trade-off with CO2 reduction in the development of new engines. Black carbon emissions depend on the engine technology and the fuel used. Engines already exist that emit around 50 times fewer black carbon particles during cruising than other engines with a similar fuel consumption. The FOCA is working to create a framework in which the engines of the future produce fewer black carbon emissions.
Noise
In the past, less noise also meant less fuel consumption. This was true as long as it was possible to make the propellers (fan engines) bigger, and as long as the fan shroud and the large volume of fan air were able to shield the engine’s loud, hot exhaust jet ever more effectively. While large propellers provide the most economical propulsion, it is no longer possible to shroud the propellers once they reach a certain size. Large propellers therefore produce a low hum. In other words, measures to reduce fuel consumption can lead to noise issues. Future propulsion systems will therefore need to strike a balance between noise emission and fuel consumption.
A sound framework
Environmental standards and other framework conditions are intended to incentivise airlines to select products that offer the best overall compromise (CO2, non-CO2 and noise) when renewing their fleets. In addition to CO2 and noise reduction, the regulatory framework must also include non-CO2 emissions.
The aviation industry works with global standards established by the International Civil Aviation Organization (ICAO). The FOCA is involved in the ICAO Committee on Aviation Environmental Protection (CAEP) and the associated working groups. The existing standards relate to the reduction of pollutants at airports and not directly to emissions during cruising. There therefore needs to be an additional focus on climate-impacting non-CO2 emissions in cruise flight. The FOCA is driving forward work to reduce such emissions. For example, it was heavily involved in the development of a system for measuring and limiting black carbon particle emissions (PDF, 888 kB, 17.02.2025). The method and limit values are today implemented globally as ICAO Standards. The FOCA is proposing that the standards be extended in order to better control black carbon particles during cruising.
Similarly, the FOCA is working within the ICAO on the development of an extension to the nitrogen oxide emissions standard. The goal is to regulate nitrogen oxides during cruise flight and to introduce internationally applicable limit values. Since most nitrogen oxides are produced when aircraft are cruising, the greatest scope for reducing them is during cruise flight.
Further Information
Last modification 19.06.2024
