How can aircraft noise be reduced?

06 February 2025

Aeroplanes are amazing machines – but they are amazingly loud. The noise they make can be a nuisance, so how can aircraft be made quieter?

Noise starts by getting on your nerves – and in the long term it can make you sick. People who live on busy roads or in the flight path of an airport are more likely to struggle with sleep and concentration disorders and a significantly increased risk of tinnitus, high blood pressure and cardiovascular diseases.

Although aircraft have become around 75 percent quieter in recent years, air traffic has increased significantly over the same period. Chronic noise pollution causes 12,000 premature deaths every year. According to the EU, the same number of schoolchildren are suffering from learning deficits simply due to aircraft noise. The aim, therefore, is for aircraft noise in Europe to be reduced by 65 percent by 2050.

The two biggest noise factors in aircraft are engines and aerodynamics – and they interact with one another. With suboptimal aerodynamics, the air resistance increases, and increased thrust is needed from the engines to overcome it.

That the engines make so much noise in the first place is due to the combustion of the fuel and the enormously accelerated air, which is pushed out of the back of the engines as if by an enormous hairdryer, propelling the aircraft forward.

From an acoustic point of view, aircraft builders have already made progress here, for example through the development of the turbofan engine. In this type of engine, some of the air bypasses the compression core, providing a kind of sheath for the inner air flow. The outer air mass acts like a silencer. Because these engines also consume less kerosene, they are now standard on virtually all civil aircraft with engines.

A special feature, however, is the sawtooth-shaped trailing edge on the engines of the Boeing 787. The “chevron nozzles” ensure that air currents of different speeds mix better and thus produce less noise.

At take-off, it is the turbines which make by far the most noise. During landing, on the other hand, 30 to 50 percent of aircraft noise is caused by the landing gear, flaps and other factors that exacerbate air turbulence. This is why researchers in the EU-funded “Inventor“ project are experimenting with porous materials on flaps and landing gear to change the airflow and quieten everything down.

What makes which noise on an aircraft body can sometimes only be determined in the course of elaborate investigations. The German Aerospace Centre (DLR) subjected the acoustic properties of the Airbus 320, which was attracting negative attention due to its high-pitched whistling sounds, to close scrutiny. The experts found out that the sounds were being produced by air flowing over the tank pressure compensation aperture under the wing – rather like the mechanics of blowing into a flute. DLR therefore developed a device to redirect the air flow and prevent these unwanted whistling noises.

Completely new aircraft designs should also make it possible to turn down the noise. Today’s aeroplane is basically a tube with wings. In the blended wing-body concept, on the other hand, the fuselage merges smoothly into the wings. This reduces air resistance, fuel consumption and noise.

The Bauhaus Luftfahrt think tank has presented the concept of an aircraft with a closed wing that surrounds the aircraft body like a frame. With this design principle, taken from the box kite, there is no turbulence on the wings, which also reduces air resistance, fuel consumption and noise.

In order to protect residents from excessive noise, aircraft are now also allowed to take off at a steeper angle. In this way, they spend less time flying over residential areas at an audible altitude. When they are coming into land, planes can wait as for as long as possible at high altitude whenever there is a queue for the runways. And because the air vortices around the flaps and landing gear make so much noise, the latter can be extended at the last minute, allowing the plane to glide towards the runway with as little engine use as possible – this is the principle of the “Frankfurt Process” developed at Frankfurt Airport, which has now spread worldwide. Some airports also change arrival and departure routes during the day to distribute the noise more evenly among the surrounding residential districts.

In point of fact, loud aircraft are becoming more and more expensive for the airlines. This is because airports in Germany are legally obliged to include noise in the calculation of their airport fees. Quieter aircraft take off and land more cheaply than loud ones – and the airlines are clearly feeling the effects of this in their bank balances. At Cologne/Bonn Airport, for example, the “noise surcharge” now accounts for up to a third of the total airport charges.

How noise surcharges are set varies from airport to airport. Some, such as Nuremberg Airport, base their charges on the noise category determined during aircraft registration. Others, like Frankfurt, Hanover, Hamburg and Munich, classify the aircraft into categories based on the noise measured on site.

Berlin’s BER is the first airport in the world to go one step further. Since September 2022, the airport has been measuring the noise made by each individual aircraft and charging the airlines accordingly: Aircraft in the quietest noise category are already costing the airlines 40 euros, jumping up to a whopping 7,500 euros for the noisiest planes.

According to BER, the measures have already made a palpable difference: Several airlines have already switched to the quieter steep take-off procedure. And more and more are flying aircraft of the latest – quieter – generation to BER. Since the beginning of individual measurements, their share has almost doubled to its current level of 25 percent.