DALLAS — The noise aircraft make has been reduced by at least 75% in the last 50 years, but there is room for further improvement. Manufacturers try to improve their aircraft every time to make them more efficient, more rentable for customers, and, one of the most important things now, less noisy. For people who like aviation, the noise caused by planes is not a problem, but it is for those who live near airports or do not like aviation. This group is a considerable percentage of the global population and can make significant changes in aviation, like changing planes, changing operation hours, reducing flights, or closing airports. Problems Caused by Noise During February, we talked about Köln-Bonn Airport (CGN) not receiving more regular flights operated by McDonnell Douglas MD-11, and the principal reason was the claims made by the Köln population due to noise pollution. For some years, CGN tried to reduce the MD-11 flights by imposing extra payments to noisy planes, and in two years, they reduced half of MD11 operations from six to three daily. We also know about the expansion plan of the Heathrow Airport (LHR) project being affected due to significant concerns about environmental impact and noise pollution. This expansion plan includes a third runway for the biggest airport in the United Kingdom (UK), indirectly benefiting the country by creating works and increasing airport capacities. Schiphol Airport One of the biggest problems caused by noise pollution can be seen in Amsterdam-Schiphol Airport (AMS), one of Europe’s busiest airports. During the last few years, people who live near the airport and are tired of aircraft noise every minute have tried to convince the Dutch government to reduce slots and change flight hours to ban night flights. In July 2023, the Dutch government approved a reduction of annual flights from 500,000 to 460,000 and eventually to 440,000. This reduction was suspended in November 2023 due to EU and US pressure, but for 2024, AMS will increase landing fees by 14.8%. In recent years, manufacturers have been working on reducing the noise produced by planes. Also, airport administrations have been implementing new laws to reduce the operations of noisy planes and flights during the night hours. But changing engines or flight hours is not the only way to reduce noise pollution; further actions are needed. Modifying Standard Instrument Departures (SID) When the plane takeoff the engines give their maximum power to ascend without problems, but when the engines are making this effort, they make a lot of noise, which means that this phase is critical when we talk about noise. For this, the “Noise Abatement Procedures” were created, which are part of the SIDs of many airports. This procedure does not allow a plane to fly below a certain altitude over specific points, usually neighbors or cities, and avoiding or flying over them at a certain altitude will minimize the noise. Let’s choose Valencia Airport (VLC) as an example: The SID charts said it is impossible to change the original departure route below 6000ft, and only some planes can ask for this, like small planes, helicopters, military aircraft, or governmental flights. This departure route includes banking just after takeoff to follow the Turia River and avoid Valencia city. Engine Noise Suppressors Engine noise is created by the high speed of exhaust gases leaving the engine and mixing with the atmosphere; noise suppression is usually achieved by lowering this velocity; for this, in 1990, NORDAM created a device known as “Hush-kit” that changes the pattern of exhaust gases. The NORDAM kit was designed for the Boeing 737-200 and cost $2.5M per aircraft; the principal customers of this kit were Lufthansa (LH) and Air New Zealand (NZ). Other companies created kits for aircraft with old engines, like Boeing 707 and McDonnell Douglas DC-8. But the old engines are not the only problem, because modern engines also make noise and this needs to be moderated, due to this problem was created the Chevron nozzle , which is used by Boeing in some of their aircraft like the Boeing 747-8, Boeing 787 and Boeing 737 MAX. This nozzle was developed working together with NASA. Also, the Bombardier CRJs use the chevron nozzle on their GE CF34 engines. A320 Family Vortex Generator by Lufthansa In 2013, Lufthansa worked with the German Aerospace Center (DLR) to create a small steel piece that does not allow the air to blow inside a hole in the lower part of the A320 wing. Aircraft equipped with this vortex generator are four decibels quieter on approach. Airport Restrictions on Loud Planes Many airports worldwide have restrictions on loud planes, not allowing them to operate between certain hours (usually at night), imposing some extra fees for these planes, or imposing sanctions if the plane exceeds a specific decibel level. Let’s take AMS The charts also say that aircraft equipped with engines with a bypass ratio smaller or equal to 3 can not take off between 18:00 and 08:00 (local time), for example, MD-80. SImilarly, aircraft equipped with engines with a bypass ratio greater than three can not plan takeoff between 23:00 and 07:00 (local time), for example, Airbus A320. Making a small comparison, in the US, the Federal Aviation Administration (FAA), which is in charge of this subject, is restricting noisy planes, and for this, they are working on operation hours and soundproofing houses located near airports. For example, Boston Logan (BOS) does not allow the operation of stage 2 aircraft between 23:00 and 07:00, and also 11,000 houses and 36 schools located near the airport are soundproofed. The same happens at LHR, where all the houses affected by the airport activity can ask for free soundproofing, and due to the construction of the new runway, £700.000 was approved to cover 160.000 homes. The United States and the European Union are working on regulating and reducing noise pollution to a minimum. Still, they work differently and have different viewpoints on this subject without forgetting their commitment to making aviation less noisy. Featured image: British Airways Airbus A350-1000 landing at London Heathrow (LHR). Photo: Johann Heske/Airways