• AIRCRAFT NOISE:

    How can it be minimised?

For aviation enthusiasts, the sound of aeroplane engines is music to their ears, but for people who live near airports or airfields, it can be quite annoying. That’s why there are procedures to minimise aircraft noise, and today we’ll explain what they are.

But let’s think back: when did aircraft engine noise begin to be muffled?

In the early years of aviation, when the number of aircraft was very limited, they used piston engines, so the noise stopped once you moved a few metres away from the aircraft.

It was not until 1920, when aviation began its golden age, that the problem of increasing noise pollution was identified. The aviation business grew exponentially with the rise of commercial flights.

Finally, in 1949, with the first commercial jet flight of the De Havilland DH106 Comet, the jet era began; and in 1970, the FAA, the US aviation authority, began regulating aircraft noise emissions.

How is aircraft noise measured?

The unit of measurement for sound is the decibel, dB, and the devices used to measure it are sound level meters.

To give you an idea, a normal conversation is about 50 dB; a hoover running can reach 90 dB; and a plane taking off would reach 120 dB. And you might think that, on the face of it, it doesn’t make much difference, right?

But you have to bear in mind that sound does not increase linearly but exponentially: a difference of 3 dB more means that the sound has doubled, while 3 dB less means that it has halved.

In other words, if we go back to the examples at the beginning, the take-off of an aeroplane can make the same noise as more than 1000 hoovers turned on at the same time. Mind-blowing, isn’s it?

What are Noise Abatement Procedures NAP?

To minimise aircraft noise, Noise Abatement Procedures, or NAPs, have been developed, which are based on modifying certain phases of flight.

For example, if during an instrument departure the minimum altitude is 1000 feet, when NAPs are active it becomes 3000 feet. In this way, the noise perceived on the ground is much lower.

Another option to dampen aircraft noise on the ground is through flight path planning in order to avoid the most populated areas at night and in the early morning hours.

These procedures do allow the use of engine reversals for landings and, in an emergency, the pilot in command can abandon them and continue with standard operations.

When does an aircraft make the most noise?

The initial climb is the noisiest phase of a flight because, during take-off, the aircraft has to gain speed while rapidly increasing its altitude.

In contrast, the approach or landing is a much quieter phase. Nowadays, what are known as ‘green approaches’ are carried out: much more direct arrivals that allow approaching airports with lower power settings.

Interestingly, before each flight, pilots must check the aircraft’s noise certificate. The noise certificate is a booklet that specifies the aircraft’s registration number and the decibels it emits during each phase of flight.

Did you know that…?

Concorde is the fastest — and noisiest — airliner ever to have existed. With a cruising speed of up to Mach 2, i.e., twice the speed of sound, Concorde was severely limited by noise.

It could only reach its top speed over water, so that the explosion caused by breaking the sound barrier would not disturb the lives of people on the ground.

For example, on a flight between Berlin and New York, it could only break the sound barrier over the Atlantic Ocean; while flying over the continent, it had to remain at lower speeds.

New and quieter aircraft

Today, manufacturers are increasingly aware of the noise their aircraft produce. For this reason, they are investing heavily in designing engines that are not only more efficient, but also quieter.

One example is the Silent Aircraft project, launched a few years ago by Embraer, the world’s third largest aircraft manufacturer.

After detecting and evaluating the noise generation of its aircraft, Embraer created the E195-E2, an aircraft 75% quieter than its predecessor, which already operates in Spain with airlines such as Binter.