TO MEASURE IS TO KNOW: MAPPING NOISE LEVELS

Brussels Airport permanently carries out noise measurements to map the noise pollution caused by the air traffic. The noise contours for the airport are also calculated annually, as described in the Flemish Environmental legislation (VLAREM). These calculations are carried out by an independent body; since 2015, this has been Ghent University.

The airport has been having the noise contours calculated for more than 20 years. In this way we have clearly mapped the long-term evolution of noise impact, the number of movements and the actual runway use. Weather conditions and other events, such as maintenance work, affect the actual use of the runways.


Noise contours as yardstick

How does the airport know how many people living around the airport are ‘potentially highly annoyed’ by noise events from air traffic? By calculating noise contours. The noise contours are lines connecting points with the same average noise levels. Anyone living within the noise contours may experience inconvenience from noise pollution.

According to VLAREM, the international calculation model INM (Integrated Noise Model) of the Federal Aviation Administration (FAA) must be used for the calculation of the noise contours. The noise contours for Brussels Airport are calculated by the team of Dick Botteldooren, Professor of Acoustics at Ghent University.

In the calculations, a distinction is made between day, evening and night contours. These three noise contours are then combined into a single contour (Lden = Level Day-Evening-Night) More weight is given to the evening period (+5 dB) and the night period (+10 dB).

The runway use, the number of (night) movements and the aircraft fleet have the greatest impact on the noise contours. The long narrow contours mark the aircraft landing at Brussels Airport and the wide lines come from the departing aircraft. These make more noise, as the engines are using more power, but the noise disappears more quickly as the aircraft climbs faster.


Example 2018: Lden noise contours

The unit of measurement for ambient noise is therefore Lden, expressed in decibels (dB). In 2018, the area within the Lden noise contour of 55 dB increased by 6% compared to 2017. In comparison with 2000, this is a decrease of more than 45%.

The increase of the Lden noise contour in 2018 had various causes:

• The main reason for this was the relatively frequent occurrence of wind from the east. Approximately 20% of the movements in 2018 had to deviate from the preferential runway use scheme (PRS) stipulated by the Federal Government. Wind limits, expressed as a maximum crosswind and maximum tailwind for each runway, are therefore attached to this runway use. If these limits are exceeded, air traffic control will switch to an alternative configuration in order to ensure safety for passengers and crew. In 2017, this only occurred in 10% of the cases. As a result, other runways were used more than usual, resulting in 'alternative runway use'.

• Another cause is the evolution in the number of movements. Although the total number of movements decreased by around 1% in 2018, there was a slight increase in air traffic during the evening period (7.00 pm to 11.00 pm) and the night period (11.00 pm to 7.00 am). Because of the weighting factor within the Lden parameter (a higher factor), these increases during the evening and night weigh heavier than the decrease during the day.

• In addition to these factors, the population level must also be taken into account. The number of people living around the airport increased by 1.3% in 2018. If the noise contours had been exactly the same as those in 2017, the number of people potentially severely inconvenienced by noise pollution would also have increased, namely with 1.3% due to the population increase within these contours.

Evolution of noise contours

The number of people potentially highly annoyed by noise pollution rose from 13,575 in 2017 to 14,948 in 2018. This number has, however, decreased compared to the situation in 2000, when 33,889 people were potentially highly annoyed. Since 2009, that number has remained relatively constant (around 15,000), certainly in relation to the strong increase in the number of passengers that Brussels Airport has welcomed in recent years, namely 25.7 million passengers in 2018.

Between 2009 and 2018, the number of passengers at the airport increased by more than 50%, an increase of 3.6% compared to 2017. This is because larger aircraft are used for various flights and these aircraft are also better occupied. The modernisation of the aircraft fleet continues year after year, which is positive for the noise pollution around the airport.

New noise monitoring system at Brussels Airport Since 1 October 2018, the airport has been using a completely updated noise monitoring system. 21 measuring stations have been set up along the most frequently used flight paths. Smart software links the measurement data to operational flight data. Thanks to the new noise monitoring system, people living in the vicinity of the airport can consult all possible information on www.batc.be. Furthermore, they can follow the air traffic almost in real time and even see how far a specific aircraft was from their home.

The noise measurements are not used to calculate the noise contours. Ghent University does, however, use these to compare the calculated noise contours to the actual situation.