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Focus: infringements by air traffic due to noise nuisance

After an increase between 2005 and 2007 the number of infringements related to noise caused by air traffic decreased again between 2007 and 2012. The number of official reports of the offences in particular dropped significantly. A possible explanation for this could be found in various factors, the most important being the evolution of air traffic.

Flights over the Brussels territory are subject to rules

Certain limit values apply to flights above the territory of the Region. These have been laid down in the ruling (Ordonnantie) of 27 May 1999 of the Government of the Brussels Capital Region on measures against noise nuisance caused by aircraft. These limit values have been established according to two periods of observation (day and night) and according to three geographical zones (0, 1 and 2), which have been defined based on the distance to Brussels Airport, zone 2 being the one located closest to the airport. The limit values are stricter for the night-time period than for the day-time period, and stricter as the distance to the airport increases.
Bruxelles Environnement-Leefmilieu Brussel monitors compliance with this ruling. The noise generated by air traffic is measured continuously in the 9 noise monitoring stations located under the main air corridors. Eight of these are actually used to detect infringements. This monitoring network covers all flight routes above the Brussels territory. The environmental police then determine which of the noise events related to passing planes exceed the applicable limits.
In case of exceedance of the limit values a warning is given. An official report is drawn up if the measured value exceeds the limit value by more than 6 dB(A) at night and 9 dB(A) during the day. The warnings are intended to encourage airlines to remedy the excessive noise levels. The official reports are also submitted to the Public Prosecutor, who may initiate legal proceedings against the airline or return the case to Bruxelles Environnement-Leefmilieu Brussel in order for the procedure of the administrative fine to be applied. Until today, the Public Prosecutor has always opted for the latter procedure.

Number of infringements related to noise nuisance by air traffic dropped in 2012 compared to 2007

Based on the noise levels measured by the monitoring network, for each year between 2005 and 2012 an analysis was made of the number of flights that exceeded the limit values (i.e. which committed an infringement): this analysis provides an overview of infringements according to the time of day and according to the type of sanction. In case several infringements are detected for a single flight (e.g. at various monitoring stations or in different zones) or various sanctions are imposed, only one infringement will be counted, that is the one that corresponds to the most severe sanction.

Figure: Number of flights (2005-2012) in Brussels Airport that exceed the limit values of the ruling of 27 May 1999, according to observation period (day/night) and type of sanction
Source: Bruxelles Environnement-Leefmilieu Brussel, noise and monitoring database, 2013
Observation periods according to the ruling: day (7 a.m. - 11 p.m.) / night (11 p.m. – 7 a.m.)
Type of sanction: W = warning / OR = official report


Figure: Number of flights (2005-2012) in Brussels Airport that exceed the limit values

The large majority of exceedances (over 99% of all flights committing infringements) can be ascribed to planes that are taking off. This can be explained to a large extent by the configuration of the airport: landing and taking off preferably take place against the wind, which normally blows from the southwest. Therefore, planes usually take off in a west direction and come from the east when landing. Hence, the aircraft flying over the Brussels territory are mainly planes that have just taken off from the airport.
In the period 2005 to 2012 most (56%) flights that exceeded the noise limits took place during the day, between 7 a.m. and 11 p.m.. These exceedances mostly resulted in warnings (97%) because the limit values were exceeded by less than 9 dB(A).
Of all night-time flights that exceeded the noise limits (44% of all flights committing infringements), a larger number were sanctioned with an official report (17% compared to 3% of flights during the day). We would like to point out once more that in the case of night-time flights an official report is drawn up for smaller exceedances of the limit value than in the case of day-time flights (6 dB(A) compared to 9 dB(A)) and that at night a lower limit value applies than during the day.
Over the past 5 years significantly less official reports were drawn up (this is true for both the number of flights committing an infringement and the share of official reports), regardless of the period of observation. The number of flights for which a warning was issued also decreased, but the share of these flights in the total number of infringements observed has risen for the period between 7 a.m. to 7 p.m. and at the end of the night (6 a.m.–7 a.m.).

Factors that influence noise emissions and nuisance caused by air traffic

Various factors affect noise emissions and noise nuisance caused by air traffic, and hence also the exceedances of the limit values:

  • Air traffic: the more aircraft fly over the territory of the Region, the higher the number of potential infringements. Around half of all flights that depart from or land at Brussels National Airport actually fly over the Brussels Region. Due to the configuration of the airport (see above) these are mainly planes that are taking off.
  • Strips and flight routes used: a specific system of preferences applies to the strips to be used in Brussels Airport. Around the airport planes fly according to predetermined flight procedures or routes: it appears form the acoustic site description of the regional territory, which is based on modelled noise levels for air traffic, that certain flight routes are predominant (cf. the indicator “noise register for air traffic”): nearly three quarters of all flights that exceed the limit values are concentrated on 4 flight routes.
  • Atmospheric conditions: the weather conditions in winter, especially the low temperatures, are more favourable to gain height fast. The monthly partition of the total number of flights and the total number of flights exceeding the limit values shows that the seasons have a clear influence: in winter there are less exceedances than in summer. Temperature undoubtedly plays an important role.
  • The characteristics of the fleet used (i.e. the aircraft): the noise produced by an aircraft depends on its size and engine type. As a general rule, we can say that the larger and heavier a plane, the more noise it will produce. In addition, technological developments result in less noisy planes. Hence, airlines can reduce the noise nuisance produced by their aircraft fleets when they replace their aircraft.
  • Regional, national and/or international regulations: this factor must not be underestimated. In this respect, we can mention, for instance, the ban on obsolete and very noisy aircraft (such as the Boeing 727, which used to represent a large section of the fleet of certain airlines). Furthermore, various measures are in place to limit movements during the night. There are also differences between the regulatory period and the period of the airport activities: when we calculate the average number of flights per hour that commit infringements we see a peak of infringements between 6 a.m. and 7 a.m., which cannot only be explained by the average traffic per hour. According to the Brussels’ ruling this time block falls within the night-time period, but operationally speaking it is considered to be part of the day-time activities of the airport; this plays a very important role here.

Key position of air traffic in explaining the downward trend of the number of infringements

A number of the factors mentioned above can explain certain fluctuations between the years (strips and flight routes used, weather conditions), this is not the case though for the downward trend in the number of flights committing an infringement as recorded over the past 5 years.
To explain this trend, the analysis of the number of flights committing infringements between 2005 and 2012 has exposed the importance of the role of air traffic. The change of the number of flights committing infringements is closely related to air traffic. For instance, air traffic increased slightly between 2005 and 2007 as a result of the arrival of new airlines and the opening up of air routes. After that, there was a significant drop (-14% between 2008 and 2012) after the economic and financial crisis broke out in October 2008. This drop was even more pronounced due to the negative impact of the eruption of the Icelandic volcano in April 2010 and the large-scale social movements in 2012. In particular, air traffic during the night dropped from nearly 25,000 movements between 2005 and 2007 to 14,000 movements between 2009 and 2012, as a result of the disappearance of an airline that represented a large volume of traffic and due to numerous regulatory measures.

Figure: Air traffic in Brussels Airport and percentage of flights committing infringements (2005-2012)
Source: Brussels Airport Company for the number of flights at Brussels National Airport; Bruxelles Environnement-Leefmilieu Brussel for the number of flights exceeding the limits of the ruling of 27 May 1999


Figure: Air traffic in Brussels Airport and percentage of flights committing infringements (2005-2012)

However, air traffic is not the only cause that can explain the change of the number of infringements.
The study of the fleet used has also exposed a few interesting trends. Around 90% of all traffic consists of aircraft with an average body width and 10% of aircraft with a wide body; the share of light aircraft is very small. In the period 2005 to 2012 average-sized aircraft traffic dropped by 13%, while jumbo jet traffic rose by 6%. The increase in the latter type can be ascribed to an increase during the day-time period, which compensates a 50% drop during the night-time period (effective drop since 2007). This decrease in night-time movements of jumbo jets – to which stricter limit values apply – may also play a role in the drop recorded since 2007 in the number of official reports issued during the night-time.
Finally, changes in the regulations – at the regional (mainly Flemish), national and/or international level – also affect the number of flights that exceed the limit values.
We can conclude that the downward trend in the number of exceedances recorded over the past 5 years and, in particular, in the number of official reports, is not only related to the decrease in air traffic. The changes in jumbo jet traffic and in the regulations may also have contributed to this trend.

Sources

  • BRUXELLES ENVIRONNEMENT-LEEFMILIEU BRUSSEL, 2013. Fact sheet no. 39 on the topic of Noise in Brussels, 'Analyse van de inbreuken die verband houden met de geluidshinder van het luchtverkeer in het Brussels Hoofdstedelijk Gewest'; an update of the fact sheet of May 2005 is under preparation.
  • BRUXELLES ENVIRONNEMENT-LEEFMILIEU BRUSSEL, 2013. Database of noise events of air traffic that exceed the regulations. Subdivision Curative Police.
     
Date de mise à jour: 13/12/2017