Why do Schiphol and municipalities each say something different about noise nuisance?

A plane taking off at Schiphol. (Photo: ANP).

The Leiden region complains a lot about noise nuisance from Schiphol. Data from the BAS reporting center and the Danish Environmental Protection Agency show that the number of complaints and night flights increased explosively last year. This is mainly due to the use of the Kaagbaan at Schiphol as a runway for a large part of the landing and take-off air traffic in the Netherlands. Also in the evening and night hours. Nevertheless, air traffic control at Schiphol (literally) has a completely different view of this file.

It is not yet officially known how many planes have flown over the heads of residents in the Leiden region this year. The Environmental Protection Agency in West Holland only reports once a year on the measuring points present in the region. The report for 2022 is expected early next year. The municipalities use these reports in discussions with Schiphol, and they are therefore important in relation to deciding on aircraft noise nuisance.

Then we come into contact with Schiphol’s air traffic control (LVNL), and we receive a data set of the flight movements over the various municipalities in the region quite exceptionally. The dataset contains the number of flight movements from 2018 to the beginning of November 2022. We compare the air traffic control dataset with data from the Danish Environmental Protection Agency, and something strange stands out. The air traffic control data does not correspond to that of the Danish Environmental Protection Agency, in fact they differ enormously from each other.

Deviate
If the measurement points in Sassenheim (part of Kaag en Braassem) registered between 55,000 and 65,000 aircraft over the municipality in 2021, according to air traffic control, just under 11,000 aircraft flew over Sassenheim in the whole of 2021. Approximately 40,000 fewer aircraft than the registered measurement points.

The same picture can also be seen in Leiden. According to air traffic control data, almost 21,000 aircraft flew over Leiden in 2021. In Leiden Merenwijk, however, the measuring point recorded more than 35,000 aircraft. More than a third more. In Nieuwkoop, the difference is even greater, the Danish Environmental Protection Agency reports more than 60,000 aircraft in 2021, air traffic control only 15,000. A difference of no less than 45,000 flights.

Shocking
Regarding night flights, the difference between the two authorities’ figures can be called shocking. According to the Danish Environmental Protection Agency, almost 4,500 night flights took place in Leiden between 23.00 and 07.00 in 2021. Air traffic control registers a fraction of this: 531 night flights in the whole of 2021.

The Environmental Protection Agency’s measuring stations have measured flights that, according to air traffic control, have not taken place at all. This is remarkable because the measurement points consist of a microphone and computer. This computer checks whether the measured sound corresponds to the transmitter on board a victorious aircraft. This transmitter transmits data about the position of the aircraft in question. If this corresponds to the perceived sound, the aircraft is only registered at the measurement point.

To deviate
Not only do we find notable large differences between the two data sets for 2021. Regardless of which municipality we look at, the figures from 2018 to 2022 are still markedly different.

We are contacting both the Danish Environmental Protection Agency and air traffic control to find out the reason for such deviating data. The air traffic control spokesman said in a response: “When we provided our data, we specified exactly which geographical area and on the basis of which altitude an aircraft movement of Schiphol traffic must have taken place in order to be counted. The definition of the environmental service may differ from the definition used by LNVL, which can lead to mutual differences”, reads the reply.

Measuring systems
We will not get much further in the Environmental Service. The service has kept its doors closed for the past few months and is not responding to repeated requests for information. Just before the publication of this article, the Environmental Protection Agency West Holland issued a response: “We are aware that there are differences in the figures reported by air traffic control and the municipalities. A likely reason for the difference in numbers is the difference in the measurement systems used.”

“The Schiphol system (NOMOS) has a higher lower limit (60-65 dB) than the measurement points that the Danish Environmental Protection Agency works with. This can lead to more observations at measurement points. Another possible explanation is that new links have been made on the Sensornet, which can be used to determine when aircraft noise is involved, rather than other ambient noise (such as a passing car). The latter has in recent years led to a significant increase in the number of registered aircraft movements within the Sensornet measurement network.”

Structural
We also knocked on the door of the Ministry of Infrastructure and Water Management (I&W), which is responsible for air traffic in the Netherlands, but we also received no response. At the I&W Ministry, which is responsible for aviation, there is therefore a completely different picture of aircraft nuisance than the one measured on the ground by the Environment Agency and experienced by the residents.

The question is why these deviations in numbers have not been noticed before. Various municipalities in the Leiden region, which consult with Schiphol, use data from the Danish Environmental Protection Agency. At the air traffic control desk, you must have noticed that these numbers are structurally different. And what figures lead in discussions about flight problems? Due to the environmental service reports, the municipalities have the impression that air traffic has increased explosively, while air traffic control is particularly quiet over the Leiden region. The air traffic control figures are leading and are reported to the Ministry of I&W.

Member of Parliament
We present the differences to MP Mahir Alkaya (SP): “As SP, we also note that there are more complaints about flight nuisance from the Leiden region. The differences between the results of the BAS reporting center and the Danish Environmental Protection Agency on the one hand and LVNL on the other are remarkably large and we (and experts and experienced experts in our network) cannot yet explain them at the moment. This may be due to differences in measurement methods, or there may actually be a difference in definition. In any case, the deviations in the number are so great that it must be clarified.”

Consultation platform
Since October this year, the consultation structure with Schiphol has changed. A new platform, where a total of 56 municipalities and 4 provinces are represented, has served as the official discussion partner since the end of last year. A large part of the Leiden region is now also part of Schiphol’s ‘noise contour area’, or the area that can be affected by aircraft. According to the new agreements, the government, provinces and municipalities in the vicinity of Schiphol will jointly implement measures. In response to this article, several municipalities in the Leiden region expressed their hope that this new consultation platform would enable them to exert more influence to reduce air nuisance.

The new noise-generating contours of Schiphol. (Image: Omroep West).

The municipalities in the Leiden region are facing important months. Not only will air traffic continue to increase, noise nuisance for residents will also increase. And then there is also the discussion surrounding the construction of the second Kaagbaan at Schiphol.

The outlook for residents who experience nuisance from planes is not exactly positive. Many municipalities have no insight into aircraft nuisance or read this back a year later in the Environmental Service reports. In addition, different figures are available on the number of flight movements over the Leiden region, where the ministry works with air traffic control figures that are a fraction of the measured flight movements in the region. As a result, the ministry will lack the need to enforce flight nuisance in the Leiden region. Reporting nuisances to hotlines also does not seem to have initiated any change.

Protection
The question is, who will protect the residents of the Leiden region from the potentially harmful consequences of aircraft noise pollution? The answer to this has not yet been guessed.

This week, media partner Omroep West publishes a series of stories about noise pollution from Schiphol to the Leiden region. This series is made possible in part by Leids Mediafonds.

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