Residents’ organization PUSH has discovered errors in calculations of noise levels around Schiphol. After repeated insistence, the Minister of Infrastructure and Water Management acknowledged the mistake and apologized. According to residents, – in theory – an additional 50,000 flights would have been possible above their homes if the error had not been discovered.
According to PUSH, the club that represents residents of Schiphol in Uithoorn, the calculated noise values for 2026 were much too high at enforcement point 25 in Uithoorn.
The error was in figures that Schiphol had provided for the runway maintenance scheme and that were later also used by the ministry. This is a temporary set of agreements that applies when Schiphol’s runways are maintained.
Although the arrangement was not yet final at the time, the ministry and the Netherlands Aerospace Center (NLR) did not notice the errors. NLR should have noted during the so-called counter-expertise that the data and calculations used were incorrect, but overlooked this.
Big difference in sound values
The error came to light after PUSH and the Schiphol Social Council discovered that the calculated noise value on paper was remarkably high compared to previous years.
“I had the feeling that something was wrong. I saw that the figures were much too high, but every time my questions were waved away by both the ministry and Schiphol,” says PUSH chairman Mirella Visser. After insisting, she finally received an affirmative response from Schiphol after almost two weeks that a mistake had indeed been made.
“It was such a big difference that I find it incomprehensible that no one at Schiphol and the ministry saw it. It was not about tenths, but about 1.7 to 3 decibels.”
Software error
According to Schiphol, there was a ‘minor software error’ in an older calculation model that is temporarily still required to be used. The error is said to be deep in the system and should have been repaired immediately with the software manufacturer. All calculations were then checked and the process surrounding the exemption application was continued with new (lower) values.
It remains unclear why these errors were not discovered earlier. “We carry out several internal checks on this ourselves and the ministry has an independent counter-expertise carried out. However, these checks look at a different level of detail, so this specific error was not immediately visible,” said a spokesperson.
According to Schiphol, the incorrect calculations were actually to the detriment of the airport. The software error caused the expected noise level to be calculated too high. On paper, it seemed as if Schiphol would cause more noise pollution than was actually the case. When applying for an exemption (such as for maintenance of runways), an excessively high noise estimate can mean that permission becomes more difficult.
Sorry
In a letter to PUSH chairman Mirella Visser, the minister acknowledges that incorrect data has been used. In the letter, the minister leaves little room for doubt about the error and calls it ‘regrettable’. He also expresses his gratitude for PUSH’s ‘attention’.
PUSH calls the issue serious. “It really is a serious mistake. We calculated with local residents that with those three decibels extra, they could have carried out around 50,000 extra flights via the Aalsmeer runway if we had not discovered this. In theory, because other rules would not have allowed this,” she explains.
Schiphol has announced that such a number of additional flights on the Aalsmeer runway would never have been possible, because Schiphol indeed flies according to the so-called preferential runway use. This means that the airport consciously chooses certain runways earlier when taking off and landing, in order to limit noise pollution as much as possible.
PUSH chairman Mirella Visser mainly wonders how local residents can trust the calculations made by Schiphol. “It also shows that everyone accepts what Schiphol says and publishes is correct.”
“This shouldn’t have happened”
Schiphol has now rechecked calculations from the period 2019 to 2025. According to Schiphol, the same error was not found. The ministry has announced that it will evaluate the control system with Schiphol and the NLR.
“We understand, of course, that the incorrect calculation does not contribute to the confidence of local residents,” the ministry said in a response to NH. “This shouldn’t have happened.”
