^{Figure 1. Schiphol airport, surrounding communities and Lden noise contours (source: Actieplan Schiphol 2018-2023)}

Amsterdam Schiphol Airport is the main international airport of the Netherlands, located nine kilometres away from Amsterdam. It is the third busiest airport in Europe in terms of passenger volume and provides 326 direct destinations. The airport has one terminal that includes three large departure halls and six runways (see Figure 2). Schiphol is mainly approached from the North Sea and Flevoland, which is an artificial, low populated island.

^{Figure 2. Runways at Schiphol Airport}

Noise regulations

The applicable noise regulations include limitations for handling, the air traffic, and noise regulations related to the maximum amount of noise. The current noise regulations at Schiphol work on the basis of enforcement points such as the 24-hour period and the night period. A maximum L_den or L_night value applies to each of these points. Noise mitigation strategies and land-use planning have been applied in terms of sound insulation of residential and public buildings or by destructing houses and buildings.

This case study looks at the implementation of a noise abatement operational procedure (NADP2) provide noise relief to communities around Schiphol from departing aircraft. At the same time, it was anticipated that this change would deliver fuel savings for airlines.

Objective

To provide noise relief to communities around airports from departing aircraft.

Approach

Two specific noise abatement departure procedures (NADP’s) were developed to mitigate air traffic noise. The NADP describes the procedure in which the aircraft transits from the high take-off power having extended flaps and slats settings towards a climb phase using climb power and all flaps and slats retracted. The NADP1 departure procedure effectively confines the noise impact within a small area around the airport. NADP2 has a distant cross-over point to become quieter than NADP1 and is most effective to reduce fuel consumption. The main difference is that the altitude at which the aircraft starts accelerating is reduced from 3000 ft (NADP1) to 1500 ft (NADP2).

^{Figure 3. Comparison of the ground speed and the lateral noise exposure between NADP1 and NADP2. The NADP2 departure procedure reduces noise exposure due to a shorter fly over event and a smaller lateral area of exposure than NADP1.}

The noise exposure is shorter due to a higher ground speed when NADP2 is used compared to NADP1. For the NADP2 departure procedure, the flight altitude is lower, which results in a reduction of the lateral noise exposure.

^{Figure 4. Illustration of the climb heights between NADP1 and NADP2. The NADP2 procedure starts with a steeper climb where the acceleration required for flaps and slats retraction starts at 1500 ft.}

1. Identification of the need. Applying the NADP2 departure procedure was expected to save approximately 20-60 kg of fuel per departure, which is beneficial for the airlines as well as the climate. Eventually, there would be less highly annoyed people;
2. Designing the options. There was no knowledge of another approach that would result in comparable benefits;
3. The selection of intervention. Fuel savings and the effect within the noise contours (L_den) were used for decision making. The procedure was recommended to all the airlines. However, in practice, is it difficult to test two departure procedures under the same conditions. An experiment of three control groups was carried out to determine the NADP2 departure procedure's specific effect. Communities were informed ahead of time before the departure procedures were changed, but they were not directly involved in the decision-making process;
4. Implementation. Calculations of fuel savings and noise benefits were carried out. Experiments with actual flight procedures were carried out during a three-month trial using live traffic observations. The usage of the NADP2 departure procedure was expanded and applied to other airlines. Currently, 80% of all departures at Schiphol use the NADP2 procedure.

Changing the departure procedure from NADP1 to NADP2 is beneficial for the climate, for the airlines and the overall noise exposure. However, it comes at the expense of those who live directly underneath the path where the differences are noticeable. Based on the dose-response relationship, the number of highly annoyed people living in the vicinity of Schiphol Airport decreased, however, the benefit for the community depends on the location of the residential area. Overall, the communication with the residents around the airport was effective but needed more involvement of the communities and their participation in the decision-making process.