An airway (‘bandwidth’) is necessary due to changing weather conditions (wind direction, wind speed, temperature, humidity), different types of aircraft and differences in navigation equipment in the aircraft and on the ground. All these factors can influence accurate following of the prescribed route. Deviations from this route are tolerated, as long as the aircraft remains within an airway.
Schiphol lies in the middle of towns and villages. It is not possible to draw a straight line from Schiphol to the national borders without the flight crossing built-up areas.
An aircraft cannot fly a ‘zig-zag’ route that avoids built-up areas. This is partly to do with limitations in the navigation systems and with safety and efficiency requirements. In practice, therefore, the flight routes consist of straight paths, connected by more or less circular bends. The number of bends is limited here. Efforts are made to fly across thinly-populated areas as far as possible. The routes from the Polder runway are an example of this.
Yes. Only the aircraft that take off from the Polder runway follow a special night-time departure route at night, heading North after the take-off before turning South or South-East. These routes were designed to avoid the high population concentrations around Amsterdam or to fly across them at the highest altitudes possible. This leads to less noise pollution at night. A number of special departure procedures also apply for the Kaag runway at night, in a north-easterly direction. The use of these night-time departure routes is only possible when air traffic levels are low. As a result, these night-time routes cannot be used during the day.
In principle, the captain must follow the prescribed outbound route and must remain within the tolerance area. However, the captain must deviate from the route if he receives instructions to do so from LVNL. He may also request the permission of LVNL for a deviation himself, for example in order to avoid severe thunder storms.
Safety takes priority in aviation. In order to avoid a dangerous situation, LVNL may instruct captains to deviate from their route. Sudden changes in weather conditions may also be a reason for deviations. Another reason why LVNL may issue additional instructions is to avoid take-off delays during peak periods. LVNL aims to limit the number of outbound flights by jet aircraft above connected built-up areas at an altitude of less than 3,000 feet (about 900 metres) as a result of such instructions to no more than 3% of the total number of take-offs by jet aircraft.
If a captain flies outside this area without an explicit instruction from LVNL to do so, the Transport and Public Works Inspectorate will open an investigation. This could lead to criminal prosecution, with the court possibly imposing a fine on the captain.
Propeller-driven aircraft are often instructed by air traffic control to deviate from the standard route (Standard Instrument Departure, SID). This is done in order to keep the SIDs free for faster jet aircraft traffic. This traffic would face delays if it had to follow the slower propeller-driven aircraft. As this is contrary to the mainport development of Schiphol, it was decided in the past that propeller-driven aircraft can be exempted from following the SID routes.
A number of ‘holdings’ or ‘stacks’ have been designated at some distance from Schiphol. These are intended to keep incoming aircraft in a holding pattern at very busy times and during unforeseen weather changes. These aircraft circle in a holding pattern until they receive clearance from air traffic control to land.
In the holding, the aircraft are ‘stacked’, as it were. They fly in a fixed patter there, on 'race tracks', maintaining a minimum vertical distance from each other of 1,000 feet (more than 300 metres).
Depending on the volume of traffic, aircraft in a holding pattern can usually be found at an altitude of between 7,000 feet (about 2,100 metres) and 24,000 feet (about 7,500 metres). Aircraft enter the holding ‘from above’. The main holdings are situated above the IJsselmeer, near Lelystad, above the Zeeland islands and above the sea to the west of North Holland province.
The use of holding patterns does not entail any extra risks. Strict safety standards apply for the distance that aircraft must maintain from each other in both a horizontal and vertical direction.