In the aviation sector, reference is made to ‘dependent runway use’ if flight operations on one runway (can) affect flight operations on another.
The use of take-off and landing runways is determined on the basis of various factors, such as weather conditions, runway availability, environmental rules and traffic volumes. These factors and the lay-out of the runway system mean, for example, that combinations of dependent runways often have to be used at Schiphol.
When are runways dependent
Take-off and landing runways can be dependent on each other in different ways. Runways may literally intersect, as the Aalsmeer and Buitenveldert runways do at Schiphol. If the runway lengths cross, we refer to ‘converging runways’. Dependent runway use also occurs with the use of parallel runways and the use of a runway for both take-offs and landings - known as the ‘mixed mode’. Runway combinations are also possible in which departing aircraft can cause jet blast hazards for other air traffic, such as with simultaneous use of the Kaag and Aalsmeer runways. Jet blast is rapid air movement produced by the jet engines of aircraft, particularly on take-off.
Safety procedures
Despite the dependence of runways, it is possible to create conditions in which runways can safely be deployed simultaneously. Air traffic control therefore has different procedures for dependent runway use than for independent runway use.
Some examples of the additional conditions for dependent runway use are:
With dependent runway use, strict conditions are imposed for the visibility conditions. There are minimum values for visibility and/or the cloud base, for example, and in daylight different procedures apply from those for when it is dark.
With reduced visibility conditions, the distance between aircraft during landing and/or take-off is increased, by increasing the time intervals in this traffic flow, for example, or by timing take-offs and/or landings in relation to each other. Both affect the volume of traffic that can be handled. More information on separation of aircraft can be found here.
Depending on the circumstances, additional conditions are imposed, for example for the available system support, the availability of runway lighting and the number of active air traffic controllers.
