Weather Dependent Separations

Developed in the SESAR context, the Weather Dependent Separations (WDS) project for both arrivals and departures is aimed at optimising aircraft spacing – it reduces or suspends wake separations – by taking into account all meteorological conditions (crosswinds, headwinds, turbulence and temperature) and wake vortex behaviour.


Current aircraft separations are designed for all weather situations; they use conservative spacing in wind conditions that help to dissipate wake turbulence. How can WDS take advantage of wake behaviour to increase throughput?


The current Time-Based Spacing concept only takes headwinds affecting aircraft performance into consideration when reducing the distance between a pair of aircraft. WDS extends this to crosswinds or total winds (headwind and crosswind) conditions, which can increase capacity and throughput proportionally to the number of wake-constrained pairs.

The concept is based on wake turbulence behaviour under different wind situations. In strong crosswind conditions, wake turbulence is blown out of the path of following aircraft, thus reducing or even removing the need for wake vortex separations. The overall wind situation is assessed based on how quickly wakes dissipate in the strength of wind.

Weather Dependent Separation has several modes of operation, since it can be activated with DBS or TBS, and under crosswind or total wind conditions. Its application also requires the Optimised Separation Delivery tool, as developed for TBS, RECAT-2 or RECAT-3.

Activation of WDS will increase runway throughput while TBS is intended to maintain it in all conditions. This additional throughput can be used tactically either for delay reduction or for capacity benefits, if enhanced throughput is coordinated with the flow management and MET offices.


  • Weather Dependent Separations increase arrival and departure capacity, due to reduced spacing between aircraft under different weather conditions (headwind, crosswind, total wind) and wake behaviour.
  • Enhanced throughput and better management of fluctuations help reduce runway queuing delays.
  • Safety levels are maintained, as wake dissipation makes reduced distances between aircraft possible.
  • WDS gives ATCOs greater flexibility in managing the traffic mix, due to the separation minima reduction.
  • Since WDS requires weather forecasts and wake turbulence data, this information will be made available.


WDS will be of particular help to capacity and wake-constrained airports, as it enhances throughput and allows the airport to operate at a high level of efficiency in all meteorological conditions.

For airports where Time-Based Separation or the Optimised Delivery tool have already been deployed, WDS can easily be implemented as it will only need a minor system update.

Vincent Treve

Runway Throughput & Wake Project Manager
+32 (0)2 729 5197