Departure Sequencing and Separation

The spacing required between departures should depend on aircraft wake turbulence category and the assigned SID. For example RECAT EU (used at many major EU airports) requires 120 seconds between the departure of an A380 and a following B737. Separation may also be required between aircraft depending on their routing for example at Vatsim UK places 2 minutes of time separation between aircraft departing on non-diverging SIDs and 1 minute between diverging SIDs. This is to prevent loss of separation incidents after departure. This creates the requirement for tower controllers to carefully choose the order of departures to maximise flow.