Single European Sky (SES)
A concept by the European Commission to restructure the European airspace and air navigation service providers.

There are two types of slots: In air navigation services, a slot is an allocated time window during which a departure or landing must be performed or a fix must be overflown. Slot allocation is used to manage traffic flows and enhance punctuality.

They have to be distinguished from airport slots: Airport slots are negotiated between airports and airlines and lay down the landing and departure rights at the relevant airport.

Air traffic controllers guide aircraft in such a way as to ensure that defined minimum distances between two aircraft are not infringed: vertically at least 1,000 ft and horizontally between 2.5 and 6 NM.

Short-term conflict alert (STCA)
The short-term conflict alert (STCA) system assists the controller in maintaining separation between two aircraft by generating, in a timely manner, an alert of a potential infringement of separation mininma.