Originally Posted by kraggy
Could anyone shed some light on how the slot-time system works from the point of view of the air traffic controller?
In simple terms:
The Central Flow management Computer in Brussels knows the theoretical capacity of every bit of airspace and every runway in Europe.
Say it states that a certain Sector can take 45 aircraft per hour at certain levels. However, 50 plan into it. 5 of those have to be shunted into the next hour to accomodate - hence a departure slot is issued to delay them.
The restriction is not just confined to area operations. For example - Airport has a major weather problem that reduces arrival rate, or loses a runway, or has staffing / equipment problems. They notify CFMU of the reduced acceptance rate - Flights inbound to the airport then get delayed so that the rate is adhered to.
Those are the "Slots" that you will see mentioned here. "Runway Slots" at major airports are a totally different game, and one way the major airports make their money.