Source: Tariffs for Airports and Air Navigation Services (Doc 7100) – 2004 Edition
b) Schedule coordination and slot allocation
4.5.2.2 As the problem of airport traffic peaking and congestion is very complex and difficult to solve to the satisfaction of all parties involved, the different measures to deal with it have evolved. Over a long period of time, the International Air Transport Association (IATA) has developed a process for schedules coordination and slot allocation through the IATA Schedule Coordination Conferences. At these conferences, which are held bi-annually, IATA and non-IATA airlines coordinate their planned seasonal schedules with respect to declared airport capacity limitations. Schedule coordination may include, where necessary and agreed by those involved, slot allocation. The latter is a mechanism whereby a certain period of time (usually 15-30 minutes) is allocated by a coordinator on a designated day for an aircraft to arrive at or depart from an airport.
4.5.2.3 To reflect different degrees of capacity constraints, the IATA schedule coordinating procedures have two different levels for resolving scheduling difficulties at an airport. Airports which are designated as “schedules facilitated” are those where demand is approaching capacity and where voluntary cooperation in adjusting schedules can be used to resolve, for example, the problem of an emerging shortage of slots at certain periods during the day. Airports which are designated as “fully coordinated” are those where demand exceeds capacity, with no possibilities of resolving the problem in the short term (e.g. through opening a new runway or terminal), and formal procedures are used to coordinate schedules. Where there are seasonal capacity constraints, both these designations can be used with airports being fully coordinated in the summer period and with schedules facilitated in the winter period.
4.5.2.4 The fully coordinated airports tend to be concentrated in Europe. One major factor contributing to this is the impetus given by the introduction of the 1993 European Union common rules on slot allocation which led to many additional airports being designated as such by national administrations, and hence in the IATA system. There have also been increases in fully coordinated airports in other regions, particularly in Asia/Pacific, reflecting strong traffic growth in that region.
4.5.2.5 Airports can be fully coordinated because of year-round traffic peaking during certain times of the day. In such cases, there is some additional capacity available in terms of unused slots, although this may be at odd hours. Another means of assessing the global trends in capacity constraints using fully coordinated airports is to look at the increase in aircraft movements and passenger traffic at those airports.
4.5.2.6 An airport slot should not be confused with an air traffic control (ATC) slot, the take-off or landing time of an aircraft which is assigned by the relevant ATC authority to make optimum use of available capacity at points en route or at the destination airport by sequencing the air traffic to regulate its flow efficiently. Thus, commercially operated aircraft may not land or take off in the same order as reflected in their respective schedules, but at times which would enable air traffic control to regulate efficiently the flow of aircraft into or out of the airport and the en route system. This may involve, for example, interspersing commercial flights with general aviation flights and varying the order of take-off or landing to take account of greater separation requirements for larger aircraft, late arriving aircraft, etc. This underlies the importance of close coordination between the coordinator assigning the airport slots and the air traffic control authorities.
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