Airport slots are specific scheduled times allocated for an airline to take off or land at an airport where demand exceeds available capacity.
These slots are coordinated in advance of each scheduling season, the Northern Summer and Northern Winter, following a global calendar of coordination activities. Some jurisdictions complement this calendar with additional coordination meetings held closer to the start of the season. This process helps maintain operational efficiency and reliability at airports facing high demand.
While often associated with major hub airports, slot management may be necessary at airports of any size, depending on the level of congestion. To reflect varying degrees of congestion, airports are designated under different coordination levels.
Levels of Coordination
The level of coordination should be decided based on the results of a thorough demand and capacity assessment.
Level 1: Non-Coordinated Airports
Level 2: Schedules Facilitated Airports
Level 3: Slot Coordinated Airports
Capacity Declarations
At Level 2 and Level 3 airports, “coordination parameters” define the maximum capacity available for allocation, taking into account infrastructure, operational and environmental limitations such as runway capacity, aircraft parking stand availability, terminal throughput, airspace capacity and noise restrictions. These parameters are defined in the capacity declaration for each scheduling season.
Airport operators should lead the capacity declaration process, given their responsibility for developing and managing airport infrastructure. Where regulators are formally responsible for declarations, they should rely on the airport operator’s expertise.
ACI has developed guidance to support Level 2 and 3 airport operators in conducting capacity assessments and capacity declarations as part of the coordination process.
The Worldwide Airport Slot Guidelines (WASG)
Jointly published by ACI, IATA and WWACG, the Worldwide Airport Slot Guidelines (WASG) provide a global framework for managing scarce airport capacity through slot coordination and schedule facilitation.
Originally developed by the airline industry in the 1970s, the WASG reflects the conditions of a more regulated air transport market. Over the years, air traffic has grown, airline business models have diversified, and airports have evolved in ownership and structure. While the WASG has undergone multiple revisions, its foundational principles have not kept pace with the broader structural changes in the aviation sector.
As aviation is a global industry, a globally compatible process is essential to ensuring predictability and consistency across markets. Representing industry best practice, specific provisions of the WASG have, to varying degrees, been adapted by some regulators or airport operators to reflect local needs and circumstances. ACI World, in collaboration with the ACI Regions, supports this process by engaging with regulators and airport stakeholders to ensure that slot policy remains responsive to regional and local operational realities.
ACI World’s Role in Slot Policy
ACI World formally joined the governance of the global slot system in 2020 through the establishment of the Worldwide Airport Slot Board (WASB), alongside IATA and WWACG. The WASB is responsible for publishing the WASG and provides a formal mechanism for airports to contribute to its ongoing development.
While this structure offers a platform for collaboration, progress toward more balanced outcomes has been limited. As demand for air travel continues to grow, ACI World, in collaboration with the ACI Regions, continues to engage within the WASB and with regulators to ensure that slot policy evolves to support connectivity, competition and sustainable growth in the public interest.
The Expert Group on Slots (EGS)
The ACI World Expert Group on Slots provides strategic and technical guidance to ACI World on airport slot allocation policy. It also supports the WASB airport representatives by contributing input used in joint discussions with airlines and slot coordinators on the interpretation and future development of the WASG.
The group includes members from all ACI Regions to ensure local circumstances and operational realities are reflected in ACI World’s slot policy positions.
Learn More
Explore ACI’s resources on slot policy and opportunities for ongoing improvements:
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Questions about ACI’s work on slots?
Contact us at slots@aci.aero.