Worldwide Airport Slots

An airport slot is permission for an airline to arrive at or depart from a specific airport at a particular time. Slots are used only at highly congested, or Level 3, airports where demand exceeds the capacity of runways, terminals, gates, stands, or airspace.

A slot is not the same as a route right, landing permission, or gate allocation; an airline must still meet all other operational and regulatory requirements. Slots are normally allocated as a series for a scheduling season, enabling airlines to plan and publish reliable timetables. By matching planned flights with the airport capacity available at different times of day, slots help make scarce infrastructure usable and predictable.

Most airports do not need slots because they have enough capacity for airlines to schedule flights freely. Slots become necessary when airlines want to operate more flights at particular times than an airport can safely and reliably handle. Without coordination, too many flights could be scheduled for the available runways, terminals, gates, stands, or airspace, causing congestion, delays, and disruption.

Slot coordination matches airline schedules with the capacity the airport can realistically deliver. This supports more reliable operations, makes efficient use of scarce infrastructure, and gives airlines and passengers greater certainty. Formal slot coordination should be introduced only after a thorough demand-and-capacity analysis, stakeholder consultation, and a decision by the authority responsible.

At a fully coordinated airport, slots should be allocated by an independent slot coordinator—not by the airport, government, or airlines themselves. The coordinator applies the relevant law and the Worldwide Airport Slot Guidelines in a neutral, transparent, and non-discriminatory way.

Allocation starts with the capacity declared by the airport or competent authority. The coordinator then considers historic precedence, requests from new entrants and existing airlines, operational feasibility, and agreed allocation priorities. Airports, airlines, and other stakeholders may discuss capacity and coordination issues through local committees, but they do not decide individual allocations. Independence is essential so that no interested party can improperly influence access to scarce airport capacity.

No. A slot is a permission to use airport capacity at a particular time, not ownership of part of the airport. An airline may gain historic precedence to continue using a series of slots in the next equivalent season if it meets the applicable rules, including the 80% utilization requirement. This continuity is important because airlines plan aircraft, crews, networks, and ticket sales many months ahead. However, historic precedence remains conditional.

Slots that are not sufficiently used may return to the pool for reallocation, and airlines should promptly return slots they do not intend to operate.  

The 80/20 rule means that an airline must operate a series of slots at least 80% of the time during a scheduling season to retain historic precedence for the next equivalent season. If the airline falls below 80%, the series may return to the slot pool and be allocated to another airline.

The rule encourages efficient use of scarce capacity while allowing limited flexibility for cancellations, operational disruption, and changes in demand. It does not mean airlines routinely cancel 20% of flights. Certain cancellations caused by unforeseeable and unavoidable events outside an airline’s control may qualify as justified non-utilization and be treated as operated for this calculation.

New airlines apply to the independent coordinator for slots. Requests are assessed against the airport’s declared capacity and the allocation priorities in the Worldwide Airport Slot Guidelines. After airlines with historic precedence have been considered, unused, returned, or newly created slots enter the slot pool. New entrants receive priority for at least 50% of the slots available in that pool, provided their requests can be accommodated. The remaining slots may be allocated to other applicants.

At the most congested airports, there may be few suitable slots available at the requested times, so a new airline may be offered different times or remain on a waiting list. Once allocated, new entrants can also earn historic precedence by meeting the same utilization rules as other airlines.

The Worldwide Airport Slot Guidelines (WASG) provides the globally accepted framework for managing airline schedules at congested airports. It sets common principles and processes for declaring airport capacity, requesting and allocating slots, earning historic precedence, returning unused capacity, monitoring performance, and resolving coordination issues.

The WASG is jointly developed by airlines, airports, and slot coordinators through the Worldwide Airport Slot Board and is jointly published by IATA, Airports Council International, and the Worldwide Airport Coordinators Group. The aim is to allocate scarce capacity fairly, transparently, consistently, and without discrimination while supporting connectivity, competition, reliable schedules, and efficient airport use. We encourage governments to incorporate the WASG into national rules; but where national law differs, that law takes precedence.

At busy airports, the limiting factor is physical or operational capacity. Runways can handle only a safe number of movements; terminals, gates, aircraft stands, baggage systems, security facilities, and surrounding airspace also have limits. Demand is often concentrated at the most attractive times of day, when business connections and passenger preferences are strongest. If all requested flights were added, the result would be congestion, delays, missed connections, and unreliable schedules.

Slot coordination can distribute the capacity that exists, but it cannot create more capacity. Airlines may add flights only when suitable slots become available through returns, new capacity, schedule changes, or reallocations from the slot pool.

The fundamental solution is to increase usable airport capacity where demand justifies it. This may involve new or improved runways, terminals, gates, stands, taxiways, airspace design, technology, staffing, or operating procedures. Airports should regularly review declared capacity with airlines and coordinators so that every safe, operationally deliverable opportunity is made available.

In the meantime, independent coordination, timely returns of unused slots, the 80/20 rule, monitoring, and priority for new entrants help use existing capacity efficiently. Larger aircraft can carry more passengers with the same number of movements, but they do not meet every market need. Auctions or higher charges may redistribute access, but they do not create additional capacity and can increase costs and uncertainty.

No. Slot coordination should remain focused on allocating scarce airport capacity fairly, transparently, consistently, and without discrimination. Using aircraft emissions or an airline’s environmental performance to decide slot access could fragment the global system, reduce connectivity, disadvantage some routes or business models, and create complex comparisons that change as fleets and operations evolve.

Aviation CO₂ emissions are better addressed directly through sustainable aviation fuel, more efficient aircraft and operations, improved air traffic management, and effective global climate initiatives such as CORSIA. Slot coordination can still contribute indirectly by reducing congestion and supporting reliable operations, but it should not replace dedicated environmental measures. Where noise or other local impacts require action, authorities should assess proportionate options through established frameworks such as ICAO’s Balanced Approach.

Yes. The current system provides a stable, transparent, and globally consistent way to manage scarce capacity at congested airports. It supports high levels of airport utilization, reliable schedules, connectivity, and access for both established and new airlines. Common global rules are particularly important because airline networks depend on coordinated timings at airports in different countries.

However, the system can work well only when all parties apply the Worldwide Airport Slot Guidelines consistently. Airports must declare realistic capacity, coordinators must be independent and transparent, and airlines must use or promptly return their slots. The WASG is regularly reviewed and updated by airlines, airports, and coordinators (with over 30 editions since 2000), allowing the framework to adapt while retaining the certainty needed for long-term planning.