Airport slots: how take-off and landing rights are allocated at congested airports

What is a slot?

An airport slot is permission to use the full range of an airport's infrastructure to land or take off on a specific date and at a specific time. It is not an air traffic control clearance but a planning tool: it aims to match airline schedules with the airport's real capacity, whether runways, terminals or aircraft stands.

The mechanism is not used everywhere. It only applies at airports where demand persistently exceeds available capacity.

It should not be confused with an air traffic control "slot", allocated on the day when a sector of airspace is saturated and a flight has to delay its take-off. An airport slot is planned months in advance and determines whether a flight can be scheduled at all. An airline can therefore hold an airport slot and still suffer a delay imposed by air traffic control.

Three levels of airport

The worldwide reference framework is the Worldwide Airport Slot Guidelines (WASG), developed jointly by airlines, airports and coordinators and published by the International Air Transport Association (IATA), Airports Council International (ACI) and the Worldwide Airport Coordinators Group (WWACG). States are encouraged to apply them, but national or regional law prevails where it differs.

The guidelines classify airports by level of congestion. Level 2 airports are "schedules facilitated": timetables are adjusted through consultation. Level 3 airports, where demand exceeds capacity, are "coordinated": no scheduled movement can take place there without a slot. According to IATA, there are more than 200 Level 3 airports worldwide, handling around half of all passenger departures.

In Europe, a regulation since 1993

In the European Union, slot allocation is governed by Council Regulation (EEC) No 95/93 of 18 January 1993 on common rules for the allocation of slots at Community airports. The text, amended several times, requires in particular the appointment of an independent coordinator at each coordinated airport. In France, this task is entrusted to an association, COHOR.

The coordinator allocates slots for each scheduling season: summer and winter. It works from the airlines' requests and the capacity declared by the airport.

Historic precedence and the 80/20 rule

The most important principle is historic precedence, often called "grandfather rights". An airline that has operated a series of slots during a season may keep it for the equivalent season the following year, provided it has used it sufficiently.

This is the so-called "80/20" rule: according to IATA, an airline must operate at least 80% of a series of slots in a season to keep historic precedence. Below that, the series may be returned to the pool and reallocated. Certain unavoidable cancellations can count as operated. The principle encourages airlines to make real use of the slots they hold, but it is sometimes criticised because it can push carriers to keep running poorly filled flights rather than lose a valuable slot.

The slot pool and new entrants

Slots that are freed up, handed back or newly created by an increase in capacity go into a pool. The European regulation provides that part of this pool be allocated as a priority to "new entrants", meaning airlines with only a small presence at the airport, in order to encourage competition.

A major economic issue

At the most constrained airports, peak-hour slots are a strategic asset. They determine an airline's ability to offer connections, grow its network or withstand competition. That is why slots regularly feature in public debate, whether over airline mergers, divestments demanded by competition authorities or airport expansion projects.

Ahead of each season, airlines and coordinators meet at the slot conference organised by IATA to fine-tune their schedules.