Airports where airline demand exceeds the capability of the airport require a level of coordination to manage demand. Planned flight times are adjusted so demand remains within airline and passenger service level expectations.

Demand for flights at level 3 airport
Demand for flights coordinated to airport capability

Levels of Coordination

Airports are categorized according to the level of demand/supply imbalance. Different airport coordination principles and procedures apply at the different levels.

Level 1


  • The airport capability is generally adequate to meet demand.
  • No airport coordination is required at a Level 1 airport.

Level 2


  • An airport where there is potential for congestion during some periods of the day, week, or season.
  • Schedule adjustments are mutually agreed with the airlines.

Level 3


  • An airport where demand significantly exceeds the airport capability.
  • It is necessary for all airlines and other aircraft operators to have a slot allocated by an independent slot coordinator to arrive or depart at the airport.

Which airports are coordinated?

There are about 160+ Level 2 airports and 200+ Level 3 airports globally as published in the Contact list for Level 2 and Level 3 airports.

About 50% of all passengers depart from a Level 3 airport and around 35%  of all flights operate between two Level 3 airports. Airline scheduling is therefore highly complex, constrained by a lack of airport capacity, and reliant upon the standard airport procedures detailed in the Worldwide Airport Slot Guidelines (WASG).

How are airport slots allocated?

Airport slots are allocated by a coordinator according to industry agreed principles contained in the WASG. All coordinated airports complete the coordination process according to a Calendar of Coordination Activities. This facilitates a sequential allocation of slots at both ends of a route and across airline networks, ensuring efficient network connectivity and reliability of service.