Landing slots are allocated in accordance with guidelines set down by the International Air Transport Association (IATA) Worldwide Airport Slots Group. All airports worldwide are categorized as either Level 1 (Non-Coordinated Airport), Level 2 (Schedules Facilitated Airport), or Level 3 (Coordinated Airport). At Level 2 airports, the principles governing slot allocation are less stringent; airlines periodically submit proposed schedules to the administrating authority, rather than historic performance.