The coordination process between airlines and airport coordinators is described in the IATA Worldwide Scheduling Guidelines (WSG) which contains a set of procedures and time frames to provide guidance for the management of the allocation of scarce resources at busy airports.
The communication between airlines and coordinators is outlined in the IATA Standard Schedules Information Manual (SSIM) which is constituted under IATA Passenger Services Conference Recommended Practice 1761b that was declared effective July 1, 1972. Standard message formats have been agreed to allow airlines, airport coordinators and schedule facilitators to exchange airport coordination and schedule movement information electronically. The message formats are integrated into an iterative (sequential) set of request and reply messages and have been designed to provide as much clarity as possible for the message users. The received message details can be processed either by computer or by manual methods. The rules for the use and composition of the messages, together with detailed specifications and examples, are explained in chapter 6 of the SSIM.
Historical precedence ("grandfather rights")
The core of the slot allocation process is the use of historical precedence. This precedence applies only to equivalent, and not consecutive, schedules seasons (e.g. Summer to Summer season) and is limited to the equivalent period and days of operation. This principle entitles an airline to claim a series of slots within the same coordination parameter(s) in the next equivalent schedules season, provided that (for more details please consult Definition of series and determination of historic rights guideline):
the slots were allocated for regular scheduled services forming a series of slots
at least 80% of the slots were operated by an airline as cleared by the coordinator.
Submission for new season
About six month before the start of the respective schedules season, airlines provide coordinators with their schedule clearance requests for the arrival and departure times required at the airports concerned. The submission is sent by email as a defined standard message format, called SCR (Slot Clearance Request).
Initial coordination (seasonal planning)
The coordinator collates this information and identifies periods in which slot requests exceed declared airport capacities. Slots are allocated according to the recommendations of the IATA Worldwide Scheduling Guidelines and in Europe, according to the respective EEC95/93 Regulation and amendments. All airlines are informed by email about their allocated slots prior to the start of the upcoming schedules conference.
IATA schedules conferences
Schedules Conferences are held twice each year (June and November) about five months before the start of the respective schedules seasons and are organised by IATA. The conference represents approximately 120 worldwide coordinated airports and 250 airlines and will be attended by about 800 delegates in total. During the 4 days conference, schedules are adjusted mainly through bilateral meetings between airlines and coordinators regarding alternatives offered, or between airlines to exchange slots offered or accepted. A schedule change at one airport must affect one or more other airports. Because all coordinators attend the conference, it provides the best forum in which all such repercussive changes can be quickly and efficiently processed, and airlines can leave the conference with firm schedules which they consider are the best compromise between what is wanted and what is available. The entire process is based on consensus and aims to be flexible, fair and open.
Slot handback deadline
Airlines must not hold slots which they do not intend to operate, transfer or exchange, as this could prevent other airlines from obtaining slots. If an airline becomes aware that for whatever reason it may not be able to use a slot, or series of slots, the airline must advise the coordinator, and handback any slots it knows it will not use. Unwanted slots must be returned no later than January 15 for the next Northern Summer season and no later than August 15 for the next Northern Winter season.