Since 1947, under the auspices of IATA, airlines have met regularly to discuss schedules planned for the following season, in order to improve interline connections and handling arrangements.
Primarily through bilateral discussions, they voluntarily adjusted their schedules where it was in their mutual interest to do so. Their main objective was to return home with firm schedules which triggered the various preparations that were needed to operate them – in purchasing, staffing budgeting and selling.
With the onset of congestion during some periods of the day at a few major airports in the early 1960s, the scope of the schedule discussions was broadened to cover the adjustments needed to reduce anticipated delays to an acceptable level.
In instances where airport services that were planned during certain periods exceeded what the airport could accommodate without unacceptable delays, some services would have to be moved, usually with some economic penalty. Over the years, a consensus developed as to which services should be moved, in fairness to all those who were planning to operate during the period.
The recommended procedures and priorities for such schedule adjustments are contained in the IATA Worldwide Scheduling Guidelines. Editions are regularly issued in response to changing circumstances, after endorsement by all airlines attending the scheduling meetings.