Process of coordination

The calendar year is divided into two scheduling seasons

Summer season from the last Sunday in March to the last Saturday the following October
(where the following Sunday is still in October)
30-31 weeks
Winter season from the last Sunday in October to the last Saturday the following March
(where the following Sunday is still in March)
21-22 weeks

The process of coordination is driven by a calendar of activities.
Before the season:

Capacity Determination
Allocation of historical slots to individual carriers
SHL-deadline (Slot Historical and Non-Historical Allocation List)
3rd Monday in April (SHL out of last winter for next winter-season)
3rd Monday in September (SHL of current summer for next summer-season)
Take stock of initial slot requests for next season
Submission deadline
middle of May (for next winter-season)
middle of October (for next summer-season)
Initial Slot Allocation
SAL-deadline (14 days prior to start of IATA Schedule Conference sending out the result of the initial slot allocation to the individual carriers)
IATA Scheduling Conference
in June (for next winter-season)
in November (for next summer-season)
Long-term coordination
Additional slot requests and changes to already coordinated slots
(principle of first come, first served)
Waitlist handling
Slot Return Deadline
15JAN for summer-season
15AUG for winter-season
Historics Baseline Date
31JAN for summer-season
31AUG for winter-season
31JAN and 31AUG is also the start of use-it-or-lose-it (80/20) calculation
Waitlist handling
Begin of ad hoc slot request handling and ad hoc changes
Begin of scheduling season

During the season: