Event contracts are a single handling contract that may be of a special airline livery or may just be a normal airline livery (which are available as contracts that can be purchased).
The events are mostly based on anniversaries or special events of those airlines or may even be random.
Events are released daily at 12:01 AM CEST (same as PRG time), though some events are released mid-day or in case of updates where the new/remodeled airports/aircraft liveries are released
The reward for the events are mostly the same (5 Experience Points and 10 Silver Planes) though in some cases you may get 1000 Silver Planes and rarely even a Gold Plane
The events which were available since 2.x.x have been listed month wise below, 1 month per post, the latest month would be on top with the rest in chronological order