From version 3.3
Weekend events
One airport and one twist, every weekend, from version 3.3.
Weekend and holiday events
Every weekend one of the 50 busiest airports gets its own twist. Holiday events are planned for version 3.4 of the game.
Coming in version 3.4
Thanksgiving Rush
One of the busiest travel weeks of the year in the United States, planned for version 3.4.
Coming in version 3.4
Santa
A Christmas Eve event, planned for version 3.4.