Assuming this list is correct https://airport-city.fandom.com/de/wiki/Questreihen
2020
Above the clouds (13.02. - 26.02.2020)
On The Wings of Love (30.01. - 12.02.2020)
The dragon rises (16.01. - 29.01.2020)
Time to Rock (08.01. - 15.01.2020)
2019
The White Silence (12.12.2019 - 02.01.2020)
Pre-Christmas hustle and bustle (05.12. - 11.12.2019)
Thanksgiving (21.11. - 04.12.2019)
Airport City (06.11. - 20.11.2019)
Dark sky (October 17th - November 1st, 2019)
Comet's tail (07.10. - 15.10.2019)
The Curse of the Valley of the Kings (08/26/2019 - 09/09/2019)
Back to school (August 26th - September 8th, 2019)
The big game (12.08. - 25.08.2019)
Hot days (22.07. - 07.08.2019)
Cinemania (07/15 - 07/21/2019)
American week (01.07. - 14.07.2019)
Rock the sky! (June 18 - June 30, 2019)
Down to the rabbit hole (03.06. - 16.06.2019)
It came from outer space (13.05. - 02.06.2019)
Long-awaited post (29.04. - 12.05.2019)
Easter celebrations (April 15 - April 28, 2019)
Comet's tail (04.04. - 12.04.2019)
Spring is here (March 21 - April 3, 2019)
Dancing with the Leprechauns (March 11th - March 20th, 2019)
On The Wings of Love (25.02. - 10.03.2019)
Above the clouds (11.02. - 24.02.2019)
The dragon rises (28.01. - 10.02.2019)
Time to Rock (January 9th - January 17th, 2019)
2018
The White Silence (15.12.2018 - 05.01.2019)
Pre-Christmas hustle and bustle (03.12. - 10.12.2018)
Thanksgiving (11/15 - 11/29/2018)
The Curse of the Valley of the Kings (November 1 - November 14, 2018)
Dark sky (10/18 - 10/31/2018)
Down to the rabbit hole (04.10 - 17.10.2018)
Back to school (13.09. - 27.09.2018)
It came from outer space (23.08. - 12.09.2018)
Rock the sky! (July 16 - July 30, 2018)
American week (28.06. - 12.07.2018)
The big game (13.06. - 27.06.2018)
Long-awaited mail (28.05. - 11.06.2018)
Spring is here (May 7th - May 21st, 2018)
Hot days (April 17th - May 4th, 2018)
Easter cheer (March 27th - April 9th, 2018)
Dancing with the Leprechauns (March 7th - March 19th, 2018)
Above the clouds (13.02. - 25.02.2018)
Time to Rock (January 23 - January 28, 2018)
In 2018, there was a break (but there was no On the Wings of Love event). In 2019, no break. So anything still uncertain. Just wait for the developer
2020
Above the clouds (13.02. - 26.02.2020)
On The Wings of Love (30.01. - 12.02.2020)
The dragon rises (16.01. - 29.01.2020)
Time to Rock (08.01. - 15.01.2020)
2019
The White Silence (12.12.2019 - 02.01.2020)
Pre-Christmas hustle and bustle (05.12. - 11.12.2019)
Thanksgiving (21.11. - 04.12.2019)
Airport City (06.11. - 20.11.2019)
Dark sky (October 17th - November 1st, 2019)
Comet's tail (07.10. - 15.10.2019)
The Curse of the Valley of the Kings (08/26/2019 - 09/09/2019)
Back to school (August 26th - September 8th, 2019)
The big game (12.08. - 25.08.2019)
Hot days (22.07. - 07.08.2019)
Cinemania (07/15 - 07/21/2019)
American week (01.07. - 14.07.2019)
Rock the sky! (June 18 - June 30, 2019)
Down to the rabbit hole (03.06. - 16.06.2019)
It came from outer space (13.05. - 02.06.2019)
Long-awaited post (29.04. - 12.05.2019)
Easter celebrations (April 15 - April 28, 2019)
Comet's tail (04.04. - 12.04.2019)
Spring is here (March 21 - April 3, 2019)
Dancing with the Leprechauns (March 11th - March 20th, 2019)
On The Wings of Love (25.02. - 10.03.2019)
Above the clouds (11.02. - 24.02.2019)
The dragon rises (28.01. - 10.02.2019)
Time to Rock (January 9th - January 17th, 2019)
2018
The White Silence (15.12.2018 - 05.01.2019)
Pre-Christmas hustle and bustle (03.12. - 10.12.2018)
Thanksgiving (11/15 - 11/29/2018)
The Curse of the Valley of the Kings (November 1 - November 14, 2018)
Dark sky (10/18 - 10/31/2018)
Down to the rabbit hole (04.10 - 17.10.2018)
Back to school (13.09. - 27.09.2018)
It came from outer space (23.08. - 12.09.2018)
Rock the sky! (July 16 - July 30, 2018)
American week (28.06. - 12.07.2018)
The big game (13.06. - 27.06.2018)
Long-awaited mail (28.05. - 11.06.2018)
Spring is here (May 7th - May 21st, 2018)
Hot days (April 17th - May 4th, 2018)
Easter cheer (March 27th - April 9th, 2018)
Dancing with the Leprechauns (March 7th - March 19th, 2018)
Above the clouds (13.02. - 25.02.2018)
Time to Rock (January 23 - January 28, 2018)
In 2018, there was a break (but there was no On the Wings of Love event). In 2019, no break. So anything still uncertain. Just wait for the developer