According to several webpages, the NASA’s Boeing 747SP-21 is planning to make a visit this september:
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a refitted Boeing 747 SP with a 17-tonne telescope on board. Scientists often travel on board the aircraft, for example to observe young stars and planetary systems being formed or to study the Milky Way. SOFIA is coming to Stuttgart on September 15, 2019. It will be landing at Stuttgart Airport in the early hours of the morning, and flies back to its home base in California on Friday, September 20. – Unniversity of Stuttgart
At Stuttgart Airport, a special guest is expected on Sunday morning: The flying observatory SOFIA, a NASA Boeing 747SP, will be coming to Baden-Württemberg’s state capital on the occasion of an astronomy conference. – www.flugrevue.de
BUT! The site www.strforum.de says the plane arrival is delayed:
Wir haben soeben die Info bekommen, dass sich die Ankunft von SOFIA verspäten wird.
Sobald wir nähere Infos haben, geben wir es hier sofort bekannt.
We have just received the information that the arrival of SOFIA will be delayed.
As soon as we have more information, we will announce it here immediately.