Hi Rasmussen,
Thank you very much for the information about Artur Gross´flights. 
The following source indicates that Gardelegen was handed over to Allied forces on 14 April 1945: 
http://www.gardelegen.info/cms/index.php?article_id=98
Gross landed on 17 April 1945 at Gardelegen airfield even though Gardelegen itself was captured by the Allieds already on the 14 April. Maybe the airfield was far away from the town and not yet captured? Do you know when the airfield was captured by the Allieds?
Best regards,
Roger