Flight Düsseldorf Airport departs from Dusseldorf Düsseldorf Airport at 09:40 and arrives at Belgrade Belgrade Nikola Tesla Airport at 11:40.
The flighttime is about 3h 00m. The distance travelled ("as the bird flies"): 1660 Km. So the average speed is roughly 553 Km.
There is an 1 hour time difference between Dusseldorf and Belgrade