Savegame with the bug: http://www.lorion.de/temp/savegame17.dsg

The bug seems to occure when you've picked up some zeppelinparts before you actually started the quest. Tried it with another savegame where I just got the dragontower. Flew right to the port, started the quest and picked up one of each of the parts, gave them to Petzold and Sepp would let me fly to Aleroth.

Would be great if you could release a console command so that people with bugged savegames can set the "quest finished"-flag themselves and continue playing with their savegame cause in my case the bug means 10+ hours of playtime I had to do again (and I am probably not the only one).