I forgot to mention earlier - I think you can ride the Zeppelin before you turn in *all* the parts. Have you tried just talking to the guy on the ramp?
As for the barrier. . . guess I'm confused. Which barrier are you referring to? Are you talking about the very large force field that covers the entire Harbor, and the second large forcefield which covers the Slayer training camp? I don't think you can lower those shields. You can fly around them however - the forcefield doesn't completely block your flight through the fjords.
