Main Story - Can't advance?

[Enkidoh]

When you first arrived in the Blue Window (the area in the Sea of Clouds you have to go to for the quest), Wedge should have mentioned that he's established a 'Garlond Ironworks airship route' to that location, shown by a Ironworks Standard flag at the location, which he said you could use to hail an airship that could take you back to Ishgard quickly if you needed it.

This also works in reverse, in that there should now also be a Garlond Ironworks npc at the Airship Dock who will fly you back to the Blue Window (I can't remember the name or location of this npc sadly). Either way, try talking to every npc at the Airship Dock, as one of them should be able to fly you where you need to go (it's the Blue Window in the Sea of Clouds that is the destination you need).