I do not believe this location has been submitted before. It has not been fixed. You can fly under Northrend from here:
1) Go to The Shadow Vault in Icecrown.
2) Head up over the mountains to the West. Look at my picture #1 below to find the location.
3) You'll want to swoop down behind the top of the bulwark up here. You can then go below Northrend - use this to get to the end of any cave you want without fighting through it, or just to explore. It's very useful.
4) Be careful because you can fall and die (lol)
5) If you do die in Icecrown, you can use the same exploit on your ghost mount and go wherever you like without fear of falling again.