Lidch, Hud and Ziga discover that its possible to get back into the pelican that initially drops you off at the start of assault on the control room. Many interesting places can be reached after that, and to our surprise its possible to flip the pelican as its flying causing it to crash into many walls and bump around. If you time it perfectly you will make it all the way down into the pit and walk around in a blue fog.
This trick was submitted via email on April 12, 2002.
Prior info: Tom posted a description of this trick on January 12, 2002 on the HBO Forum.