About 1/3rd of the way through the "halo" level, there is a pit under the glowing bridge. This part is tricky - drive the warthog off the edge at a slant, so that the tip is pointed upwards. Try to land on the crooked ledge. If you fall off, try again. You have to stay in the warthog the whole time. You will end up in the pits.
Submitted by: Thor