Ride in a Pelican
From Halopedia, the Halo wiki
Ride in a Pelican is a glitch that allows you to ride a Pelican on the Halo 2 level, Metropolis.
Walkthrough
When you come to the part of the level where there are two ramps and three Wraiths (depending on difficulty), destroy the Wraiths and all enemies. You should hit a checkpoint and then a Pelican will come to the bridge closest to the Marine building. Go up the stairs and as the Pelican is dropping off the Marines, jump up and to the left of the Pelican and hold X. You should now be riding the Pelican.
About a minute into the ride, you should reach your destination. You will be thrown from the Pelican and you should see it flipping uncontrollably. When you get close to it, it should say "Hold X to flip Banshee". If you press X, it will keep on flipping.
