The Metropolis level has a lot of cool stuff in it, but it's also a bit tricky. Get to the middle of the bridge where there is a hole in it that reveals the tunnel below. As soon as you get a checkpoint, get out and kill any passengers riding on your Scorpion, because if you don't they'll probably shoot down the Banshee you need. Kill one of the banshees but leave the other.

Hijack the remaining Banshee, dodge the Phantom's attack and shoot the three guns off. Right about now it'll start fleeing so chase it to the end of the highway. It'll start to lower a Wraith and this gives you a chance to jump out and onto the top of the Phantom. It'll carry you out of the level; the invisible wall won't effect you, as they only appear to affect Banshees.