Answer:
Oooh! (You have to be playing two player, or be beastly with jetpacks) Do the New Alexandria mission, and activate all of the beacons-or whatever. After you do that, find a giant ring in the middle of the city. Fly away and slightly to the left from a giant arch. Find a cool buildin with a couple radio antennas on the top and on the main level there is an overhang. On that building you can a) get the other player to jump on your falcon, then fly to the side AWAY from the arch and down. Under a certain overhang about halfway down, there is a button underneath it. Fly him/her up there, and have them activate it. Fly your falcon back and THROUGH THE TOP HALF A COUPLE TIMES IF THIS DOESNT WORK of the arch. Or you could b) find a jetpack and jump off the building. Get to the overhang and fly under it and into the buidling wall. There is a ledge all the way under it! Drop on that, and then fly up and activate the button. Fly back to the ledge and then jack a banshee that flies by. THIS TAKES TIME I RECOMMEND THE FIRST WAY! if you can't understand this look on YouTube. Also, you can fly a phantom this way but justness a banshee to fly through the arch! Tha is and have fun! Oh btw if you need a gunner for the pelican tell your friend to crouch and crawl around the right aide of you pelican holdin the action button. The pelican goes through buildings so have them stand on a building while you hover next to them. Have fun!