The Great Banshee Switch
From Halopedia, the Halo wiki
It is possible to have 2 players in separate Banshees, and actually trade Banshees in mid-air! This stunt requires great skill, timing, and sometimes just pure luck. (which is exactly how I did it) First, both players must be flying in the same direction, and at the same speed. The first player must position his Banshee directly above the second, and just a few centimeters forward. At this point, the Banshees should be touching. Now, both players must get out at the same time, and when they are close enough, they must press X to get in the other player's Banshee. If done correctly, you will switch Banshees in mid-air!