Perpendicular Banshee fire
From Halopedia, the Halo wiki
To see the 90 Degree Banshee Fire, you must have Halo: Combat Evolved. Turn the Banshee such that it only goes straight up. Then fire a Fuel Rod shot. Notice that the shot goes perpendicular to the direction your Banshee is going, not forward like it usually does.
Walkthrough
On the level Two Betrayals when you hop into the Banshee fly back into the control room. Nose-dive into the large pit until you hit the bottom. Then get the Banshee to look directly up, when you start flying upward your fire should go to the side. When you get out of the pit however it will stop and will fire normally.
