On the final level "Great Journey", you will have to fly the banshee. You are told to enter the door in the huge structure. Fly up to the door and exit the banshee, make your way through the tight cave like hallways and open the door. Kill the brutes in this room, make sure you kill them all, do not use the banshee, they have brute shot and are good with plasma grenades.
After clearing the room, go back to your banshee and fly through the door, immediately start flying up, and you will notice a hole, fly through it. Continue flying through the holes you see and down through the door. Make your way to the right side of the room and down the long hallway (while in the banshee). A cut scene will take you out of your banshee to where the chieftain and 4 or 5 brutes are standing, after you kill them and the chieftain jumps to the center, make a 180 back to the hallway and get in the banshee.
Fly in circles around him, blasting him with all the banshee weapons. After a while, when his shields go down, you will have to land your banshee on the bottom level and engage the chieftain, shooting him, just pissing him off. When the brute reinforcements come, get back in the banshee and continue to bomb them and the chieftain until you are victorious.
NOTE: if you have trouble at any point, for example, if it seems it is taking forever to kill the chieftain, jump out of the banshee and engage him for a few minutes, just don't get killed (but if you do, your banshee will be waiting in the same spot you got it from) after a moment of fighting him on foot, jump back in it and continue, eventually he will die and you will be a lot safer in the air then down on his level.