Excatly what do I have to do in the engineering section after I hit those 4 switches on the 3rd floor?

You gotta shoot your rockets or toss a grenade into the area exposed when those tube like things slide back. If youre not sure where they are just drop down on top of one after you pull the switch and look down the length of the tube.

The easiest thing to do is once you hit the button, turn around, drop off the edge of the platform onto the top of the pipe, then crouch and drop into the mouth. Toss a grenade into the pipe when it looks red and isn't be blocked, then drop off before the pipe closes again.

Do this x4 then exit via the top right door -- on the pipe level.

Tuan Jim

I found using the rocket launcher was much easier than the grenades.

could be, I wasn't sure how far they'd go in before exploding and the launcher can do a lot of damage.

Plus, I wasn't carrying around the launcher at that point due to lack of ammo, and inconvenience in Normal diff. I suppose in Legendary there could be flood using the launcher in that room.

Tuan Jim

If you do the trick were talking about with dropping onto the tubes youll be right up on those bad boys you can use whichever you have more of, cant miss either way. I would rather waste the rockets cause the grenades are better for the Flood and Covenant.