OK, this probably only works on The Covenant on campaign and in Co Op, but it would be cool if you could try this in different ways on different levels and then submit it here.

Play through the level The Covenant (do not skip rally points!) and play through to the part when you get to the two scarabs.

Kill one scarab, all the Covenant and marines, but leave one scarab, or else the Pelican will fly away.

Now get one player on top of a Hornet (not in one!) and get the other to fly it.

Fly close to the hovering Pelican and fly close to it (but not so close you'll piss it off, like if you were attacking it) and have the player on top of the Hornet hold RB until he gets into the Pelican hangar and that's it.