OK, since there's been an argument in my last post"Pelican Down" about it being impossible to bring the pelican down on the Siera 117 level of campaign...
Ok, firstly you need to stand where I am to make it easier.

Next, there is a certain target area. You can only throw it there, because that's the only area the plasma nade will go through. Anywhere else it'll merely stick onto the outside to.
NOTE: The nade will only go through in SOME spots in the target area.

This would be an example of a miss.

Now, here's a way to tell if you have killed the pelican. There IS a driver, not some sentient AI crap. If you see someone fly out from the explosion, that means the pelican will be coming down. But watchout though, because there's also a turret man in the back so you might just be killing him :S.