I need help with we're in for some chop

If you do the 3rd mission, on the bit where the chopper crashes into the warthog there are 2 bunkers. One of them has some trip mines in which you can use on the other choppers.

Ok this is how I got the acheviment on Tavso High (easyist setting) way were the enemy ship comes down and drop off that wraith. Their are some trip mines in the the back near the building grab them and go to the next area were all the brutes are on the choppers damage it first because it wont destroy it with one mine. After it is damage drop the mine in front of it. If you don't get it the first time you can always go back to the last check point.

Okay, go to campaign mode and choose Tsavo Highway. Play through the level until you get to the part where the chopper crashes through a warthog. Don't kill the choppers!! Go into the bunkers/houses and inside one of the bunkers on the right will be a coupler of trip mines. Get a trip mine and kill the brute(s) and the grunts that are next to the sea land container, once you killed them go to the right side on the container and toss a trip mine into the center of the road. There are 2 or 3 trip mines in the bunker, so if it doesn't work the first time just try again=)

Ps I think it works best on Heroic or Legendary.

You have to destroy a chopper with a trip mine.

Destroy the chopper with the trip mine.