When you are in the Ark mission after the destroyed phantom there will be a fork in the road.

Take the right side and you will see a platform with nothing on it.

You will want to get a brute chopper and go to the spot were the LZ is, but don't go through the cave.

Instead stand in front of the cave and don't get a checkpoint, take your chopper and go up on the big long rock you are looking at when you stand in front of the cave.

Take the chopper and ride on the rim of those rocks.

When you get to the edge of the platform, it might take a few tries, but you have to hit the boost button and you will propel up on the platform.

Trust me its a lot easier than having to find a small curve!