the best way to complete this one on veteran is to simply do nothing. literally. try to never shoot people until after you blow the C4. avoid enemies at all costs. this will also get you the "ghost" achievement. if you get too close to a person and think he needs to be put down, just aim at him and McTavish will snipe him and rob your kill. the first time you should shoot is right after blowing the C4. you should only need to kill about 5 people right away as McTavish will take care of most of them. after that there is one area on the runway where you will have to kill about a dozen enemies. then its easy sailing to get to the snowmobiles and down the mountain. just dont crash