>> i hit a massive rock. it got really weird. >> he takes off a second time but then -- >> i can't stand up without my knee flying sideways. >> reporter: john is a career stuntman in "ironman 3" and "transformers 3." surprisingly, this is his first injury. >> i'm not afraid of death. my mom blames me for all of her gray hairs. my wife is a mess every time i go on a trip. >> reporter: in a documentary on red bull tv, john faced that fear head on. stalling out on a ledge between two glacier crevasses. >> there is a fine balance of pushing too far. you will never know what is possible if you don't try the unknown. >> he is not about to let his bum knee hold us back. so he sends us up with his pal andy. back on top, the wind again a potential nemesis. without a lot of wind how will you fly? >> ski fast. >> reporter: and he does. >> woo!