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!