His feet got caught in the flight controls, jamming the stick forward, turning off the autopilot, and forcing the plane into a dive and the sudden decompression pulled the cockpit door off it's hinges and onto the throttle controls so the copilot had no way of controlling the plane. Also the noise of the 550mph wind made it impossible to radio for help.
A flight attendant saw the captain hanging out the window and grabbed his legs. Eventually they got the debris off the controls and untangled his legs and the copilot brought the plane down to 12000 feet where they could breath but he cautioned the attendant to continue to hold on to the captain's legs because he didn't want him to release the body and have to fly into an engine.
At the lower altitude captains body slide down over the side and his face was smacking into the side windows leaving a smear of blood over everything.
The attendant holding his legs eventually had to switch places with another because all the skin on his arm was burned off from the cold and high wind shear. They flew another 30 minutes before the copilot could land the plane.
When they reached the ground they discovered the captain was somehow still alive.
You can skip through a terrible re-enacted documentary here (or here). Some of these pictures are re-created and some are real.