the co-pilot, in trying to unlock the cockpit door for the captain who was returning from the toilet, mistook a command button for the cockpit door lock switch nearby.

Images from the flight recorder on the Boeing 737-700 showed the plane veered to the right and then sharply to the left, before dropping backwards. The aircraft tipped more than 130 degrees to the left at one point.

http://www.travelmole.com/stories/1149586.php?mpnlog=1

An object lesson in how not to do ergonomics and useability then, who thought;

“I know! Let’s put the ‘make the plane fly backwards button right next to the door lock!”

Genius.

[edit] poo, wrong forum.