Boeing 747 Nose comes off when cargo door goes, usually. When the forward cargo door on Boeing 747s opens inadvertently several consequences can occur.
Door opens and minor consequences if plane is on ground.
Plane then crashes with total destruction and death. Engines stay on wing if shut down in time and plane lands if near airport. The door is eight feet by nine feet in size and outward opening, hinged on top. When it bulges out into the 300 knot slipstream just a few inches, or just a few degrees of its opening arc, the slipstream pushes against the door and flips it up and away tearing off fuselage skin and stringers with it. The amount of skin torn away is a minimum additional area of nine feet by ten feet.