The term monocoque, which means “single shell,” properly denotes structures that have no internal framing whatsoever. A tip tank, for instance, might be a pure monocoque: Its outer shell carries all the weight of the fuel, without any internal spine or frame other than whatever local reinforcement is required for attachment to the wing. A fuselage could be a pure monocoque, but large cutouts for doors and windows, and hard points for attaching wings and engines, require local reinforcements that begin to look something like a partial frame. Consider, for instance, the fuselage of a Cessna Skyhawk. Open the doors, and there appears to be almost nothing between the tail cone and the engine. All the loads pass through the floor, the ceiling and the windshield posts. Strong built-up sections surround and reinforce the door and window openings. From the point of view of crashworthiness, there is no reason these bent and stamped aluminum angles, channels and box beams should be inferior to a welded-steel frame.