Having just watched the video footage of the accident, I can now understand how witnesses described the aircraft cartwheeling and am thoroughly astounded that there were not significantly more casualties. It is enormous testament to the quality of design that the fuselage stayed relatively intact following that sequence. The footage actually looks very similar to the crash sequence/progression at Sioux City, (obviously a far lower speed less inertia and different attitude at first impact) With regards to cause, I do not wish to, nor am I qualified to speculate, the NTSB will, in their own time provide us with a full sequence of events that led to a broken aircraft and sadly lives lost.