Originally Posted by
bryancobb
Yep, I'm thinking the cabin roof maybe had its strength degraded over the years, possibly corrosion, possibly sheet metal repairs, possibly damage during engine removals/installs?
Not really. The roof itself is a honeycomb panel and is either serviceable or its not. The nodal beam assembly bolts through the roof panel to a separate roof beam attached to the underside of the roof panel. The footprint of that roof beam does not cover the entire roof panel and only covers approximately what is shown still attached in the photo above. The remaining roof panel on the fuselage can be seen in the NTSB pics. So while that set up works great in normal ops, the roof panel is not designed to take extreme lateral loads and will fail along the edges of the roof beam, if that makes sense. Unfortunately have seen this failure before but not in this manner while in flight.