It is pretty clear to me at this point that whatever caused the failure along the frame in the crown of the aircraft ahead of the rear doors was the primary cause of this accident. The direction of the line of failure is indicative that only the lower part of the structure was performing its function. The area of the initial line of failure is in a production joint. See attached picture of a new A321 tail assembly. The different primer colors highlight the different sections. (Source NYTimes.com article on new Airbus Mobile Alabama assembly plant)
The direction of tear is symmetric on both sides of the aircraft. See this picture from hamster3null. When you consider that aircraft are typically designed with a 50% safety factor above maximum load, it is surprising that the tear propagated as far as it did vertically before it turned forward.
If it was a fatigue failure, then there should be adequate evidence from the failed skin at the top of the rear fuselage section to make that determination.
(You do not have to have the opposite side of the failure to prove evidence of fatigue, the two sides will mirror each other.)
If it was entirely an instantaneous type failure from overstress, that also will be evident, in which case we will have a good case for an internally planted explosive device.
I suspect that electrical signals and hydraulics to the tail are routed along the crown of the aircraft. Can anyone verify this?
