First of all, the empennage is the rear of the airplane -- the tail assembly of an aircraft, including the horizontal and vertical stabilizers, elevators, and rudder. Now for this discussion, since the vertical stabilizer (the tail) detached from the airframe, the empennage is as above, but without the tail. The empennage was found on the ground at the crash site. What I have read tell me that the mounting flanges and bolts and nuts are all still in the empennage, nice and snug, thus the vertical stbilizer 'tore' off above its mounts. FReeper Zordas has info stating the the mounting flanges, nuts, bolts are inside the vertical stabilizer, still attached and snug, and thus the tail tore off inside the empennage. Either way, NO ONE is stating the nuts/bolts/flanges are the problem.
Now, folks are stating that composite materials are at issues, because that is the apparent failure point -- in fact a report from the crach site described the composite material in the empennage as looking like pieces of wheat straw (like the end of a broom) consistent with destructive failure of the material. That report is not (yet) in dispute.
So, what this establishes, so far, is that the vertical stabilizer appears to have separated from the airframe due to a strutural failure, not loose or faulty bolts.
NO RELIABLE source can state what caused the failure. We have enjoyed postulating on this thread. My own personal opinion is that the materials were close to fialure when the plane took off, and the airframe encountered fores that sheared off the tail, cleanly. It could have been wake turbulence. Maybe just the stress of flying was too much.
Once the aircraft lost the stabiliser, the tail, it departed controlled flight and crashed.
Now that you now what the empennage is, I think you can readily infer why it is important. A tall and big tail is important on swept wing jets to counter the effects of differential thrust (engines not pushing equally) and the resulting yaw, and because yaw (nose moving left or right relative to direction of flight) causes one wing to develop more lift than the other, and roll the airplane. The rudder 'straightens' the plane and evens out the roll. The tail is also just like the rudder on a boat. You can sterr an airplane with just the rudder, but that is called "un-coordinated" and can put the aircraft into what is called a skid (just like a car on ice).
Pardon the typos I 'm in a rush. Hope this helps.
If it was a force/bending action that cause failure of the material, there would have to be a bend line created to cause material failure, and that would have most likely occured at the bonding junction/edge of the doubler and the original material. When putting on the doubler, they would have had to sand a clean surface, possible fill the void with resin, apply resin to the original surface, apply the patch material, coat it again with resin, and possible form under vaccuum, (sealed bag in the immediate area) to prevent contamination, and use heat lamps to accelerate the curing cycle.
Of all the blades I personally tested, I never saw a doubler rip that I remember. I have seen skins rip, and quite quickly, too, but once bonded, all further rips or failures happened outside of the repair.
If this material tear is in the middle of the doubler section, then I would start talking about a bomb. Chances are, the doubler material is a different batch, maybe even a different manufacturer. At Kaman, we made the engine cowling for the CF-6 for GE, ailerons, flaps, stuff for the A-6, the original Osprey (AC #1), and blade skins for Sikorsky, too. I've seen lots of stuff go out the door that has held up quite well, and seen many repairs to blades and cowlings, too. To think that BOTH original material and doubler sections added for repairs failed at the same time, we are either talking about another COMET type design flaw or a bomb, or a stunt Airbuss A300!