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http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/LaudaAir/LaudaRPT.html#2.2.3

2.2.2 In-Flight Breakup Sequence

The analysis of the major structural damage showed that the failures were probably the result of buffeting, maneuvering overload, and excessive speed. Parts of the airplane that separated from buffeting overload appear to be pieces of the rudder and the left elevator. This was followed by the down-and- aft separation

19 of most of the right horizontal stabilizer from maneuvering overloads, as the crew attempted to control the airplane and arrest the high-speed descent. No evidence of impacts were observed on the leading edges of the horizontal and vertical stabilizers indicating that no airframe structural failure occurred prior to horizontal stabilizer separation. It is thought that the download still present on the left stabilizer and the imbalance in the empennage from the loss of the right stabilizer introduced counterclockwise (aft looking forward orientation) torsional overload into the tail, as evidenced by wrinkles that remained visible in the stabilizer center section rear spar. The separation of the vertical and left horizontal stabilizers then occurred, although the evidence was inconclusive as to whether the vertical stabilizer separated prior to or because of the separation of the left stabilizer and center section. (The damage indicated that the vertical stabilizer and the attached upper portion of four fuselage frames departed to the left and that separation of the vertical fin-tip and the dual-sided stringer buckling in the area of the fin-tip failure occurred from bending in both directions prior to the separation of the vertical stabilizer from the fuselage).

I don't understand. The tailcone is already designed to take torsion from the much larger tailfin. And we know that A587's tailfin snapped off rather than twisting the entire tailcone off. So how can a tailplane cause so much stress rather than snapping off?

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In most of these airplanes the vertical fin is attached to lugs along the upper skin and frame structure and to the bulkheads at the front and rear spars of the fin. Overloads will tend to break the structure at the interface of the fin and fuselage, the weakest point when subjected to bending loads.

The horizontal tail is quite different. It's normally a one-piece torsion box very similar to the main wing, whose primary structural connection is a massive hinge joint within the tail cone structure at the rear, and a jack screw attachment at the front. The result is torsional overloads of the horizontal tail will tend to brake apart the structure inside the tail cone itself rather than the horizontal stabilizer box or its hinge lugs, whereas the fin tends to want to break where it's attached at the skin/fin interface.

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