@bearfoil
...my strong conviction that the Vertical Stabilizer and Rudder were not on the fuselage at impact...
To add to the many suggestions attempting to answer your question regarding how the VS became detached, it is worth considering just how water impacts vary from those on hard terrain. During impacts with rigid ground the undercarriage, if deployed, absorbs a significant portion of the impact energy, with the remainder being transferred to the stiffest structural members such as the energy absorbing subfloor beams. These are generally designed to progressively collapse in order to limit to G load on the occupants. For a water impact, the loading mechanisms differ significantly. The landing gear is unable to absorb the impact energy and instead the impact loads are distributed as a transient dynamic pressure load over the fuselage skin. This initial absorption by the skin momentarily slows the rate that force is applied to the structural members, and has the effect of inhibiting the buckling process to the extent that energy absorbing subfloor components become ineffective. This is why in recent years Navy helicopters have been designed with additional features to improve their crashworthy response over both hard terrain and water.
If the skin is compromised, and the fluid is uncontained, as is the case with a high velocity impact, constant interactions occur between fluid and structure, inducing continuous changes in the loads applied throughout the crash event. In addition to the previous mechanism, the structure now experiences considerable hydraulic shock allowing large pressure forces to act directly upon the cabin floor and interior and as a consequence, increases the vertical accelerations experienced by the occupants.
Drop tests on passenger sized airframes at NASA Langley Research Center have shown how the cabin section experiences quite a pronounced deformation even for a 10m/s drop. For the impact suffered by AF447, which likely descended at a rate in the region (60 to 80m/s), the deformation would have looked more like that for the Trident accident (Papa India in 1972), where the appearance of the main cabin sections are very much more flattened . Given the likely fuselage distortion under AF447's VS, even with the rear bulkhead support, the tendency will be for the fixings under the VS to suffer serious deformation and fracture. Now, some milliseconds later, add hydraulic shock imparted by HP water meeting the underside of the cabin roof, and one can easily imagine how the downward movement of the upper cabin shell is arrested, while at the same time, the inertia of the VS imposes itself on the support fixings with the resulting failure and separation. The evidence for significant hydraulic damage is apparent in the photo of the fuselage/door section where the inner lining has been scoured away.
What happened next to the VS is open to some conjecture. It has been suggested that the VS flipped forward over the airframe and splashed down in front of the aircraft. I find this scenario less than convincing since that pathology report gives no indication of any forward injuries, which would suggest minimal forward motion. If the VS had just fallen over onto the airframe, then surely there should have been some noticeable damage to the leading edge. Mechanical structures tend to break at the weakest points, which in aircraft impacting horizontally, is for cabin failure forward and aft of the wings, and near door openings. One possible visualisation is for the rear section, around 73/74, to become detached at impact (rotate to the rear), to rapidly submerge, followed by the buoyant VS in turn becoming disentangled and returning to the surface.
With regard to whether or not impact was horizontal or vertical; aside from the relatively intact galleys etc, and the deformation evidence in the recovered wreckage, the pathology tells its own story. In studies on the analysis of the pattern of injuries (Nato study - Cullen et el 1980), it was demonstrated that the pattern of injuries in water impacts strongly correlated with aircraft attitude at the time. In one example, those in the rear of an aircraft incident suffering a tail down impact were likely to be more severely injured than those in the front - the implication here being that a typical passenger carrying aircraft crash is likely to result in either a pattern of uniform injuries or a steady logical gradation in severity (TWA800 being the exception). Given that the 43 recovered bodies were distributed between rows 1 to 42, the forensic pathology would have provided similar clues as to the nature of AF447's attitude at the time of impact - and as the BEA have concluded, was probably horizontal. The fact that 43 appear to have suffered pelvic fractures strongly suggest that they were seated at the time and in their designated positions.
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