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I don't think the delamination was the primary cause -- it was a result of the design defect, and resulted in the failure of the vertical tail and subsequent loss of the aircraft.

Reading between the lines, I think this is what happened during the flight: the aircraft flew through a wind gust or wind shift that quickly increased the airspeed (relative to the wind) to a level above that allowed for the low speed rudder setting.

For example (and I don't know the exact numbers here), at airspeeds below say 180 KIAS, the allowable rudder deflection might be 30 degrees. Above say 180 KIAS, the allowable rudder deflection might be 15 degrees. At higher airspeeds, say 250 KIAS, the allowable rudder deflection might be 10 degrees. Since rudder force is proportional to the square of the velocity, the maximum allowable deflection at a given airspeed is set so as to provide sufficient yawing moment but not allow excessive yawing moment.

If the airplane was flying at say 175 KIAS and the pilot moved to maximum deflection of 30 degrees, the flight control system would command 30 degrees and the vertical tail and rudder would be below the maximum allowable loads. If a wind shift occurred during or after this rudder deflection, and the airspeed increased to say 250 knots, the rudder, which is still deflected at 30 degrees, would cause a high yawing moment and the load on the vertical tail might be above the allowable maximum load. The pilot might try to compensate by turning the rudder in the opposite direction which might exacerbate the flight upset. This might cause failure of the rudder and departure of the rudder from the aircraft and subsequent aircraft crash.

I postulated this theory at work (an aircraft component manufacturer - I'm an aerodynamics engineer) and on one of the crash boards after the crash. It's good to see it proven out.