According to the official accident report, the first officer repeatedly moved the rudder from fully left to fully right. This caused increasing sideslip angles. The resulting hazardous sideslip angle led to extremely high aerodynamic loads that separated the vertical stabilizer. If the first officer had stopped moving the rudder at any time before the vertical stabilizer failed, the aircraft would have leveled out on its own, and the accident would have been avoided. The aircraft performance study indicated that when the vertical stabilizer finally detached, the aerodynamic loads caused by the first officer's actions produced 203,000 lb of force on the rudder, meaning that the vertical stabilizer did not fail until far in excess of the 100,000 lb of force defined by the design envelope. The vertical stabilizer's structural performance was determined to be consistent with design specifications and exceeded certification requirements.