Page "American Airlines Flight 587" Paragraph 23

According to the official accident report, after the first officer made his initial rudder pedal input, he made a series of alternating full rudder inputs.

This led to increasing sideslip angles.

The resulting hazardous sideslip angle led to extremely high aerodynamic loads that resulted in separation of the vertical stabilizer.

If the first officer had stopped making these inputs at any time before the vertical stabilizer separation, the natural stability of the airplane would have returned the sideslip angle to near 0 °, and the accident would have been avoided.