Here are some clips from the NTSB Safety Recomendation document:

"The Board notes that, at the time the vertical stabilizer and rudder separated from the airplane, the airplane was flying at 255 knots indicated airspeed (KIAS), which is significantly below the airplane’s design maneuvering speed of 273."

"Transport-category airplanes certified by the Federal Aviation Administration (FAA) must meet the airworthiness standards in 14 CFR Part 25. Subpart C, pertaining to the airplane structure, includes Section 25.351, titled “Yaw maneuver conditions,” which requires that the airplane be designed for loads resulting from the following series of maneuvers in unaccelerated
flight, beginning at zero yaw: (1) full rudder input resulting in full rudder deflection (or as limited by the rudder limiter system); (2) holding this full deflection input throughout the resulting over-swing5 and steady-state sideslip angles; and (3) while the airplane is at the steadystate
sideslip angle, a release of this rudder input and the return of the rudder to neutral. The A300 was certified as having met this regulatory standard. In other words, the airplane must be designed to withstand the results of a full rudder input in one direction followed by (after the airplane reaches equilibrium) a release of that rudder input. It is noteworthy that these certification requirements do not consider a return of the rudder to neutral from the over-swing sideslip angle, nor do they consider a full rudder
movement in one direction followed by a movement in the opposite direction. Although, as previously mentioned, most transport-category airplanes are equipped with rudder limiter systems that limit rudder deflection at higher airspeeds, which prevents single rudder inputs from causing structural overload, the Safety Board is concerned that pilots have not been made aware that, a full or nearly full rudder deflection in one direction followed by a full or nearly full rudder deflection in the other direction, even at speeds below the design maneuvering speed, can dramatically increase the risk of structural failure of the vertical stabilizer or the rudder."