"Airbus designed and produced the A300B2-1a in 1971. Eleven years later, Airbus designed the rudder control unit in a new model called the A300B4-600. This unique design dramatically changed the handling characteristics of the airplane....
"The pilots operating the accident airplane were highly-skilled, fully-qualified, proficient aviators who were never informed of the unusual limitations of their airplane." 
The relatively intact 27-foot-tall stabilizer was found floating in the Jamaica Bay. It was originally connected to the fuselage at six attaching points, each of which had two sets of attachment lugs, one made from plastic, the other of aluminum. They were held together by a titanium bolt. An examination revealed the metal components to be intact and the plastic lugs to be broken. 
The NTSB did not find any fault with the composite plastic design of the tail fin; however, it did immediately order a one-time visual inspection of all A300-600 and A310 tail fins within 15 days to look for "edge delaminations, cracked paint, surface distortions, other surface damage, and failure of the transverse (side) load fittings. Similarly, indications of failure of the rudder assembly, which could lead to failure of the vertical stabilizer, may be detectable with such an inspection." 
Ellen Connors, the former chairperson of the NTSB has stated that the report was delayed because of "inappropriate and intense lobbying by Airbus over its contents" and that "the potential for contaminating the investigation exists." 
Following the crash of AA587, United Airlines decided to go beyond the required visual inspection to conduct ultrasound tests on three of its A320 jets, whose plastic tail fins had also been repaired at the factory before delivery. The test found a flaw in a six-year-old A320 on the opposite side of the stabilizer from where the factory defect had been repaired. In spite of the defect, Airbus spokesman David Venz said the defect is in an area that doesn’t support the weight of the tail. He said, "We are confident this airplane is fit to fly." 
Airbus claimed that damage that couldn’t be seen cannot weaken the plastic tail fins and that visual examinations were sufficient. One official said, "Invisible damage cannot produce a significant sub-surface flaw." 
Unconvinced, some American Airlines pilots called for more detailed inspections, such as ultrasound to locate hidden flaws. 
More than 20 American Airlines pilots asked to be transferred to Boeing aircraft, "although this meant months of retraining and loss of earnings." One pilot wrote that "he had refused to let any of his family take an A300 or A310 and had paid extra to take a circuitous route on holiday purely to avoid them." 
Saying there was no way to adequately inspect the plastic tail fins, dozens of American Airlines pilots demanded that the company ground its fleet of Airbus A300 jets until the cause of the crash of AA587 could be determined.
More than 70 pilots signed a statement stating, "Until a definitive cause for the crash of Flight 587 can be determined, along with ways to prevent a similar occurrence, and/or a definitive test can be developed to truly check the structural integrity of the vertical stabilizers of our remaining 34 A300s, I recommend that American Airlines’s fleet of A300s be grounded." 
Weighing in on the side of the pilots, Professor James H. Williams, Jr., of the Massachusetts Institute of Technology, School of Engineering, stated that the Airbus position regarding the adequacy of visual inspections was "lamentably naive policy. It is analogous to assessing whether a woman has breast cancer by simply looking at her family portrait." 
Regarding the repairs performed by Airbus on composite tails with discovered defects prior to deliver, Dr. Williams states, "Such repairs of structural damage in composites are frequently unreliable, especially for joints and attachments involving primary (load-bearing) structures. The rupture of the vertical stabilizer on Flight 587 occurred in the vicinity of repairs, adjacent to an attachment point. Therefore, the FAA must carefully establish and articulate a policy for the repair of primary composite structures." 
"Finally," Dr. Williams concludes, "Airbus’s extensive design and testing programs for the A300-600 composite vertical stabilizer may be currently deficient if they were based on outmoded or flawed engineering assumptions or an inadequate certification process. No amount of analysis can overcome faulty assumptions or insufficient requirements." 
Even in the absence of an overloading or catastrophic event, Dr. Williams believes that, "When subjected to the loading histories of some aircraft, composites will lose both strength and stiffness. Furthermore, studies of the long-term effects of exposure to aircraft environments of moisture, pressure and temperature, as well as fuels, hydraulic fluids, lubricants and deicers remain to be conducted for many composite materials." 
His research has shown that, "repeated journeys to and from the sub-zero temperatures found at cruising altitude causes a build-up of condensation inside composites, and separation of the carbon fibre layers as this moisture freezes and thaws." Dr. Williams says it is "like a pothole in a roadway in winter, over time these gaps may grow."