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New York, NY (April 7, 2002) NASA, USAF, former NTSB official warn that visual inspection of composites on aircraft is ineffective. Reports and statements support A300 pilot group's view that visual inspections to find significant damage in composites used on aircraft is ineffective. Pilots urge agencies to immediately use high-tech (ultrasound, etc) inspection techniques, similar to the one that found damage on A300 tail, to ensure safety of A300 fleet.
A study conducted by NASA researchers warned of the use of composite materials in aircraft load-bearing structures and highlighted the need for sophisticated testing equipment to ensure structural integrity of the materials that were in use.
Aviation industry magazine Aviation Today, in an article written by Lee Gaillard, tells of a presentation to the March 2001 convention of the Society for the Advancement of Material and Process Engineering, where C.E. Harris and M.J. Shuart of NASA's Langley Research Center cited a lingering lack of maturity in some areas of "composite structural design and manufacturing technology."
Regarding the manufacturing process, they commented that "curing kinetics are particularly challenging to scale" when one moves from smaller to larger component fabrication. (The time/temperature/pressure variables are crucial.) Furthermore, composite components and structures fail very differently from traditional metal structures. Indeed, "initiation and growth of materials level damage and the failure modes of composite structures are not well understood and cannot be predicted analytically." Compared with most metal components, failure tends to be sudden rather than gradual. In the face of such challenges, airline (maintenance) supervisors face a situation in which "long-term field experience necessary to develop a support infrastructure does not exist for composite structures."
The article also contained a statement by the US Air Force Research Laboratory's Materials and Manufacturing Directorate that supports the pilot's urgent insistence that visual inspections currently being used to detect dangerous damage in composite materials is ineffective.
"Substandard fabrication procedures, environmental exposure and handling, or service damage can all have a negative impact on the mechanical integrity of these structures without affecting their visual appearance," the Directorate said in a statement on the subject.
The eight-member task force of commercial airline pilots filed a comprehensive research study in late March with the NTSB and the FAA that raises questions about aircraft construction and certification practices, as well as other issues surrounding the crash of an airliner in New York last November.
The pilots call upon the FAA and the NTSB to address several areas of concern. They hope to influence the agencies and airline managers to take a hard look at what they say has been an inadequate response to information discovered from the AA Flight 587 crash.
In a 72-page document, the pilots outlined worries about inspections, certification standards, the durability and proper use of composite materials and specific concerns with the Airbus A-300-600. They also urged the agencies to immediately conduct high-tech, ultrasound inspections on all parts of all A300 tails sections before the planes are then released to fly.
The pilot's views are shared by an increasing number of aviation industry experts and composite engineers. Dr. Bernard Loeb, former director of the NTSB's Office of Aviation Safety, told the Dallas Morning News that, while he agrees with the FAA's decision not to ground the A300-600 fleet at this time, he would favor relatively rapid, ultrasonic inspections of all the planes. He noted that an earlier visual inspection had not revealed damage to the plane involved in the 1997 incident.
"The notion that a visual inspection is adequate is a bankrupt notion."
Dr. James Williams, Professor of Applied Mechanics in the Mechanical Engineering Department at the Massachusetts Institute of Technology, told NBC news that:
"Visual inspection is simply the lowest level at which one would want to inspect one of these structures. Invariably, one would want to do more in order to increase a sense of reliability or comfort with respect to their integrity." Airbus Industries takes the position that if delamination can't be seen on the outside, there is no problem. According to a recent Airbus statement: "Because non-visible damage does not reduce strength below requirements and will not grow."
"That is basically a ludicrous statement," said Williams.
"We discovered that many experts have serious disagreement with the Airbus engineers and others that advocate only visual inspections for composites used in critical aircraft parts like the tail section that broke off AA 587. We feel that, with all of the "unknowns" in this investigation, a more conservative path would be more appropriate," said Jason Goldberg, an A300 pilot.
Copies of the report can be obtained by download at http://www.usread.com/airbusa300pilots/, calling either of the telephone numbers above or by e-mail request at: firstname.lastname@example.org.