Aviation Investigation Report A98H0003

4.2.2  Interpretation of Material Flammability Test Requirements

As a result of the investigation, the TSB previously issued three recommendations on the subject of Material Flammability Standards. Reaction to the content of these recommendations has been positive. Regulatory authorities have largely embraced the need for regulatory changes that would result in no materials being certified that would sustain or propagate a fire, as recommended in A01-02. The FAA is leading a research and development effort as part of the International Aircraft Materials Fire Test Working Group that is developing new flammability tests for materials, including wires and cables, found in "hidden areas." The Board believes that imposing more realistic and thus more severe flammability test requirements will serve to decrease the likelihood of flammable materials being approved for use in the manufacture or repair of aircraft. However, variations still remain in the interpretation and application of the regulations and guidance material.

Throughout this investigation, in an effort to determine the ignition and propagation scenario for the in-flight fire, various materials used in the manufacture of the MD-11 were tested in accordance with the applicable regulatory requirements. In some cases, materials such as silicone elastomeric end caps and hook-and-loop fasteners, demonstrated inappropriate flammability characteristics. Neither the aircraft manufacturer nor the regulatory authority were able to effectively explain whether these or other such materials had been required to be tested and, if so, could not produce a record of the resultant certification test data. It appears that varying interpretations of the same regulations may explain why some materials that were certified for use in aircraft met the flammability standards while others did not. As explained in the TSB's Material Flammability Standards recommendation package (issued August 2001), except for the most obvious and common materials, it was difficult to determine with certainty which flammability test(s) applied to which material. The applicable FARs could be misinterpreted so as to minimize the amount and level of testing required for certification of any particular material.

The certification of a newly manufactured aircraft is a complex endeavour, which includes the certification of many types of materials. The Board expected that as a result of its previous recommendations, regulatory authorities would not only develop improved testing but also simplify the interpretation of the regulations and guidance material so as to prevent the approval of flammable materials. Without such a concerted and focused effort, manufacturers and those responsible for the certification of aircraft materials will continue to operate in an environment where it is possible to misinterpret the regulatory requirements. In such circumstances, materials that exhibit inappropriate flammability characteristics can continue to be approved for use in aircraft. Therefore, the Board recommends that

Regulatory authorities take action to ensure the accurate and consistent interpretation of the regulations governing material flammability requirements for aircraft materials so as to prevent the use of any material with inappropriate flammability characteristics.

Assessment/Reassessment Rating: Fully Satisfactory

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