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<p>Composite materials used in the aviation industry are known to be more complex than their metallic predecessors. This impacts not only the design and manufacturing of composite structures, but also the failure studies when these structures fail and break (as may be the case in an aircraft accident). Additionally, when under combustion, composite materials introduce potential health hazards. At elevated temperatures, the fibers can be released, presenting an inhalation hazard. Similarly, the matrix decomposition results in a series of potentially toxic byproducts. When encountering composite fires at aircraft accident sites, a series of protocols have been delineated by the corresponding agencies. These include wearing personal protective equipment as well as the application of so-called fixant solutions over the burning composites, with the latter being the focus of this study. The purpose of the fixant solutions is to provide a film of protection that – in essence – holds down small fibers and prevents them from becoming airborne. While the use of fixant solutions is necessary to protect the health of individuals in the vicinity of burnt composites, the potential detrimental impact the application thereof has on fractographic evidence should also be considered. Experts in the field have voiced concerns regarding the use of fixants, outlining that these chemicals may wash evidence away, cover up evidence, or interfere with imaging methods needed during the failure analysis. The purpose of the conducted research, thus, was to compare the relative impact of four commonly used fixant solutions – namely water, wetted water, polyacrylic acid (PAA), as well as a mixture of water and floor wax – on fractographic features of failed carbon fiber/epoxy composite specimens. Specifically, fractographic evidence of two forms of damage – impact and tension – were evaluated. With this goal, the methodology included steps to manufacture the specimens of interest, introduce the two forms of damage, burn the specimens, apply fixants, and perform the microscopic analysis via a scanning electron microscope (SEM). The fractographic evidence prior and after the application of fixant was evaluated qualitatively and quantitatively. The results showed that the evaluated fixants did influence the fracture surfaces imaged, and in certain cased obscured evidence of interest. Additionally, differences between the fixants were ascertained for both forms of damage evaluated. The water treatment was found to perform the best, minimizing the disruption of evidence. Nonetheless, while the study did answer the research questions and the different treatments were compared, additional areas of research and factors that should be considered were identified. </p>

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Approved for public release, distribution is unlimited / 235 Class A Navy and Marine (Naval) aviation mishaps involving aircrew error between FY 90 and FY 98 are analyzed for the possibility of being weather related. In addition to determining the overall role of weather, weather related mishaps are compared to aircraft category, mishap characteristic, the Naval Safety Center human factors (HFACS) taxonomy, and flight phase. In addition, weather related mishap trends have been analyzed. Results show 19% of mishaps involving aircrew error are weather related with helicopter category and controlled flight into terrain (CFIT) mishap characteristic having the largest percent of weather related mishaps for their respective groupings. Visibility related weather elements account for over half of all weather related mishaps, and nearly two-thirds of all weather related mishaps were judged to be preventable with a perfect weather forecast believed by aircrew. These and other findings are presented to develop intervention strategies for reducing the number of weather related flight mishaps (FMs) per year. / Lieutenant Commander, United States Navy