The damage tolerance and the widespread fatigue damage philosophies are aimed on protecting the structure from different threats. Whereas the damage tolerance 'rouge flaw' protects the structure from severe rare manufacture anomalies, the widespread fatigue damage assessment protects the aircraft from 'normal' fatigue. In this study we present a case study of the Southwest Airlines accident (flight 812) in 2011, in which a Boeing 737-300 airplane experienced a rapid decompression during flight. A section of the fuselage skin, about 60 inches wide, had fractured and flapped open. An NTSB investigation concluded that one of the skin panels was replaced during assembly, and was installed misaligned, so most of the lower rivet row holes were misdrilled. This accident represents a special and rare case in which the manufacture flaws are spanned within a large region of the airplane. Thus, both damage tolerance and widespread fatigue damage philosophies are not sufficient to ensure the aircraft structural integrity. Risk analysis based WFD assessment presented in this study concluded that an acceptable safety level is reached only if the inspection program is significantly reduced as compared to that defined by the OEM. Discussion on further actions and conservatism is also provided.
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