One approach that has been applied in the never-ending quest for increased aviation safety is designing to accommodate at least a single failure without having a catastrophic event. This is commonly referred to as the failsafe approach. Designing a system to be fail-safe is relatively unambiguous and it has been done over the years with considerable success. However, achieving structural fail-safety can be very much a function of how it is defined, and its success in preventing catastrophic events has been mixed. This paper examines the way structural fail-safety was defined, interpreted and applied subsequent to its introduction into the civil airplane certification requirements in 1956. This paper also summarizes a review that was conducted of some notable incidents with fail-safe structures and identifies what the authors feel are demonstrated problems with the fail-safe approach. Irrespective of known shortfalls, it is concluded that an inherent capability to tolerate the presence of damage can be beneficial, especially relative to unanticipated damaging events. It is therefore suggested that a requirement to design for a minimum level of structural damage capability would be of value. In closing, a structural damage capability requirement that has been proposed by the General Structures Harmonization Working Group of the Aviation Rulemaking Advisory Committee is reviewed.
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