NASA/SP-2011-3423, NASA SPECIAL PUBLICATION: NASA ACCIDENT PRECURSOR ANALYSIS HANDBOOK (DEC-2011)

NASA/SP-2011-3423, NASA SPECIAL PUBLICATION: NASA ACCIDENT PRECURSOR ANALYSIS HANDBOOK (DEC-2011)., The Accident Precursor Analysis (APA) process described in this handbook provides a systematic means of analyzing candidate accident precursors by evaluating anomaly occurrences for their system safety implications and, through both analytical and deliberative methods used to project to other circumstances, identifying those that portend more serious consequences to come if effective corrective action is not taken. APA builds upon existing safety analysis processes currently in practice within NASA, leveraging their results to provide an improved understanding of overall system risk. As such, APA represents an important dimension of safety evaluation; as operational experience is acquired, precursor information is generated such that it can be fed back into system safety analyses to risk-inform safety improvements. Importantly, APA utilizes anomaly data to predict risk whereas standard reliability and PRA approaches utilize failure data which often is limited and rare. The purpose of the APA process is to identify and characterize potential sources of safety risk for which indications are received in the form of anomalous events which, although not necessarily presenting an immediate safety impact, may indicate that an unknown or insufficiently understood potential risk-significant condition exists in the system. Such anomalous events are considered to be potential accident precursors because they signal the potential for more severe consequences that may occur in the future, due to failure mechanisms that are discernible from their occurrence today. Their early identification allows them to be fully scrutinized and the results to be used to inform decisions relating to safety. Stemming from the anomalous event that was actually observed, the NASA process invokes an “imaginative” aspect to the process using a structured brainstorming session to identify similar anomalous conditions which could have more severe consequences than the observed anomalous event. In the context of NASA systems, the term severe consequences typically refers to loss of crew (LOC), loss of vehicle (LOV), loss of mission (LOM), or loss of science (LOS). It is up to the particular program employing the approach to define severe consequences appropriate to its objectives and apply the technical approach accordingly. The APA process presented in this document has been applied to earth-to-orbit transportation systems and crewed orbital science platforms, although the fundamental process steps are valid for other mission classes (e.g., crewed and uncrewed orbital platforms, crewed lunar and planetary outposts, deep-space robotic missions, and other human space exploration missions), and may be tailored to the specific needs of each class. Programs at NASA that have benefited from the APA process presented in this document include the Space Shuttle and the ISS. In addition, NASA is continuing to exercise a robust terrestrial and solar system satellite and robotic based science agenda that could benefit from a systematic APA process. In this case, an accident precursor process could provide valuable information to guide the design of future scientific missions as well as indicate when corrective actions are required during the mission to preclude potential mission-ending failures. Finally, APA plays an important role in extending NASA\'s anomaly management process to provide additional screening and assessment of anomalies for their risk significance.