Abstract

When a major engineering product failed, a failure investigation is often conducted to prevent similar failures in the future. In this dissertation, I propose an account of the epistemology and methodology of engineering failure investigations, based on a close examination of the documentations on five major plane crash investigations conducted by the National Transportation Safety Board (NTSB). The dissertation is divided into three parts. The first part consists of the five case studies arranged in chronological order: the American Airlines Flight 191 accident in 1979; the United Flight 232 accident in 1989; the United Flight 585 accident in 1991; the USAir Flight 427 accident in 1994; and the TWA Flight 800 accident in 1996. In each case study, I summarize the entire investigation process, focusing on articulating the questions that arise and the evidential reasoning that helped resolve each question. The second part of the dissertation examines how the investigators infer causes of failure events. The type of causal inference used in failure investigations typically proceeds from effects to causes, hence it is called reverse causal inference. This is in contrast with forward causal inference, where researchers start with an intervention and infer the effects of that intervention. I identify three types of reverse causal inference in engineering failure investigations: feature dependence, additional outcomes, and process tracing. The third part of the dissertation examines how the investigators construct narratives of failure events. At the end of each failure investigation, the investigators come up with a narrative detailing the sequence of events leading to the outcome. This part of the dissertation examines how the investigators construct such narratives and support them with evidence. I argue that both the construction and the justification of a narrative of a failure event depend on the question-and-answer process in the investigation, which I call the question dynamics of the investigation. I examine three main components of the question dynamics: the resolution of questions, the significance of questions, and the arising of questions. I conclude the dissertation with an account of the coherence of narratives, which is a measure of the evidential status of narratives. My account of coherence relies on the question dynamics, and it captures the intuitive idea that the pieces of a coherent narrative “fit together” very well.