Reasoning about Human Error and System Failure for Accident Analysis

Abstract

Accident reports are produced by regulatory and commercial authorities, such as the UK Air Accident Investigation Branch and the US National Transportation Safety Board, in response to most major accidents. These documents describe the human and system failures that lead to major accidents. Recommendations are then made so that the operators and regulators of safety-critical systems can avoid future accidents. Unfortunately, it is often difficult for readers to trace the way in which particular conclusions are drawn from the many hundreds of pages of evidence in these reports. Natural language arguments often contain implicit assumptions and ambiguous remarks that prevent readers from understanding the reasons why a particular conclusion was drawn from a particular account. Operator error is frequently blaimed for accidents that might equally have been blaimed upon poor systems engineering or interface design. This paper, therefore, argues that mathematical proof techniques can be used to support the findings of accident investigations. These techniques enable analysts to formally demonstrate that a particular conclusion is justified given the evidence in a report. The later sections of this paper then introduce Conclusion, Analysis and Evidence diagrams. These can be used to communicate the results of a formal analysis. The intention is not to replace the natural argumentation structures that are currently used in accident reports. Rather, our aim is to increase confidence that particular conclusions are well supported by the evidence that is presented within a report.Keywordsaccident analysisformal methodshuman factorsdesign rationale, CAE diagrams.