Using a Formal Language to Support Natural Language in Accident Reports

Accident reports written by oocial bodies, such as the Air Accident Investigation Branch of the United Kingdom's Department of Transport, are produced in response to all major civil aircraft accidents or incidents. There are many statutory, legal and commercial implications that rest on the analysis, conclusions and recommendations that these reports contain. Air accident reports usually follow a standard format of synopsis followed by factual information, including history of ight and the systems involved, followed by analysis and conclusions. Finally, there are safety recommendations aimed at preventing a recurrence of the accident. Natural language is the primary means of communicating all of these nd-ings. In requirements engineering there is an increasing recognition that natural language is not always an adequate means of expressing some of the detailed reasoning associated with the causal analysis of complex systems. Recent work in software engineering has explored the use of formal, mathematically based, techniques to help gain the required level of clarity and precision. We argue that accident reports, like requirements documents could beneet by the use of formal techniques to complement the usual natural language descriptions. In this paper we consider one speciic accident report. The limitations of its natural language descriptions are examined and we explore the use of a Petri Net notation to help elucidate its ambiguities.