A formal and structured approach to the use of task analysis in accident modelling

involving the application of formal notations to analyse accident reports has shown that the quality of these accident reports is poor, so much so that their conclusions can be misleading. The proposed solution has been to use formal notations in combination with traditional analysis to produce a report, the conclusions of which can be veriied by formal reasoning. However, there are weaknesses with the formal notations used up until now. Firstly, t h e y h a ve not allowed the representation of all aspects of an accident o r i n c i d e n t. In particular, human factors have either not been represented or not clearly delineated from system factors. In particular, there has not been an attempt to provide a task analysis of the incident. It will be shown how s u c h a task analysis can be provided within a formal model. The advantages of this approach will be explained. Secondly, the notations used do not easily facilitate the system engineering concepts of modularity, encapsulation, or scalability. In consequence it is diicult to model diierent aspects of an accident, compose these diierent aspects to build up the model, or make c hanges to parts of the model without aaecting the rest of the model. This paper explains how the most mature of the formal object-oriented speciication languages, Object-Z, can remedy these problems. An air accident i n vestigation report, issued by the Civil Aviation Authority, is used as a case-study.