*Article* **A Systematic Methodology for Developing Bowtie in Risk Assessment: Application to Borescope Inspection**

### **Jonas Aust \* and Dirk Pons \***

Department of Mechanical Engineering, University of Canterbury, Christchurch 8041, New Zealand

**\*** Correspondence: jonas.aust@pg.canterbury.ac.nz (J.A.); dirk.pons@canterbury.ac.nz (D.P.); Tel.:+64-33-695-826(D.P.)

Received: 5 June 2020; Accepted: 25 June 2020; Published: 29 June 2020

**Abstract:** Background—Bowtie analysis is a broadly used tool in risk managemen<sup>t</sup> to identify root causes and consequences of hazards and show barriers that can prevent or mitigate the events to happen. Limitations of the method are reliance on judgement and an ad hoc development process. Purpose—Systematic approaches are needed to identify threats and consequences, and to ascertain mitigation and prevention barriers. Results—A new conceptual framework is introduced by combining the Bowtie method with the 6M structure of Ishikawa to categorise the threats, consequences and barriers. The method is developed for visual inspection of gas turbine components, for which an example is provided. Originality—Provision of a more systematic methodology has the potential to result in more comprehensive Bowtie risk assessments, with less chance of serious omissions. The method is expected to find application in the broader industry, and to support operators who are non-risk experts but have application-specific knowledge, when performing Bowtie risk assessment.

**Keywords:** Bowtie analysis; risk assessment; safety; MRO; visual inspection; cause–consequence analysis; barrier model; 6M; Ishikawa; aircraft maintenance
