**6. Conclusions**

The purpose of this research was to overcome the arbitrariness of the Bowtie methodology. This work makes several novel contributions by addressing the research purpose. Firstly, it provides a structured way of performing Bowtie analysis and constructing the diagram accordingly by following the 6M approach. This required contextualisation of the 6M categories for application in a maintenance area, which di ffers to a production environment. Secondly, it was applied to borescope inspection of aero engine parts and extended the risk analysis beyond the tool (borescope device), and included other relevant risks related to methods, management, material, work environment and human factors.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2226-4310/7/7/86/s1, Figure S1: Full Bowtie diagram with 6M prevention and mitigation barriers; Figure S2: Management-related threat paths with barriers; Figure S3: Material-related threat paths with barriers; Figure S4: Method-related threat paths with barriers; Figure S5: Man-related threat paths with barriers; Figure S6: Mother Nature-related threat paths with barriers; Figure S7: Machine-related threat paths with barriers; Figure S8: Consequence path with a 6M barrier structure.

**Author Contributions:** Conceptualization, J.A. and D.P.; methodology, J.A. and D.P.; software, J.A.; formal analysis, J.A. and D.P.; investigation, J.A.; resources, D.P.; data curation, J.A.; writing—original draft preparation, J.A.; writing—review and editing, J.A. and D.P.; visualisation, J.A.; supervision, D.P.; project administration, D.P.; funding acquisition, J.A. and D.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research project was funded by the Christchurch Engine Centre (CHCEC), a maintenance, repair and overhaul (MRO) facility based in Christchurch and a joint venture between the Pratt and Whitney (PW) division of United Technologies Corporation (UTC) and Air New Zealand (ANZ).

**Acknowledgments:** We sincerely thank sta ff at the Christchurch Engine Centre for their support and providing insights into visual inspection and risk management. In particular, we thank Tim Coslett, Marcus Wade, Tim Fowler and Allan Moulai.

**Conflicts of Interest:** J.A. was funded by a PhD scholarship through this research project. The authors declare no other conflicts of interest.
