**4. Conclusions**

This study provided the risk assessment and optimization of the inspection interval of a composite aircraft tail wing structure. Composite structures are more prone to fatigue delamination damage and such damages can ultimately lead to the catastrophic failure of the complete aircraft composite structures, such as aircraft tail wings. Therefore, different aircraft maintenance strategies were proposed for the accurate prediction of the fatigue life of composite structures. However, the main limitation of the approaches available in the literature is the availability of real aircraft maintenance data to develop structural health monitoring approaches for the prediction of the fatigue life of the composite structures. The acquisition of the real damage data requires the embedding of additional sensors on the skin of aircraft structures, thus making the maintenance strategies more expensive. Therefore, to overcome the unavailability of real-life operating data, the study proposed the methodology of using the FEA-based model for the generation of fatigue damage growth curves and further implemented this approach for the risk assessment and optimization of the inspection interval of the KT-100 aircraft tail wing structure. The overall methodology of the proposed study and the concluding remarks are summarized as follows:


**Author Contributions:** Conceptualization, H.S.K. (Heung Soo Kim) and J.-H.C.; methodology, S.K. and H.-S.K. (Hee-Seong Kim); software, S.K. and H.-S.K. (Hee-Seong Kim); formal analysis, S.K.; resources, H.S.K. (Heung Soo Kim) and J.-H.C.; writing—original draft preparation, S.K.; writing—review and editing, S.K., H.S.K. (Heung Soo Kim), J.-H.C. and H.-S.K. (Hee-Seong Kim); supervision, H.S.K. (Heung Soo Kim) and J.-H.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported under the project "Research and Development of Composite Internal Defect Risk Assessment Method" by the Aero Technology Research Institute and supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (no. 2020R1A2C1006613) and BK−21 four.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.
