## 6 Discussion
### Implications for Practitioners  
This work assessed the performance of different technologies for visual blade inspection. In this context, 3D scanning showed the highest inspection accuracy, while offering the ability to quantify the defect. However, it is not always technically feasible (e.g., in a borescope inspection) nor economically viable. In such instances, software might be a more suitable option. The choice of the type of software is dependent on the number of parts being inspected each year and the ratio of defective blades. If the sample size is sufficiently large for deep learning, then an AI approach could be used, which provides the most flexibility. Previous research [88] showed that similar performance can be achieved using conventional image processing approaches. This is particularly beneficial if only a few samples parts are available. One of the advantages of advanced technologies is the documentation of inspection findings. 3D scanning would enable the creation of a digital twin (model) of the blade. This might enable tracking the deterioration and wear of a part over time and could possibly be fed back into the design process of new engine blades (reverse engineering). The visual-tactile inspection of engine blades is a tedious and highly repetitive task. There is a risk of causing numbness, wrist joint pain or upper limb disorder [101; 102]. Thus, considering 3D-scanning could not only improve the inspection quality, but might be also interesting from an ergonomics and health & safety perspective. To ascertain if advanced technologies can be superior to the human performance by overcoming human factors, more comparisons are required [85]. The most suitable inspection tasks for automation are typically ones with large volumes, high speeds and \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Human Operator**} & \multicolumn{2}{c}{**Advanced Technology**} \\ \hline \multirow{8}{*}{Benefits} & \(\bullet\) & Applies common sense & \(\bullet\) & 24/7 availability \\  & \(\bullet\) & Sophisticated decision- & \(\bullet\) & Faster processing, thus higher \\  & \(\bullet\) & making capabilities & efficiency \\  & \(\bullet\) & Strong cognitive ability & \(\bullet\) & Higher system repeatability \\  & \(\bullet\) & Versatility & \(\bullet\) & Rational and unbiased decision \\  & \(\bullet\) & General intelligence & \(\bullet\) & making \\  & \(\bullet\) & Ability to ask questions and & \(\bullet\) & Excels at dealing with large \\  & \(\bullet\) & overcome uncertainties & \(\bullet\) & amounts and high-dimensional \\  & \(\bullet\) & Improves with experience & & data \\ \hline \hline \multirow{8}{*}{Limitations} & \multirow{8}{*}{Affected by human factors} & \(\bullet\) & Lacks contextual knowledge \\  & & \(\bullet\) & Difficulties with decisions that \\  & & & require general understanding \\ \cline{1-1}  & \(\bullet\) & Affected by human factors & \(\bullet\) & High implementation cost \\ \cline{1-1}  & \(\bullet\) & Prone to err & \(\bullet\) & Often requires other assisting \\ \cline{1-1}  & \(\bullet\) & High inconsistency & \(\bullet\) & Technological dependency \\ \cline{1-1}  & & & \(\bullet\) & May cause laziness and \\ \cline{1-1}  & & & \(\bullet\) & Lack of understanding the effect \\ \cline{1-1}  & & & & the decision has (look-ahead [100]) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Benefits and limitations of humans versus advanced technologies. simultaneous checks. Less suitable are inspections of complex parts with rare defects under varying conditions that require contextual knowledge and complex reasoning. When the assessment of advanced technology does not provide satisfying performance results, an alternative improvement strategy should be chosen. Rather than investing into potentially expensive technologies, a company could, in such circumstances, aim to provide better training [103], optimised workplace design [104], revised standards [105] and improved processes [105].