## 6 Discussion
### Summary of Work
#### 6.1.1 Inspection Performance  
A summary of the achieved inspection performance, measured in inspection accuracy, inspection time and inspection consistency of each inspection agent is presented in Table 6 and further discussed below. Each technological system was limited to the type of inspection it was developed for, while the human operator was able to accomplish all the different inspections. The human operator was more tolerant of different inspection conditions such as dirty blades, different types of defects and different inspection environments (in situ vs. on bench) along with their viewing and lighting restrictions, e.g., in the borescope inspection. This is consistent with [86] who found that the human's cognitive abilities of irregularity recogni \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Piece-Part Inspection**} & \multicolumn{2}{c}{**Borescope Inspection**} & \multicolumn{2}{c}{**Visual–Tactile Inspection**} \\  & **(Image-Based)** & \multicolumn{2}{c}{**(Image-Based)**} & \multicolumn{2}{c}{**(Part-Based)**} \\  & **Human** & **IP Software** & **Human** & **AI Software** & **Human** & **3D Scanner** \\ \hline Inspection Accuracy & 76.2\% & 48.8\% & 63.8\% & 47.4\% & 84.0\% & 100.0\% \\ Inspection Time & 14.972 s & 0.203 s & 20.671 s & 0.025 s & 22.140 s & 55.000 s \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of inspection performance by inspection method and inspection agent. Figure 10: Weighted factor analysis for different inspection agents. tion, decision-making and adaptability to new inspection environments was superior to advanced technologies. There was only one study in the field of visual inspection that allowed for a direct comparison to the present work, which was [PERSON] and [PERSON] [47]. Those authors found that human operators outperformed the automated inspection system. This aligns with our findings, which compared a human to inspection software (image processing or AI based). In the visual-tactile inspection however, the opposite was the case. The 3D scanner did not miss a single defect, whereas the human operator was, on average, only 84% accurate with their inspection. [PERSON] and [PERSON] further stated that humans showed a lower false-positive rate than the automated system [47]. This finding was not supported by the present study, as the software seemed to be less sensitive to anomalies and accepted more non-defective blades than the human operator. While a low false-positive rate is generally desirable, this should not be at the expense of missing critical defects (false-negatives). Another interesting finding of the previous study [47] was that only 56.8% of inspectors detected low-contrast defects such as nicks and dents. Of those, another 24.8% of operators incorrectly classified the defect as acceptable, making it a total of 42.7% of the research population who missed or incorrectly accepted those two defect types. This was somewhat similar to the 38% reported in [10]. The present study confirmed this difficulty that human operators demonstrate when inspecting low-contrast defects in all three inspection types. Particularly in a challenging environment such as in borescope inspections, the detection rate for nicks and dents was poor [10]. Nonetheless, the detection rate was 83% and 87% for nicks and dents, respectively, which is still higher than in [47]. This might be explained by the negative impact a missed defect has in this industry. Those were the same types of defects the IP and AI software struggled with. Thus, there was a similar performance curve for the software across the different types of defects, but overall, it was lower than the human operator. As previously mentioned, this was different for the 3D scanner that detected all defects. Furthermore, [47] concluded that the inspection device had a worse false-alarm rate than the operator. Based on our findings, we would tentatively suggest that a higher false-positive rate would have been acceptable if the majority of defects had been found.