*4.1. Reliability of Taxonomies Used*

McHugh (2012) interprets the level of agreemen<sup>t</sup> of Cohen's Kappa [46]. This is shown in Table 3 below.


**Table 3.** Cohen's Kappa Level of Agreement. Adapted from: McHugh (2012).

Table 4 below shows the Kappa value of this research's inter-rater concordance with the AIB SME. Table 5 shows the Kappa value of this research's inter-rater concordance with the NCAA SME.

The values showed a moderate to strong level of coherence between the researcher and SME when the MxFACS taxonomy was used to categorise maintenance-related accidents. This suggests that there is a strong research rigour when compared to the levels as shown by McHugh [46].


**Table 4.** Derived agreemen<sup>t</sup> statistics in all levels for researcher and AIB Subject Matter Expert (SME).

**Table 5.** Derived agreemen<sup>t</sup> statistics in all levels for researcher and AIB SME.


The values also show a moderate to strong level of coherence between the researcher and SME when Hieminga's maintenance incidents taxonomy is used to categorise maintenance-related incidents. This suggests that there is a strong research rigour when compared to the levels as shown by McHugh [46].

### *4.2. MxFACS Level 1—Event Outcome*

A total of 70 accident reports were analysed, however, only 11 of them were identified with maintenance-related causal or contributory factors. These 11 events were then categorised in accordance with the MxFACS taxonomy to highlight the nature of the event. A new coding of "other" was created and added to the taxonomy to categorise maintenance-related events that did not match any of the themes. Table 6 Shows level 1 (Event Outcome) in detail




**Table 6.** *Cont*.

The data highlight that in all maintenance-related Event Outcomes, only terrain collision led to a fatal accident, which was 18% of all maintenance-related accidents in the last decade [47]. This correlates with EASA [7] which identified terrain collision as one of the KRAs, further supported by the global accident/serious incident review in 2018 [36].

Surprisingly, runway excursion and ground collision, which have a high potential to be caused by maintenance error, were not a ffected in the last decade [7]. Only 16 percent of all accidents in the last decade are related to maintenance error. This could be due to inadequate focus given to this safety critical aspect of aviation.
