*3.5. Level 3—Maintenance Factors*

Coding at the third level of the MxFACS taxonomy revealed 221 maintenance factors which were identified as contributory to the events in the dataset. The high-level maintenance factors are shown in Figure 7.

As with previous studies [2,3,22] cited in [23–25] omission errors, particularly incorrect installations, remain prevalent. However, the number of commission errors (procedures undertaken but not to an appropriate level) are also of note. Particularly inadequate maintenance procedures, which are not only the largest commission error but also the leading maintenance factor overall. Inspections, incorrect procedures, and operator oversight are further areas of significance within the dataset.

An initially surprising result is the low presence of human factors (HF) analysis within the published accident/serious incident o fficial reports. The data was coded based only on the information available; the researcher did not make any assumptions about the HF nature of maintenance factors. Whilst many of the reports detailed HF information for how the flight crew responded to the situation created as a result of the maintenance factors, little or—in many cases—no attention was given to the human performance issues from the maintenance perspective. This raises the question as to why in-depth HF analysis related to maintenance personnel is not conducted during the investigations. This is one of the most significant findings of this study. Just like the flight crew, maintenance personnel performance relies on a wide range of factors from a personal and organisational perspective, to an industry-wide sociotechnical system level.

There is no doubt the investigators are constrained by many factors and finding out facts about the issues impacting on performance of the individuals involved during an investigation can be very challenging and—in some cases—impossible but as Burban [26] suggests there is a reluctance amongs<sup>t</sup> some investigation bodies to fully embrace HF and address potentially important HF issues in detail in their investigations.

Many of the more-detailed maintenance factors have interdependencies where the combination of two or more of these factors led to the event. Identifying these interdependencies allows for an understanding of the barrier failings which lead to an event. One example of this is the 30 July 2008 event where incorrect maintenance procedures lead to a Boeing 777 fuel supply hose O-ring being damaged, thus causing an engine fire from the associated fuel leak. Following the aircraft maintenance

manual (AMM) procedure should normally have prevented this from taking place, however the AMM did not contain the appropriate information for this procedure and thus contributed to the event [27].

**Figure 7.** Level 3 top level maintenance factors.
