*4.2. Study Conclusions*

The study provides a modern-day and maintenance-specific viewpoint on CAT accidents and serious incidents. The development of theMxFACS taxonomy brings about a contemporary approach for exploring the nature of these maintenance events, by looking at a combination of maintenance-specific causations, system/componen<sup>t</sup> failures, and event outcomes. Such taxonomy output is demonstrated as being applicable to existing risk analysis processes and methods and could be used to complement existing taxonomy and methodologies.

The results of the study show that the three most frequent maintenance events for 2003–2017 are runway excursions, air turnbacks, and on-ground landing gear-related events. The most common system/componen<sup>t</sup> failures were related to engine, landing gear, and flight controls. At the causation level, the largest maintenance factor issues were inadequate maintenance procedures, inspections not identifying defects, incorrect installation, and incorrect procedures.

By combining the frequency of event data with number of fatalities, it was possible to begin to create a picture of the higher risk areas within maintenance for this time period. Collision events were the most prominent consequence, engine-related events were the largest event type, and inadequate maintenance procedures were the most concerning maintenance factor.

The study's findings could be used to aid in a Safety-II approach to understanding where barrier weaknesses lie within maintenance safety managemen<sup>t</sup> systems, particularly when integrated with bowtie analysis. Such an approach may allow regulators and maintenance organisations to develop means of ensuring as much as possible goes right within the maintenance system, as opposed to looking solely at just what went wrong.
