Which maintenance level is largely concerned with reworking major systems?

The maintenance level concerned with reworking major systems is the D-level, or Depot level maintenance. This level of maintenance involves comprehensive repairs and overhauls, which may include complete restoration or reconstruction of major components and systems within an aircraft. D-level facilities are equipped with specialized tools and skilled personnel who can perform complex tasks that are beyond the capacity of other maintenance levels.

In contrast, O-level maintenance focuses on day-to-day operational checks and minor repairs, typically performed by the flight line personnel. I-level maintenance is responsible for intermediate tasks, including limited repairs, adjustments, and replacements, but does not engage in the extensive reworking of major systems. Understanding the roles of these maintenance levels is crucial for the efficient operation and long-term sustainment of aviation assets.