aircraft Maintenance includes inspection, repair, overhaul, and the replacement of parts. 

Aircraft maintenance is the performance of tasks required to ensure the continuing airworthiness of an aircraft, part, or component. This includes overhaul, inspection, replacement, defect rectification, and the embodiment of modifications, compliance with airworthiness directives and repair.

Maintenance consists of a mixture of preventive and corrective work, including precationary or preventative work (scheduled) ensuring no undetected chance failures (i.e. TBO’s and time limited parts). Included are inspections to monitor the progress of known conditional items. If preventive measures have failed, corrective work (unscheduled) repair or replace post-failures tend to be more costly and time consuming. In short, scheduled or preventive work to anticipate and prevent failures, and unscheduled work to repair and/or replace with on-condition maintenance. Worthwhile maintenance must restore the aircraft or component to its original reliability after maintenance, and the cost of the maintenance action must be less than the failure it is intended to prevent.