Which type of maintenance is characterized by discrepancies and deficiencies found during operations?

Unscheduled maintenance is characterized by work that is carried out in response to discrepancies and deficiencies that are identified during operations. This type of maintenance is often unplanned and can arise from unexpected events, equipment failures, or findings during routine inspections.

In aviation, unscheduled maintenance is critical because it ensures that any issues that could affect safety or operational efficiency are addressed promptly, maintaining the integrity of the aircraft. Aircraft are regularly subjected to checks and inspections that may reveal problems; when these occur outside the normal schedule, maintenance teams must react quickly to resolve them, minimizing downtime and ensuring safety.

Scheduled maintenance, on the other hand, refers to routine checks and services performed at predetermined intervals to ensure aircraft readiness. Rework and upkeep generally involve repetitive tasks that do not stem from immediate operational findings. A phase inspection is a thorough, systematic review of specific systems and components, typically outlined in the maintenance program, but it does not directly relate to unscheduled circumstances.