What type of maintenance is completed due to unexpected issues?

Unscheduled maintenance is defined as maintenance that occurs as a result of unexpected issues that arise during the operation of an aircraft or its systems. This type of maintenance is necessary when there are unforeseen problems, such as equipment failures, safety concerns, or system malfunctions that require immediate correction to ensure the continued safety and airworthiness of the aircraft.

Unscheduled maintenance is crucial in aviation, as it directly addresses issues that could potentially lead to dangerous situations if not promptly managed. For example, if a pilot notices abnormal behavior in an aircraft system during pre-flight checks or while in flight, unscheduled maintenance would involve addressing that specific problem to rectify the issue and ensure safe operation.

In contrast, scheduled maintenance involves planned checks and repairs that occur at regular intervals, based on a set timetable determined during the design and maintenance planning of the aircraft. Regular maintenance typically refers to routine inspections and tasks that are performed to maintain the aircraft's condition and performance over time.

Preemptive maintenance refers to performing maintenance before a fault occurs, based on predictive techniques to help avoid failures. This is a proactive approach rather than reactive, which is more in line with unscheduled maintenance.