The aim of predictive maintenance is first to predict when equipment failure might occur, and secondly, to prevent the occurrence of the failure by performing maintenance. Monitoring for future failure allows maintenance to be planned before the failure occurs. Ideally, predictive maintenance allows the maintenance frequency to be as low as possible.
Condition-based maintenance refers to maintenance when need arises. Real time data is used to prioritize and optimize maintenance resources. This maintenance is performed after one or more indicators show that equipment is going to fail or that equipment performance is deteriorating.
AOG - Aircraft on Ground
Aircraft on Ground or AOG is a term in aviation maintenance indicating that a problem is serious enough to prevent an aircraft from flying. Generally, there is a rush to acquire the parts to put the aircraft back into service and prevent further delays or cancellations of the planned itinerary.