The system's deterioration goes through a three‐stage process, namely, normal, minor defective and severe defective.
Two levels of inspections are proposed, e.g., minor and major inspections.
Once the minor defective stage is found, instead of taking a maintenance action, a shortened inspection interval is recommended.
When the severe defective stage is found, we delay the maintenance according to the threshold to the next PM.
The decision variables are the inspection intervals and the threshold to PM.
