Lay Up (LU), Periodic Maintenance (PM), Start Up (SU), along with which other PMS periodicity code comprise the four Inactive Equipment Maintenance (IEM)?

The correct choice is Operational Test (OT) because it is specifically designated as one of the four Inactive Equipment Maintenance (IEM) periodicity codes. Inactive Equipment Maintenance refers to maintenance tasks performed on equipment that is not currently in active use but requires regular monitoring and maintenance to ensure it remains in good condition.

Operational Tests are important in this context as they evaluate the readiness and functional integrity of equipment, confirming that it can be reactivated efficiently when required. This testing ensures that all equipment remains reliable and safe, even when it is not in regular operation.

The other periodicity codes like Routine Check, Emergency Maintenance, and Monitoring Inspection do not fit into the defined four categories of Inactive Equipment Maintenance. While they are important maintenance activities, they serve different purposes or types of service that pertain to either active maintenance or specific responses to equipment issues rather than the structured periodicity applied to inactive equipment.