Savvy facilities folks recognize the well established hierarchy of maintenance practices with reactive (breakdown) maintenance at the bottom, scheduled preventive maintenance (PM) and reliability-centered maintenance (RCM) as rungs, and predictive maintenance (PdM) as the best practice.
When it comes to instrumentation and controls, most plants are somewhere between reactive and preventive maintenance, spending their resources on doing a combination of emergency repairs and tasks on a fixed schedule, whether or not they're needed. RCM uses asset information and histories to improve the effectiveness of PM, and it helps, but it can't cope with random failures and outliers, so downtime often remains unplanned.