Preventive Maintenance (PM)
Maintenance carried out on a schedule — by calendar or by runtime — to prevent failure rather than respond to it. The alternative, running assets to failure, is the most expensive maintenance strategy there is.
The metric that matters is PM compliance: the share of scheduled work actually completed. Below a certain level the schedule has stopped describing reality, and the useful response is diagnostic rather than disciplinary — either the team is understaffed, or the programme has generated more work than the asset base needs.
And the strategy should follow criticality, not uniformity. The corridor extract fan can reasonably run to failure. The chiller cannot. Spreading maintenance evenly across everything is peanut-butter, and it under-serves exactly the assets that matter.