functional criticality

The functional criticality describes how important the mechanical dependency between two assets (system, assembly or component) is.

For example: An HVAC system is comprised of an air handler unit (AHU), chiller, boiler, duct work, vav, and diffusers. The AHU assembly has a fan assembly which is comprised of the fan, the fan motor, a fan belt, and a filter. The fan motor is functionally critical to the AHU, as the AHU cannot function without it. The diffusers are not functionally critical to the HVAC system or the AHU assembly, as the AHU assembly can function without the diffuser.