Parts Fill Rate
The share of parts requests filled immediately from stock, rather than ordered. The link between inventory policy and how long a vehicle sits.
Fill rate measures how often the part is on the shelf when a technician asks for it. Every miss becomes an order, a wait and a vehicle occupying a bay or a yard until the part arrives.
It is the cleanest way to show that inventory is not merely a cost. Parts on a shelf look like money sitting still, and they are an easy target in a budget review, so a fleet that cannot connect stock levels to downtime tends to lose that argument and then absorb the consequence as longer repairs. Fill rate is the number that connects them.
A high rate is not automatically good either, since it can be bought by stocking far too much. The useful version is measured against the parts that actually move, which is why obsolete stock is worth identifying before an inventory conversation rather than during one.
Public fleets have a particular version of the problem: a wide mix of makes, ages and vocational bodies means many more part numbers per vehicle than a standardized commercial fleet carries, which is one of the practical costs of buying the lowest responsive bid over many cycles.
