One large national postal operation was using "downtime" as a performance measure for the maintenance departments in its various letter sorting plants. If any "downtime" incident on a piece of letter sorting equipment exceeded 30 minutes, then the incident had to be reported to the head office. National performance, including downtime, were reported across the corporation's plants on a monthly basis. Having the least downtime rapidly became a measure of plant maintenance manager expertise and success - it became a key to "bragging rights". There were no formal implications associated with the measure. To keep downtime to a minimum the maintenance managers, to a man, choose to focus directly on its minimization by speeding up repair times (i.e.: maintainability). None concentrated on minimizing the number of repairs (a reliability issue). To minimize downtime they made sure the spare parts needed for any repairs were stored close to the machines for ready access. This practise is actually one that we'd call successful except for one glitch. Those parts were stored there "off the books". The inventory systems did not track them. They were sometimes restocked when used from stores kept in a storeroom on site and managed by their inventory management group. Because the maintenance technicians were not really thinking about stores and inventory management (after all it's not their responsibility) those local part stores were often short of needed parts. When they were needed in a rush which often took place after the mail arrived at the plant in the evenings when stores were closed, they would hurriedly take parts from stores and fail to record the stock issues. Doing so would have taken time and put their downtime measure at risk. Inventory records for the stores were therefore inaccurate and continually getting worse. Eventually stock-outs occurred and downtime shot up at all the plants.
Inventory values were understated because the stores kept beside the machines were already "issued" by stores and therefore consumed, even though they weren't. Issues after hours were not recorded so inventory accuracy was compromised. As the stock of parts in stores ran down without being replenished by the inventory management system (which actually worked well if it was used correctly) repairs were delayed, parts were being rushed in at high cost and downtime was soaring.
A review of what was happening revealed that the use of a single performance measure, downtime, without any other measures of performance was driving this dysfunctional and costly behaviour. In addition to some inventory management practise changes the performance measures were "overhauled" to ensure one facet of performance (e.g.: maintenance) wasn't improved at the expense of others (e.g.: inventory).
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