A maintenance log can be tied to only a single incident. This incident, which is always tied to a single system tree item, must already exist in the System file. For example, assume that a repair technician is sent out to address the failure of the motherboard in a tablet PC. Before the maintenance technician can insert a maintenance log in which to record the replacement of the defective board, the incident reporting its failure must already exist in the FRACAS Incidents table.

To obtain accurate failure rate or repair calculations for a system tree item, the appropriate number of maintenance logs must be inserted. For example, if the repair technician who was sent out to address the failure had to replace two boards, then to obtain accurate failure rate or repair calculations, he must insert two maintenance logs for this incident. However, you only need to enter two separate maintenance logs if you are running MTB calculations.

To calculate MTTR, you must fill in Number of Men and Elapsed Maintenance Time so that a total maintenance time can be computed. For more information, see MTTR (Mean Time To Repair). For MTTR calculations, you can enter repair time in hours or minutes (default). The units are specified by General > Repair Time units in the Project properties. For more information, see General Project Properties.

Because more than one maintenance log may be necessary to address an incident, you can tie multiple maintenance logs to the same incident. Because an incident is tied to only a single item in the system tree, if the maintenance action affects multiple items, separate incidents must be inserted for each affected item.

When System Tree ID Override is inserted in the FRACAS Maintenance Logs table or on one of its forms, you can use it to select a different system tree item for MTTR calculations. By default, when you insert a new record, the value for System Tree ID Override is blank. This indicates that the maintenance log is tied to the item to which the corresponding incident is tied. If you select a different value for System Tree ID Override, this item is then used for calculations.

Selecting an override does not affect the values displayed in any foreign fields from the System Tree Items table that are inserted in the FRACAS Maintenance Logs table or on a Maintenance Logs form. The system tree data shown is always based on the item to which the incident for the maintenance log is tied.