Annual Demand

Annual Demand(AD) (年間請求数)

AD is an output variable (Reports/Output by Site) representing the number of demands expected during a year for an item at the location indicated. For an LRU at a site, the formula is as follows:

MRR6 represents the maintenance replacement rate per million hours of one unit of the item on a single end-item or system. PHR represents the peak operating hours per week; 52 is the number of weeks per year; QPEI represents the quantity of the LRU in an end-item or system; and NSS represents the number of systems per site. Note that variables such as DC (duty cycle), NFF (no fault found), and RIP (repair in place) have already been taken into account in the computation of MRR6.

For an SRU or sub-SRU the formula above is applied to the item characteristics (note that QPEI is the number of the SRU or sub-SRU in a system). Then the formula must be multiplied by 1 - the NRTS (not reparable this station)  rate at the site for the parent(s). For example, if an LRU parent has a NRTS rate of .4 for the site, only .6 of AD computed for the SRU occurs at the site.

At a higher echelon site, AD must be multiplied by the NRTS fraction for the item which reaches that echelon, and summed across the number of lower echelon sites whose demand is aggregated for that higher echelon site. For example, if .3 of the demand for an item is repaired at the operating site and there are five operating sites per intermediate site, then the AD for the item at the operating site is multiplied by (.7)(5) = 3.5 to obtain the intermediate site annual demand. If an additional .2 of the demand is repaired at the intermediate site, only .5 of the original demand per operating site reaches the depot in a 3-echelon problem. Thus the depot annual demand would be .5 times the total number of operating sites (there is one depot) times the AD at an operating site.

The principal reason that AD is shown in the output is to provide a check to the user that his data entries for MRR6 (Maintenance Replacement Rate) or MTBF (Mean Time Between Failures), NRTS (Not Reparable This Station), PHR (Peak Operating Program), and NSS (Number of Systems per Site) are correct. AD is even more important as a sanity check for the demand on common items.

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