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Cost to Repair Statistics

 
The Cost to Repair metrics, which appear in the Isolation Cost and Time Statistics section of the Fault Isolation Report, describe the cost associated with diagnosing and replacing all items (using Block Replacement) in the fault groups that can be isolated using the diagnostic sequence in the current diagnostic study. The currency used for this metric (e.g., US Dollars) is listed below the "Cost to Repair" header. eXpress provides six Cost to Repair metrics:
Minimum
The Minimum Cost to Repair is the smallest cost associated with isolating and replacing all items in one of the fault groups isolated by the current diagnostic sequence. If the analyst clicks on this field when viewing the Fault Isolation Report in the eXpress report viewer, it will bring up a details report describing the fault group for which this Test limit was derived.
Maximum
The Maximum Cost to Repair is the largest cost associated with isolating and replacing all items in one of the fault groups isolated by the current diagnostic sequence. If the analyst clicks on this field when viewing the Fault Isolation Report in the eXpress report viewer, it will bring up a details report describing the fault group for which this Test limit was derived.
Average
The Average Cost to Repair is calculated by summing the costs associated with isolating and replacing each isolated fault group and dividing the sum by the total number of isolated fault groups:
where
N
=
the total number of isolated fault groups (Total Fault Groups)
FGi
=
the ith isolated fault group
CTR(FGi)
=
the calculated Cost to Repair for FGi
Expected (MCTR)
The Expected Cost to Repair estimates the Mean Cost to Repair (MCTR) that would be achieved if the current diagnostic sequence were to be employed with a fielded system. The metric is calculated by multiplying each fault group's combined isolation and replacement costs by the fault group's aggregate failure probability and then summing the results for all isolated fault groups: 
where
N
=
the total number of isolated fault groups (Total Fault Groups)
FGi
=
the ith isolated fault group
Afp(FGi)
=
the aggregate failure probability associated with FGi
CTR(FGi)
=
the calculated Cost to Repair for FGi
Differential
The Cost to Repair Differential, which is calculated by subtracting the Average from the Expected Test limit, represents how far the expected repair cost will deviate from the non-probability-weighted average. This can be a good indication of how well items or functions that fail frequently are being segregated from those that cost a lot to repair (a high positive differential Test limit indicates that they are well segregated, whereas a negative Test limit may indicate that they are poorly segregated). This metric, which was developed by DSI in the early 1990s, provides the analyst with information that may help identify the source of exorbitant repair costs. This Test limit can be calculated as follows: 
where
ExpCTR
=
the Expected Cost to Repair (defined above)
AvgCTR
=
the Average Cost to Repair (defined above)
Also included is the Cost to Repair Differential Percentage, which is calculated by dividing the Cost to Repair Differential by the Average Cost to Repair: 
where
ExpCTR
=
the Expected Cost to Repair (defined above)
AvgCTR
=
the Average Cost to Repair (defined above)
per Operating Hour
The Cost to Repair per Operating Hour is calculated by dividing the Expected Cost to Repair by the calculated system Mean Time Between Failures (MTBF): 
where
ExpCTR
=
the Expected Cost to Repair (defined above)
MTBF
=
the system Mean Time Between Failures