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ReliaSoft's RGA - Case Studies
Software for Repairable System
and Reliability Growth Analysis

Case Study 4: Transmission Repair Data and Warranty Prediction	Software Used: RGA 6 PRO
*Download RGA 6 Example File (.rga)**

Case Study 4

This case study is based on the data given in the article Graphical Analysis of Repair Data by Dr. Wayne Nelson, published in the Reliability Edge. [Click here to download the Reliability Edge V3 I3 (*.pdf, 3158 KB)]

This data represents repair data on an automatic transmission from a sample of 34 cars. Assume that the objective is to estimate the number of warranty claims for a 36,000 mile warranty policy for an estimated fleet of 35,000 vehicles.

For each car, the data set shows mileage at the time of each transmission repair, and the latest mileage. Car 1, for example, had a repair at 7068 miles and was observed until 26,744 miles. The + indicates the latest mileage observed.

Car	Mileage (+ Latest)			Car	Mileage (+ Latest)
1	7068	26744+		18	17955+
2	28	13809+		19	19507+
3	48	1440	29834+	20	24177+
4	530	25660+		21	22854+
5	21762+			22	17844+
6	14235+			23	22637+
7	1388	18228+		24	375	19607+
8	21401+			25	19403+
9	21876+			26	20997+
10	5094			27	19175+
11	21691+			28	20425+
12	20890+			29	22149+
13	22486+			30	21144+
14	19321+			31	21237+
15	21585+			32	14281+
16	18676+			33	8250	21974+
17	23520+			34	19250	21888+

Data Entry
The Fielded Systems and Repairable options are selected in the Data Type Expert, as shown next:

Data Type Expert

The data for each transmission are entered into RGA 6 and analyzed with the Power Law model, as shown next.

Results
The beta of the power law model is estimated to be 0.3420, which indicates a rapidly decreasing failure intensity (infant mortality). This is shown in the next plot.

Instantaneous Failure Intensity vs. Time plot

The expected number of failures at 36,000 miles can be estimated from the Cumulative Number of Failures plot or the Quick Calculation Pad (QCP). Both the plot and the results obtained from the QCP are shown next.

Cumulative Number of Failures vs. Time plot

QCP

The model predicts that 0.3553 failures per system will occur by 36,000 miles. This means that for a fleet of 35,000 vehicles, the expected warranty claims are 0.3553 * 35,000 = 12,436.

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