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

A new helicopter system is under development. System failure data is collected on five helicopters during the final test phase. Failures are recorded when discovered (i.e. after the helicopters are brought into the maintenance area). Thus, exact failure times are unknown. Time is measured in flight hours and is recorded when the helicopters are brought in for service. Determine the demonstrated MTBF for this helicopter.

Problem Definition
Every two weeks, each helicopter undergoes a thorough inspection to uncover any failures that may have occurred but have not been discovered since the last inspection. Therefore, the cumulative total number of flight hours and the cumulative total number of failures for the five helicopters are known for each two week period. The total number of flight hours is 500, which accrued over a period of 12 weeks. The 500 flight hours are partitioned into six intervals, each covering a two week period. For each period, we record the total number of flight hours and total number of assigned failures for the five helicopters.

Data Entry
Using the RGA Data Type Expert, the data set is treated as Developmental Testing, Time-to-Failure Data with Grouped Failure Times, as shown next.

The data are then entered and analyzed using the Crow-AMSAA model, as shown next.

Results
The demonstrated MTBF for this helicopter is 8.78 hours. This result can be obtained using RGA's Quick Calculation Pad (QCP) as well as RGA's Plot Sheet, as shown next.

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