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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Dan Panachyda
Organization:Sensis Corporation
Date posted: Wed May 5 17:34:48 US/Eastern 2004
Subject: validity of M-Demo approach
I'm working on a project which in the past had conducted a MIL-STD-470 Maintainability Demonstration to verify a system mean time to repair requirement of 30 minutes. Now we are modifying the system by removing an entire subsystem containing some items with high failure rates and adding a few components with low failure rates. Our customer believes that as long as the MTTR for the new components is less than 30 minutes, the system MTTR remains less than 30 minutes. Our position is that this is statistically invalid because of the removal of components. Who is correct and where can I find simple explanatory documentation which can be used to justify that position?


Subject: System MTTR Predictions
Reply Posted by: Joe Dzekevich ( )
Date Posted: Thu May 6 12:51:11 US/Eastern 2004
Your system MTTR will change. When you originally calculated the system MTTR, you should have weighted the assemply, subassembly and LRU MTTRs by their MTBFs. The system MTTR is more affected by the lower reliability items. You will have to redo your system MTTR taking into account the new component MTBFs and MTTRs. MIL-HDBK-472 and MIL-STD- 470 and 471 may be helpful. Joe

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