Forum: Reliability & Maintainability Questions and Answers

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Posted by: Ken
Date posted: Sat Aug 31 0:59:37 US/Eastern 2002
Subject: Reliability Growth Testing Mil-STD-189
Message:
I would like to ask if there is Reclassification of failures in RDGT. In RD, we allow to reclassify the failures if proven that the corrective actions are effective through further testing. Is it stated anywhere in MIL-189 that we can or cannot reclassify failures in RDGT.
Secondly, if my RDGT target is to meet MTBF of 700 hrs, what is the recommended test duration required for RDGT. Thirdly, what distribution does AMSAA model follows? (e.g exponential or weibull?) is it applicable for complex mechanical and electronic system?

Replies:
Growth Testing
B.W.Dudley Tue Sep 3 15:11:33 US/Eastern 2002

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Posted by: Ken
Organization:ST
Date posted: Sat Aug 31 0:54:45 US/Eastern 2002
Subject: maintainability prediction
Message:
DO we provide any safety factor for maintainability prediction? For e.g if i predicted 4 hours for a specific maintenace level in army context, do i allow contractor to specify the guaranteed MTTR or Mmax to be at 4.5 hours instead of the predicted value? In reliabilty prediction we are taught that predicted reliabilty must be at least 2 times higher than guaranteed reliabilty. Does that apply for Maintaninability Prediction as well?

Replies:
Maintainability
B.W.Dudley Tue Sep 3 14:32:00 US/Eastern 2002

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Posted by: Dwayne (ekimhua@hotmail.com )
Organization:DSO
Date posted: Sat Aug 31 0:48:23 US/Eastern 2002
Subject: Accelerated Reliability Demonstration
Message:
Is it a good idea to perform an accelerated RD? Originally our plan is to perform it over a span of 5 years but i intend to compressed it into 2 yrs instead so that failures can be surfaced quickly. Any comments from RD point of view? thanks

Replies:
Accelerated Testing
B.W.Dudley Tue Sep 3 14:18:48 US/Eastern 2002

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Posted by: Craig Benton (cbenton@beissd.com )
Organization:Reliability
Date posted: Thu Aug 22 15:59:43 US/Eastern 2002
Subject: Mean Time Between Unscheduled Maintenance (MTBUM)
Message:
I am trying to find a source for a full explanation of this subject (MTBUM). Could anyone direct me? Thanks ahead of time.

Replies:
Definition for MTBUM
David Dylis Fri Aug 23 16:13:26 US/Eastern 2002

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Posted by: Uma
Date posted: Wed Aug 21 9:23:43 US/Eastern 2002
Subject: Year of manufacture
Message:
The year of manufacture (used in piG calculation)is supposed to be the year the part was manufactured. Everything is normalised to 1993. But what about a part that was first manufactured in say 2001? If I buy it in 2002, it is only a year old. Shouldn't the piG for this part be much higher? If I use 2002 as the year of manufacture, PRISM gives me a much lower piG value (since it uses the 1993 normalised data). I would have assumed "delta t", the time since it was first manufactured (maturity level) would be used to calculate the growth rate.

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Year of Manufacture
David Dylis Wed Aug 21 11:37:10 US/Eastern 2002

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