SRC Forum - Message Replies
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
Posted by: Dave Fetters
Date posted: Thu Jan 13 12:00:16 US/Eastern 2000
Subject: MIL STD 471 - M. Demo
I'm planning a Maintainability Demonstration. There are MTTR and MaxTTR requirements at each of 3 levels of maintenance. I wanted to use Test Method 8 in MIL-STD-471A in hopes of avoiding 50 observations on 6 different specifications (which the other methods seem to require). However, the DS-level MTTR spec. is 2 hours (greater than the 100 minute limitation called out in the second paragraph of the method). I can't figure out how important that 100 minute limitation is. In other words, is it possible to "cheat" by 20 minutes, or is there a workaround for longer MTTRs? Anybody know?
Subject: Maintainability Demonstration
Reply Posted by: Bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Tue Jan 18 9:25:34 US/Eastern 2000
Mil-Std-471(Maintainability Verification and Demonstration), which has been replaced by Mil-Hdbk-470A, indicates that the mean time interval to be tested should be "greater than 10 and less than 100 units of time" for test method #8. This is not a specific requirement for "minutes" it could be considered to be "hours" or "minutes and hours". I do not believe that a test using 120 minutes as the mean and 240 minutes as a maximum will causes any problem with the sequential decision matrix.