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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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Posted by: Stephen Deneca ( )
Organization:Honeywell Aerospace
Date posted: Tue Apr 9 16:03:22 US/Eastern 2002
Subject: Field MTBF
I am a member of a team that is trying to find a way to calculate MTBF for products in the field. We know that our Repair stations only see about 5% of the total repairs done to our product and the rest are private repair stations that do not report back to us. We are tied into ACAS from which we can get our total number of units and total flight hours for all of our products in the field. Does anyone have any suggestions as to how we can relate the two pieces of information together?


Subject: field MTBF
Reply Posted by: Klaus Denkmayr
Organization: AVL
Date Posted: Mon Apr 15 10:33:22 US/Eastern 2002
We have a similar situation with our measurement equipment and do it this way: Two scenarios: 1) If a certain subset of your products is repaired exclusively by your crew, the only thing to check is whether the usage profile for this subset is representative for all of the products. If so, the MTBF of the subset is a good estimator for the overall MTBF, if not, a correction factor has to be determined to account for the usage deviation. This requires an investigation of typical usage conditions of items both repaired and not repaired by your service crew. 2) If customers use for one and the same product sometimes their own staff and sometimes your repair crew depending on the failure mode, the situation is more difficult. I would recommend to concentrate on a few customers with good relations and convince them to share their repair data. In our case this works. Regards Klaus

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