PRISM Forum - Message Replies
Topic: PRISM Questions and Answers
Topic Posted by: SRC
Date Posted: Wed Jan 12 8:33:33 US/Eastern 2000
Topic Description: Welcome to the PRISM forum! Please feel free to post your questions and comments about the PRISM assessment software here.
Posted by: don miller
Date posted: Sat Dec 8 18:38:35 US/Eastern 2001
Subject: random geneic hardware failure rate
30 +years at Boeing. first 10 big hero in OR. logistic analysis , Otimum spares provisioning. I did it all. I had 3 years at TRW 1969 -1972. had the chance to review the basic notion of random failures. Back to Boeing. worked MM AWACS B1 guess what never found a ransom failure which met the criteria for inclusion into MTBF prediction effort. Finally (like Einsten who took 7 years to get rid of wrong ideas)I wised up. Have sound data which shows that any notion of predicting frequency of hardware failures is absurd. Wearout is ok. Failures occur (big time in early MM). However they are virtually always related to design problems, human error, manufacturing problems ect. Please help us rid the aerospace industry of this triva. Or any other foolish folks .I have seen a few MTBF statements on PC. Not many.
Subject: Reliability Prediction Pitfalls
Reply Posted by: Michelle Li
Date Posted: Fri Jan 10 9:55:47 US/Eastern 2003
Don and Kirk:
I have been in reliability area just for 5 years. I have done predictions (217, PRISM, field data)and RET. When I recently evaluate PRSIM for my company. My recommendation was to use it with sound judgement. My comment was that reliability prediction was total waste no matter what method you use. I just simply wish that people will realize that and quit using it. (I thought I was the only one for this opinion. By the way, I think that RET is a way to go to improve reliability in real world.
Another thing bothers me even more: safety analysis is based on reliability prediction results. FAA has detailed requirements, for example, in Part 23, the probability of misleading altitude information per flight hr must be less than 10-7. This number can be derived by Fault Tree Analysis. But the foundation of the FTA is the failure rates of possible failure events. If the reliability predictions are nonsense, how much we can trust the safety analysis results.
FMECA is also based on reliability prediction results.
Don and Kirk, do you have any comments on safety analysis and FMECA which use reliability prediction results as the foundation?
Thank you very much.