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: Randolf
Date posted: Mon Mar 5 15:50:23 US/Eastern 2007
Subject: Failure Rate to Probability of Occurrence per Flight Hour Conversion
Can anybody tell me how to convert a failure rate (obtained from MIL-217 etc.) into a Probability of Occurrence per Flight Hour ?
Subject: Convert calendar failure rate to operating hour failure rate
Reply Posted by: Larry George
Date Posted: Mon Mar 5 17:23:31 US/Eastern 2007
The Air Force Logistics Command inspired “Convert From Calendar to Operating Time Reliability,” ASQ Reliability Review, Vol. 18, No. 3, Sept. 1998. The motivation for that article is described in //www.fieldreliability.com/NWSLT3.DOC starting on page 6.
The graph on page 7 of aircraft operating hours per month shows why rescaling the MIL-HDBK-217 failure rate is inappropriate. Some planes are hangar queens and hardly fly, while others fly a lot more than average. Could the flight planners have chosen aircraft with fewer hours to fly more? The point is that different aircraft fly the different hours per month and that increases the variability of failure rates, which in turn increases spares requirements.
Contact me if you want the article or free samples.