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: Tim Daniels
Date posted: Tue Oct 26 10:09:55 US/Eastern 2004
Subject: Spares level over set period of time
Sorry this may be a silly question but it's the first time I've done anything like this.
I need to calculate the number of spare LRUs required for a product to have 95% confidence level (of having a spare available) when the repair time is 10 months. I have failures/million hours figures and thought the RAC Poisson calculator for sparing was the answer! But now I have to consider a mission time of 18 months and calculate spares for this time only. I cannot see what will change. Can anybody give me any clues?
Any ideas will be very much appreciated.
Reply Posted by: John Cloarec
Date Posted: Wed Oct 27 4:20:19 US/Eastern 2004
Hello Tim, the calculation for 10 months gave you the quantity of spares you need to achieve the mission.
For 18 months you will calculate a new quantity higher than for 10 months, that's all !!!
This means that for 10 or 18 months you will not buy extra spares (you will use only the spares you've bought at the beginning of the mission) and that the probability to achieve your mission is 95%.