The Reliability Metric: A Quick and Valuable Improvement Over MTBF

By Fred Schenkelberg in Reliability Engineering Management

130 pages, published 5/25/2015

This short book explores reliability metrics including MTBF and reliability. The choice to avoid using MTBF and switch to reliability should become obvious. Understanding our metrics and the behavior they promote allows reliability professionals to speak clearly and improve reliability performance.
Note: Soon to add Amazon and iBook versions. MagCloud provides print on demand and pdf versions.

13 thoughts on “Books

  1. How to perform the reliability activities(RBD,FMEA and FTA), If the bill of material for a product is not available?

    1. I had to read the question a few times. I generally do RBD, FMEA and FTA without a bill of materials. All these tools provide value at the system or functional level. Including functional blocks or subsystems and you can and should get started with these three tools.

      How to do it… RBD – system and subsystems can be arrange in the model and initial goals or estimates provide the necessary information to make early concept decisions.

      FMEA – focus on system or functions

      FTA – again focus on critical functions – addd more detail as necessary as additional information about the design become available.



    1. I would use the definition of reliability to define the concept.

      The reliability of the new product shall

      provide xyz function(s) (see the product requirement documentation for the full set of functions)
      within the xyz set of environmental and use conditions (weather and how often used, etc.)

      with probability of successful operation (i.e. without failure) of xyz

      over specified duration.

      Of course you can set more than one probability and duration – say one for out of box, one for the warranty period, and one for the expected duration of use. The specifics would be tied to business and customer requirements.



  2. 1. At the early design stage of a product (like Aircraft engine), what are the reliability activities are required to perform ?
    2. Basic activities like RBD ,FMEA and FTA are already performed for the aircraft engine.

    Available inputs

    1. BOM.
    2. Design/functional document.
    3. Engineering drawings.
    4. Test data.

    Kindly do the needful.

    P.Madhu sudana
    Reliability engineer.

  3. Dear Fred,
    Have a good day!!
    A challenge in-front of us that the reliability approach for single shot item need to demonstrate.

    Pls suggest any references for the same.


    1. All the basics of reliability engineering apply with the constrain of a single use mission…. Let’s say this is an inexpensive medical device, you can quickly demonstrate using many devices the ability to the systems to operate successfully. If a large expensive item (rocket, for example) then testing a bunch of full systems is not practical. So break it down to subsystems and focus on critical elements. the risk is in the interfaces that appear in a full system. Modeling, analysis, and characterization work become much more important.

      Same basic references along with a bit more creativity on building your team’s understanding of how the system performs.



      1. Hi Fred,
        How to control the vendor specifications after 4 years of product released. Also how cost involved for the product once change in specifications.

        1. Good topics and questions Viswanatha – the short answer is for vendor specifications it is common practice to trust and verify – trust your vendors and check what you receive on occasion.

          The second part about cost and product changes – not sure I understand the question… cost is likely to change and that is between you and the vendor.



          1. Hi Fred,
            Usaully FRACAS is failure reporting analysis and corrective action system but how to distinguish 8D process and DAMIC cycle with FRACAS.

            Also please clarify if anything term called DMEA in reliability…


  4. Hi Viswa,

    8D is focused on root cause analysis which is a common step when dealing with something logged into a FRACAS system. 8D using a number of familiar tools, like 5 whys and DMAIC (plan do check act cycle) within the process of sorting out and solving problems.

    DMAIC is a simple approach to continuous improvement or with any project to make a change to a system product. When we find a fault or failure we often address it by making a change, DMAIC is one approach and often useful approach to set up and monitor the change.

    I’m not familiar with DMEA, do you mean FMEA or Design FMEA (DFMEA)? If it’s FMEA we use it in reliability work to identify and prioritize the most important faults or failures to address/mitigate within a development process.



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