Trying to Respond to All Questions and Comments Concerning MTBF

Over the past couple of days, like most days, have received questions and comments concerning MTBF. I do try to respond to all questions and acknowledge the comments.

Glad to help in anyway I can, so please feel free to send me your questions. Certainly do appreciate the supporting comments, or any comments for that matter.

Let’s take a look a few such discussion that occurred over the past two days. [Read more…]

How We Think About Reliability Is Important

Getting on an airplane we think about the very low probability of failure during the flight duration. This is how we think about reliability.

When buying a car we think about if the vehicle will leave us stranded along a deserted stretch of highway. When buy light bulbs for the hard to reach fixtures we consider paying a bit more to avoid having to drag out the ladder as often.

When we consider reliability as a customer does, we think about the possibility of failure over some duration.

And, we really don’t like it when something fails sooner than expected (or upon installation). [Read more…]

Is MTBF Preventing Your Product From Being Reliable?

MTBF is not reliability. Attaining a specific MTBF does not mean your product is reliable. MTBF use may be the culprit.

Therefore, working to achieve a MTBF value may actually be preventing you from creating a product that mets your customer’s reliability performance expectations.

Actively working to achieve MTBF using the common tools around MTBF may be taking you and your team down the wrong rabbit hole. You may be working to reduce the reliability of your products rather than improving them.

Let’s take a look at a couple of ways the pursuit of MTBF is harmful to your product’s reliability potential and contrary to your customer’s expectations. [Read more…]

Despite standing for the ‘time between failures’, MTBF does not represent a duration. Despite having units of hours (months, cycles, etc.), it is not a duration-related metric.

This little misunderstanding seems to cause major problems. [Read more…]

Now for something completely different. Roaming the net looking for an interesting advertisement or data sheet with a ‘great’ (i.e. bad) example of the mis use of MTBF, ran across that MTBF is actually being used by at least one government for department budgeting.

by Mark Powell

Most of us have seen reliability specified using a requirement like the following:

The Zeus 5000 SUV shall have an MTBF of 144,269.5 miles with a 90% confidence.

Some readers may not have seen reliability requirements specified in any other way.  What they have always seen has read something like:  The widget shall have an MTBF of X with a Y% confidence.  This reliability requirement structure is rather ubiquitousin military and aerospace specifications, which along with Mil-HDBK-217, have been major influences in reliability specification practices for decades in many industries.

After a discussion with a client this morning, and their motor vendor’s reliability engineer asked for a reference for a sample size calculation formula I recommended, I had a short email exchange with said reliability engineer. In my note with the references, I included an aside with a link to this site. He liked the site and agreed that MTBF was often misunderstood and not useful. He asked if the store sold much in the way of NoMTBF logo’ed merchandise – it doesn’t btw. I thought about how and why this site and the store exist and that invited my passion on this topic once again.

We need to do something to further the eradication of MTBF.

[Read more…]

[updated January 2025]

Just answered a question on where to find reliability engineering training on basics and statistics. There are plenty of options and below I’m listing just where to find the many, many options available to you.

When Asking for Reliability Information, Do You Ask for MTBF?

Our customers, suppliers, and peers seem to confuse reliability information with MTBF. Why is that?

Is it a convenient shorthand? Maybe I’m the one confused, may those asking or expecting MTBF really want to use an inverse of a failure rate. Maybe they are not interested in reliability.

MTBF is in military standards. It is in textbooks, journals, and component data sheets. MTBF is prevalent.

If one wants to use an inverse simple average to represent the information desired, maybe I have been asking for the wrong information. Given the number of references and formulas using MTBF, from availability to spares stocking, maybe asking for MTBF is because it is necessary for all these other uses. [Read more…]

MTBF is a symptom of a bigger problem. It is possibly a lack of interest in reliability. Which I doubt is the case. Or it is a bit of fear of reliability.

Many shy away from the statistics involved. Some simply do not want to know the currently unknown. It could be the fear of potential bad news that the design isn’t reliable enough. Some do not care to know about problems that will require solving.

Whatever the source of the uneasiness, you may know one or more coworkers who would rather not deal with reliability in any direct manner.
[Read more…]

To me it means very little, as it rarely occurs. Products fail for a wide range of reasons and each failure follows it’s own path to failure.

As you may understand, some failures tend to occur early, some later. Some we call early life failures, out-of-box failures, etc. Some we deem end-of-life or wear-out failures. There are a few that are truly random in nature, just as a drop or accident causing an overstress fracture, for example. [Read more…]

Just back from the Reliability and Maintainability Symposium and not happy. While there are signs, a proudly worn button, regular mentions of progress and support, we still talk about reliability using MTBF too often. We need to avoid MTBF actively, no, I mean  aggressively.

Let’s get the message out there concerning the folly of using MTBF as a surrogate to discuss reliability. We need to work relentlessly to avoid MTBF in all occasions.

Teaching reliability statistics does not require the teaching of MTBF.

Describing product reliability performance does not benefit by using MTBF.

Creating reliability predictions that create MTBF values doesn’t make sense in most if not all cases. [Read more…]

MTBF use and thinking is still rampant. It affects how our peers and colleagues approach solving problems.

There is a full range of problems that come from using MTBF, yet how do you spot the signs of MTBF thinking even when MTBF is not mentioned? Let’s explore the approaches that you can use to ferret out MTBF thinking and move your organization toward making informed decisions concerning reliability. [Read more…]

Over 20 years ago the Assistant Secretary of the Army directed the Army to not use MIL HBK 217 in a request for proposals, even for guidance. Exceptions, by waiver only.

217 is still around and routinely called out. That is a lot of waivers.

Why is 217 and other parts count database prediction packages still in use? Let’s explore the memo a bit more, plus ponder what is maintaining the popularity of 217 and ilk.

Why do we use ReliaSoft instead of JMP to Identify the Time to Failure?

This is a question someone posted to Quora and the system prompted me to answer it, which I did.

This question is part of the general question around which software tools do you use for specific situations. First, my response to the question. [Read more…]