MTTFF or MCTFF for a single nonrepairable component

[Eugene Cottle]

I am sitting in on a discussion on the preparation of an industry standard, and there are some questions about definitions, examples, equations, etc. We have an example showing the calculation of MCTFF based on a given 2-parameter Weibull distribution. In this context, for a single, non-repairable component, I'm not sure whether the calculation is even meaningful, i.e, what does the "first failure" mean for a single, non-repairable component. Also, I am having a hard time finding a reference to verify the equation (no reference is given in our example). The equation used is MCTFF=x0+(eta-x0)Gamma(1+(1/beta)), where eta is the characteristic life, beta is the shape factor, and Gamma is the gamma function. I believe x0 refers to the first failure, although that isn't really clear.

[tarik]

What does MCTFF mean? I googled it and didn’t find much about it.
If you are talking about an unrepairable system, the mean time to first failure (or simply the Mean or Mean time to failure MTTF) can be found at: http://www.weibull.com/LifeDataWeb/weibull_statistical_properties.htm (for a 2-parameter Weibull, just replace the gamma parameter with 0). You are right to be confused about the meaning of “first” failure for an unrepairable component. That’s why Mean or Mean Time To Failure (MTTF), Mean Time Before Failure (MTBF) would be a better metric name

[Rui Assis]

MTTFF is an acronym found in the literature related to reliability, to express time to first (and the unique) failure of non-repairable items such as components pertaining to satellites (once in space), missiles (once in air), munitions (once fired), and so on. For repairable items MTTF is used instead.

MCTFF never heard, but I would like to learn its meaning, although I suspect MCTFF and MTTFF mean the same.

[Rui Assis]

Correction to my previous post:

...munitions (once triggered),...

[Eugene Cottle]

I found the acronym and calculation in the documentation for Blocksim. Blocksim output results show a calculation for the first failure of a system or population. Intuitively it makes sense, for the first failure to occur in one component or the earliest failure in a population. The equation is basically the same as that for MTTF, but includes the x0 term.
MCTFF would just refer to Cycles rather than Time, no real mystery there.
In the context of a missile or satelite, how would the Mean Time to First Failure differ from just a Mean Time to Failure?

[tarik]

If you are considering the missiles as one-shot systems, meaning they don’t operate for some time before they fail, they either work or not work upon request? In that case the MTTF doesn’t apply there.

If you are considering the Mean Time to Failure to be the Mean time Between failure, considering this is a repairable system, then Mean Time to Failure = Mission Time/Number of Failures.