MILSTD2173

[A. Rowland]

If anyone has experience with MIL-STD-2173, I am curious about the equation for acceptable failure probability found on page 47. This equation uses 0.5 failures in the numerator. Is there a basis for 0.5 and, if so, what is it?

[Relman]

As it says in the text above "0.5 failures over the life is acceptable to obtain a finite probability". If you used zero, that would give an infinite result, and using 1 assumes that there will definitely be a failure during the life of the fleet.

In other words, set the probability of failure during the lifetime at 50% - either there will be a failure or there won't - and calculate the acceptable number due to safety critical and Cat I or II failures.