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Scatter Factor
2

Scatter Factor

Scatter Factor

(OP)
I have a requirement document that states "no major fatigue damage thru a 25500 flight hour / 17000 flight cycles for economical life, minimum scatter factor of 4"
Does this mean that I need to test to 4 times the life, ie 4*25500 hrs or 4*17000 cycles?  And do I also need to factor my fatigue calculations to show a factor of 4 on hrs/cycles?

RE: Scatter Factor

yes, no ...
fatigue calcs (you know, looking up an s/n curve at your stress) determine the "unfactored" life (so "no" factoring).
but your requirement is for a safe (or factored) life of 25,500 flights, so with a SF = 4 , your calc will need to have an unfactored life of >102,000 flights (so "yes")

RE: Scatter Factor

TDI

First of all, the requirements will depend on whether you are certifying to Part 23 or Part 25. If its Part 23, the new document to use is AC 23-13A. The AFS120 is no longer current. Also, if Part 23, are you certifying to 571(a),(b) or (c)? This will affect the factor used. AC 23-13A has a detailed explanation of the various methods and it is what the FAA currently uses for all new programs. If Part 25, normally all safe life certified items use a minimum of a factor of 4 but AC25-571 and AC91-56 will provide some guidance as well.

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