MIL HDBK 217F. Today I took money to employ this obsolete, unalloyed, 100% pure bullshit.
It is what they want and they have zero interest in mending their ways.
The underlying principle of assigning a constant hazard rate to individual components and then summing it all up has no foundation in science. It hasn't become outdated - it was always utter nonsense. In fact, I know of only one degradation mechanism with an actual constant hazard rate; ionising radiation induced SEE (single event effects). Unless you are working on space, nuclear or medical systems, this aint your problem.
The standard excuses I hear when some cardigan wearing old duffer ensconced in the greasy cubicle he has occupied for the past 25 years insists that MIL HDBK 217F 1995(!) adds value:
"We have always done it like that".
"Safety department need a number".
"The customer wants it".
"We know it is conservative, but we apply a correction factor".
Believe it or not, I just came across a two orders of magnitude fudge factor. Seriously. They called this reliability engineering .
Well, I am a reliability engineer and sometimes this cretinous crap makes me wish I wasn't.
Stuff fails for one or more of three reasons: Change (degradation), variation (insufficiently mitigated by robustness) and difference (design). NOT because, perfectly randomly, "its time has come".
But there is hope, usually found under the banner Physics of Failure. Research institutions like CALCE and some medium to smaller companies outside aerospace and military actually take reliability seriously.
And please lend your support to Fred Schenkelberg and his campaign to eliminate the widespread misunderstanding of MTBF.
http://nomtbf.com/Sorry, just needed to vent.