Oddbean

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 @48bfa577 
I was in maintenance for almost 40 years. At one time, my title was Manager of Maintenance and I covered all the states west of the Mississippi River. 
Things have changed in the last 15 years or so. I blame how engineers are educated. The Just in Time warehousing, efficiency planning, cost benefit analysis  - all designed to maximize near term profits. It was one of my motivations for early retirement. Maintenance of critical equipment requires a different thought process.

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 @602e6fbe We can't use much of modern supply chain management techniques. The reason for this is that the stuff we build is electronic and has to be maintained and replaced for 20-40 years. It also has a 5 year development cycle and the build contracts last 5 to 6 years. So by the time we are shipping units they already contain many obsolete parts, let along 40 years down the road.

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 @48bfa577 
Reliability as a primary goal is not focused on cost effectiveness. Cost effectiveness often happens when you get it right, but the measurement of it is difficult. If you have no unplanned outages, how do you prove cost-benifit on your maintenance cost? All of your cost of unplanned outages is theoretical- so the engineers don't apply much weight. So, maintenance budgets are cut, and profits go up..... for a while. Then things start to break.

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 @602e6fbe we use some hocus pocus to measure this stuff. To go from 90% reliability after 10 years to 99% costs more than going from 60% to 90%. So we evaluate that cost compared to the cost of down time and replacement for each item. If it's safety equipment no cost is considered, we go for maximum reliability (parts with failure rates of parts per million, but if it's something cheep and just used for advertising or of low consequence in the event of failure, we do parts per thousand.