On failures, found this interesting but quite long and detailed report on ski lift inspection and maintenance:
It's quite detailed and scholarly, so I don't know whether I'm reading it right, but Table 33 on p. 43 says MTBF for sheave wheels is 25 days, and for Bolts & Connections is 29 days. Does that mean each and every sheave wheel and bolt typically needs to be replaced every 25 or 29 days respectively, or do you think that's 1 failure for any wheel or bolt on the entire line?
Can't be for individual components. System-wide, it makes sense, though, which is why the paper argues for more frequent inspection intervals.That's what it says, although that seems pretty short to me.