Charles Stross referred to it as "Disaster Dominoes". Is operator error real? Yes. But a well-designed system should be resilient such that a singular operator error should generate sufficient warning to correct the error; it should not result in catastrophic failure.
Let's look at Alaska Airlines Flight 261.
Okay, so this was 25 years ago. While in flight, the MD-83 craft "suffered a catastrophic loss of pitch control". That is, suddenly the plane's nose went DOWN. Initially the stabilizer was jammed such that they had to pull up on the yoke constantly; upon successfully unsticking it, the plane went into a nosedive. They were able to mostly recover, but then experienced a further catastrophic failure which at one point resulted in them flying the commercial airliner upside down, before finally crashing.
Now, to be clear: this was not pilot error. The pilot and co-pilot did a heroic job trying to keep the plane in the air while it was experiencing severe mechanical failure. But there was a series of failures:
Out of concern for "flow" - that is, the profitable operation of the airlines - they didn't want to gum up the works with a plane turning back to LAX. I don't believe there's any certainty that returning to LAX immediately would have saved the flight, but it's worth considering, in that capitalism does apparently result in unsafe choices.
The basic design of the plane didn't have sufficient redundancy: the jackscrew assembly which controlled the horizontal flight stabilizer had two separate sets of threads, and that was considered sufficient, but in fact it still functioned as a single point of failure.
The assembly was not properly lubricated.
The assembly was not properly inspected, and they used the wrong tools to perform the inspection.
The intervals between both maintenance and inspection were extended much too long.
The FAA allowed all of these things.
The thing about this is, there were failures at every step which allowed the disaster to happen. Each mistake was supposed to have a corresponding test which would have caught it, but each of those were also wrong.
Now, it's good that the NTSB investigation uncovered these things. And that's why we need a strong, independent government which keeps companies in check.
I think too, we can guess the order in which these things happened. McDonnell-Douglas would not have designed an aircraft with insufficient redundancy if the FAA had engineers who would have caught it. Alaska Airlines would not have fabricated incorrect testing tools if there had been better oversight of the testing process. The interval between maintenances and inspections were increased when the allowed time periods were increased. They didn't become slipshod about the maintenance until after the bad testing tools went into use. In each case, the relaxation of oversight came first, followed by the relaxation of practice. [Yes, this means that Trump dismantling America's safety infrastructure will result in disasters years down the road, probably not under his administration].
One major issue with safety culture is, when it is operating correctly most of it appears completely pointless: if the maintenance is happening correctly, of course the tests will always look good. If the plane is designed well, the plane will fly fine even if the tests aren't being performed correctly. In a safe environment, you can tolerate quite a few failures before disaster happens.
And to altogether too many people, redundant safety is wasted effort.
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