OK, I am going to comment, as a certified and practising functional safety engineer with a TUV number and experience designing and building industrial systems to IEC61508 (functional safety parent standard) and IEC61511 (process industries).

Functional safety is the engineering discipline related to designing machinery instrumented safegaurding systems to protect humans from harm, to a deterministic safety performance level.

eg just the right amount of safety so that all the safety money is spent in the right places and right amounts so as to reduce risk across the board to the required level, not over-investing in one area and neglecting another (or so the dream goes, in practice it is a moving target based on a lot of guesses, you hope the swings and roundabouts balance out more or less).

Aeronautics design is one of the closely aligned fields within the group of this overall discipline. Closest thing I have worked upon in terms of risk/consequences is mine winders - safety failure can kill 10-100 people in one go, they ride multiple times every day.

Right now, this very minute before needing a break at 1am to browse hacker news, I was trying to wade thru a mess of a fault tree analysis my current project owners "specialised" consultant has produced for the systems I currently need to instrument for safety.

Most people in general, but especially Americans who live primarily with prescriptive standards, struggle to come to grips with the nature of performance based safety standards. There is no "do it like this and you have met code and have no problems" - you have to analyse and build everything up from scratch.

It is all about layers, layers of risk reduction that eventually (whether by perception or reality) get the risk down to an acceptable level. So there are cludgey little things that get stuck on as hacks to address this issue or that, not uncommonly often pet issues of one of the review panel. Repeat this several hundred or thousand times and any hope of some kind of uniformly elegent and simplified solution is pretty slim.

The general reliance is on redundancy and independence,
eg layers of protection, "defense in depth", or as more commonly known "the swiss cheese model" - you get a bunch of slices of swiss cheese and when the holes line up to allow a path through, that is when an accident can occur. More layers, less chances (also smaller holes, but that is another story again).

And, as almost always, the machines are actually the easy part most of the time. It is the humans that design, build, test, maintain, certify the machines that are the weak point, over and over again. Plus the creative ways humans can get around systems in place to protect them, get their job done when the system is telling they should stop, or doing a maintenance task a new "better way" despite the manual that might have cost over $100k plus of engineering time to write and approve is telling them to do it a specific way etc etc etc

90% of the time overly conservative thinking during risk analysis occurs (we might get hit by a meteorite, happened to my cousin once), which can layer complexity and associated uncertainty and poor availability onto a solution.

10% of the time there is the wishful thinking of "it will never happen because I have never seen it or heard of it" that allows the unexpected and unusual (black swans often, if you will) to sneak through, at least for the first time. Endless discussions occur about "credible scenarios", sometimes the "discussion"is won by the dominant personality in the room, who might also be doing some of the pay reviews next month.

It is incredibly difficult to be the person that has to herd the flock of cats that represent all the stakeholders in a hazard revue and risk assessment. These workshops sometimes run for months, maybe in extreme cases for years on and off, considering every system, subsystem, part, action, event, procedure etc etc and all the possibilities and how they can go wrong and what might mitigate failures and events - and on and on.

I could write about this all night, but I guarantee you that any magical opinion or assumption you might have about graceful and elegant solutions to difficult and dangerous problems being the norm are unrealistic - there is a always a consensus or committee to satisfy, often top heavy with people that might have to own or operate the machine in question, but never designed anything in their lives. You fight for the things you know matter and concede some of the crap, hoping subsequent reviews will see it as pointless or not credible.

All of this is the reason that grandfathering is so attractive. To apply the current internationally recognized performance based safety standards from scratch to design something as complex as a plane that can kill hundreds of people in one go is an incredibly difficult task. And from a business perspective fraught with immense dangers of totally unpredictable outcomes impacting budget and schedule and even viability.

This is a highly specialised field with what are often counter-intuitive outcomes (otherwise you would just let John out the back room design the whole plane from scratch, because "he knows what he is doing").

While I am aghast at some of the information about some of the information about design decisions taken that is emerging, none of it surprises me in the least. I can see directly how a number of them may have effectively resulted from path of least resistance when a product had to be produced.

I like flying older planes in general, as long as the airline does reasonable maintenance. The unexpected has often been detected and corrected, the chances of latent faults turning up decrease with hours in service. Plus I always remind fearful daughter that the taxi ride to the airport is more dangerous, by the numbers.