Originally Posted by
PEI_3721
The NG could be a simple logical argument, fails to meet requirements, ground the aircraft until improved. However, an ‘emotional’ but logically inaccurate argument based on ‘no accidents so far’, could allow the aircraft to remain in service, although the risk of failure is the same.
This choice has potential for splitting the regulatory authorities, purist vs practical, but could be managed with compromise. Everyone might wish to avoid using the piloting contribution in recognition and inhibition as a permanent solution.
If the NG is easier to recover than the MAX (effect of aero differences), then it could be argued that alleviation with pilot recognition and action to mitigate risk could keep the aircraft flying until the trim system is modified. There may be similar contributions from restricting wt, cg, and of course lots of training.
If the NG is more difficult, then the industry faces a pivotal point in certification and risk management, where short term compromise could be based on definitions of safety, ‘what we are doing’ vs ‘what we have’, and of course timing of modification.
The critical factor depends on who makes the decision and how is this presented; not Boeing, ideally FAA in conjunction with (all) other authorities; but then few things are ever ideal.
Despite all the angst relating to the 737NG family, it should be acknowledged that it has amassed one of the best safety records of any commercial aircraft every built. To Boeing's credit, the stab trim system (pre-MCAS) had been so incredibly robust and reliable that many airlines became complacent and simply stopped training adequately for its possible failure modes.
This highlights an interesting problem relating to the overall level of safety of complex systems. I recently read an interesting book by Malcolm Gladwell titled "What the Dog Saw", a collection of articles that were previously published in
The New Yorker magazine. In one section, Mr Gladwell discussed various forms of failures (business, intelligence, safety) that seemed incredibly obvious in retrospect. He rightfully asks how so many people could miss things that were so "obvious"?
One problem is that human beings are frequently subjected to massive amounts of data that are conflicting and ambiguous, and it is only after the fact that we are able to properly discern which of the data was pointing to the problem. From what we know so far of the MCAS debacle, it appears that numerous individuals made decisions that, in the context of their particular view of the problem, seemed reasonable at the time. It was only after the sum total of those decisions came together at a certain place and time that the systematic failure became obvious.
Another counterintuitive problem arises when steps taken to improve overall risk of a system fail to do so because of a change in behavior induced by those very improvements - a phenomenon known as risk homeostasis. Mr Gladwell gives an example of a study conducted in Germany when antilock brake systems (ABS) were being introduced. Half of a fleet of cabs had ABS installed, and the other half retained the old style brake system. The drivers were then monitored for three years. Contrary to expectations, the ABS-equipped drivers had
worse accidents records than their counterparts without ABS. Why? The investigators determined that the drivers with ABS systems took greater risks. They drove faster in wet conditions, they made sharper turns, they were more likely to tailgate, etc. In effect, the drivers were "consuming" the risk reduction by increasing the riskiness of their driving behavior.
I would submit that there is a similar phenomenon occurring in aviation. As manufacturers fielded demonstrably safer aircraft, airlines compensated by producing less proficient pilots. Whether this phenomenon was fully appreciated at the design engineering level is not entirely clear. However, in regards to the MAX accidents, Boeing was apparently expecting the pilots to be more skilled than they actually were, and the airlines were expecting the aircraft to be more resilient than it was. Each side made assumptions regarding the level of risk inherent in their choices based on their perception of the level of risk maintained by the other.
I suspect that risk homeostasis will continue to be an issue in aviation. Manufacturers and airlines are profit-driven entities, and their will always be a temptation to be less vigilant toward their individual contribution to a safer system if they
perceive (rightly or wrongly) other factors are increasing the level of safety.