> If you know what's going on, MCAS is quite safe - there are two highly visible switches that kill electric trim completely (thus disengaging MCAS) and allow the pilots to take manual control. Activating these switches is a memory item (i.e. pilots have to memorize the checklist) for runaway trim and would be universal across 737 variants.

> Unfortunately, it appears that both the Lion Air pilots and the Ethiopian Airlines pilots did not recognize that this was a runaway trim issue at all (or until it was too late). If the Ethiopian Airlines disaster turns out to have an identical cause to the Lion Air crash, one has to question why the pilots did not take this simple corrective action.

Not quite:

While the runaway trim checklist is a memory item, the symptoms that pilots train on in simulator presents runaway trim as a continuous event (the "classic" runaway trim being a relay becomes stuck and the trim just extends continuously).

So while they've trained on the correct response to save the plane, they've never actually been exposed to the symptoms that an "MCAS runaway" presents (stick shaker on the AOA too steep side when the plane is patently not in stall combined with speed warnings and an uncommanded nose-down that goes away for several seconds when the stick is pulled back).

The "backs off" part is critical when combined with the speed warning alerts and lack of continuous trim, because this makes the nose down easy to interpret as coming from the 737's speed trim system, which has existed for decades, and the net result is that the combination of symptoms seems to overload/confuse the pilots.

We have, now, at least 3 documented examples of "MCAS runaway" -- the two downed flights, and the prior Lion Air flight in which a deadheading pilot in the jump seat did suggest to cut the automatic trim, but ONLY AFTER several minutes of confusion in the cockpit. And even after disabling it, they re-enabled the auto trim initially and only re-cut it out when symptoms re-occured.

Which all boils down to: The MCAS system is in no way "quite safe". Safety is not a single line of defence, and the fact that at least 3 sets of pilots have struggled to identify the correct response to the MCAS issue indicates that the design of the system is flawed, because no system is safe when its sole and only fallback relies on humans 100% providing the correct response to a never-before-seen set of symptoms.