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I think the answer to this question is no, because I cannot find it in the PDF, but I'd like a more expert opinion.

The reason I'm asking is the assumption that if it was, its malfunction could have been remedied by switching to the redundant "side" (perhaps as in pilot/copilot systems redundancy), along with a correctly functioning angle-of-attack sensor (the one that didn't break).

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It does not appear that MCAS was in any of the maintenance documents. This was part of the issue with the Lion Air crash. On the previous flight with the accident aircraft, MCAS acted on the faulty sensor data, but the pilots used the trim cutout and completed the flight. They had no reason to suspect that a trim issue could be related to a faulty AOA sensor, so just the warnings for IAS and ATL DISAGREE and FEEL DIFF PRESS were logged for maintenance. As you noted, if they had known the connection, they might have diagnosed the true cause and either replaced the AOA sensor or MMEL'ed it. Instead they focused on the Air Data Module and elevator feel computer. It wasn't until a couple weeks after this crash that Boeing sent a message to operators describing MCAS.

It's also unlikely that the MMEL would have allowed MCAS to be completely disabled. This would have required extra documentation and possibly training for the pilots on how the plane would handle differently without it. This additional training is what MCAS was designed to avoid, and would have defeated the purpose of having it in the first place. Also, if it were that simple, it seems like they would have taken this step rather than grounding the entire fleet.

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  • $\begingroup$ And speaking strictly about the redundancy of the MCAS system itself (where the "system" is MCAS and one Angle Attack Sensor connected to it) -- was there a redundancy (2 MCAS units, each connected to one side's Sensor) or not? $\endgroup$ – youurayy Jul 27 at 0:03
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    $\begingroup$ @youurayy. no, there was no redundancy at all. The system itself is only a protection, so it isn't required to be redundant. The problem was that it was not sufficiently secured against improper activation. $\endgroup$ – Jan Hudec Jul 27 at 22:11
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    $\begingroup$ I understood the factual report not as saying MCAS wasn't mentioned at all, just that the troubleshooting checklists were insufficient. They even mentioned the AoA probe for at least one of the reported faults, but the mechanics had a “spurious success” on some of the checks that lead them to conclude they found and fixed the issue and end the maintenance without getting to test the AoA probe. $\endgroup$ – Jan Hudec Jul 27 at 22:19
  • $\begingroup$ @JanHudec would you say that was the biggest fallacy of this case - not treating a system which can bring down the plane if it acts erroneously (not just due to a faulty AoA but e.g. the system itself misfiring, e.g. software or hardware fault in the MCAS logic itself) - as not needing redundancy? $\endgroup$ – youurayy Jul 29 at 1:11
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    $\begingroup$ @youurayy, no. The biggest fallacies were underestimating dangerousness of it's failure (fail-active due to bad input) and failure to realize impracticality of the only provided backup (the ET-302 did initially cut off the electric trim, but were unable to adjust it manually, so they turned the electric trim on again to try something else, which they didn't manage for reasons not yet fully analysed). $\endgroup$ – Jan Hudec Jul 29 at 18:43

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