Originally Posted by
twistedenginestarter
With MCAS, the argument is whether or not it was correct to expect the pilots to do the right things at the speed they needed to. MCAS strongly supports the proposition of automated flying, simply because MCAS doesn't work when the plane is flying automatically. The autopilot does not need any special help to cope with the evil larger engine configuration.
If you take the Max crashes and factor out MCAS, you are left with an interesting question: if the plane had been designed so that the computers were in charge: how easy would it have been to program them to cope with the sensor failures?. Inconsistent or suspicious speed etc readings can be caused by a number of system failures so would have to be a class of situations the computers could cope with.. Probably the answer to this is Boeing would have to have built in greater redundancy (ie resilience), more like Airbus do.
And more like Boeing will now have to do anyway.
http://www.b737.org.uk/mcas.htm
There was an early issue regarding how the system responded in slow flight (adding slow speed activation along with high speed pitch up conditions). There was an issue with the AOA disagree alert where it was not properly activated in all 737 Max's by all airlines. This was a contributing factor in the Lion Air accident.
For the Ethiopian accident after the pilots turned off the stab trim, cut out switches, they lost manual control of the trim wheel, so they switched them back on to regain electric trim, but this turned back on MCAS, and it's not known why they could not manually control the trim wheel.
As far as Boeing becoming more like Airbus, I think, historically, they have had different engineering philosophies, and perhaps an issue here is Boeing is trying too hard to be like Airbus. They are very different aircraft. They are not the same style or engineering practice.
Here is a salient quote " During
The House Committee on Transportation & Infrastructure hearing in October 2019, an email exchange was disclosed between Boeing employees from 2015 which read: "Are we vulnerable to single AOA sensor failures with the MCAS implementation?" The response from CEO Dennis Muilenburg was that the email showed that "our engineers do raise questions, in an open culture," but that the single-sensor design met the standards. John Hamilton, chief engineer for Boeing’s commercial airplane division, who testified alongside Muilenburg, said that single points of failure are allowed in airplane design depending on the hazard assessment. Any dissent the committee could present on the final assessment that a single sensor was merited “highlights that our engineers do raise questions and it’s an open culture.”
The final KNKT investigation report into the
Lion Air accident said as a contributing factor "The replacement AOA sensor that was installed on the accident aircraft had been miscalibrated during an earlier repair. This miscalibration was not detected during the repair." the angle it registered was 21 degrees too high. Following the publication of this report, the FAA revoked the certificate of approval of Xtra Aerospace of Miramar, Fla., the company that supplied the faulty AoA sensor. Xtra subsequently issued a statement saying that “we respectfully disagree with the agency’s findings.” It added that the revocation of its certificate “is not an indication that Xtra was responsible for the accident.”
Again sensor issues have become more common-place and this needs to be addressed as well even if everyone is trying to avoid responsibility. More significant redundancies perhaps--but, maybe MCAS itself was a mistake to gain longitudinal stability. That takes more digging.