Yeh. Think I made that point earlier based on such a blatantly naive solution to an Alpha ~ Stick force condition, messing so brutally with stab trim.

Literally, we seem to have a black and white mandatory certification requirement, ignored or overlooked by the project engineers who postulated moving these large engines up and forwards, developing into a mad rush for an affordable workaround... to a situation that would RARELY be met; would be UNDERSTANDABLE to a crew if it was; and could be ANSWERED COMPREHENSIBLY by a pre-existing and time-honoured stick shaker (or re-engineered shaker/ pusher pair)

I'm no systems whiz. Just trying to generate some empathy for the tech crews in these scenarios.

Wasn't the problem with that, that - with the new bigger engines attached to the old wings - the elevator alone is too small to begin with to come to the rescue in a perceived approaching stall scenario, particularly at high speed at altitude scenarios, and that a redesign of the tail section was to be avoided, to save money and time?

Also, as far as we know, MCAS itself might have worked as intended, had the single AoA sensor it depends on not acted up. The problem apparently is, that against fundamental state of the art aerospace engineering principles, it was designed without redundant sensor data input, thus making it irregularly vulnerable as a system, that in case of malfunction potentially leads to outcomes in the "catastrophic" category.

Anyway, the jackscrew was found in the HST full nose down position, and it's highly unlikely the pilots put it there. Pilots and passengers are dead, but Boeing's order book is still full.
Insurances rationally calculate a fatality in aircraft accidents somewhere between 2 to 4 million US $ per victim.
So we stay at about 1 billion US $ for lost lives. Plus another 1-2 billion payments to customers for lost revenue due to the grounding.
Versus 600 billion US $ for Boeing's backlog for the 737 MAX?
Of course there are also highly unpredictable non tangible risks in that equation, image related, fear of traveling public etc.
Probably manageable though, and overall, the cost analysis is still in favour of the hasty design and pseudo-certification procedure. And looking at the numbers, Boeing management still deserves their yearly bonus, no?

(if you find cynicism, you can keep it.)

Although it may well turn out to be the case, it is still an assumption that a malfunctioning AoA vane induced MCAS-trim-response is involved in both incidents.

The Lion incident in particular is intriguing in terms of three things:

1. the Captain repeatedly and successfully counteracting MCAS nose-down commands with electric trim but failing to activate the STAB TRIM CUTOUT.
2. the Captain transferring control to the F/O while just barely managing to keep the aircraft in "level" flight himself.
3. the apparently calm interactions of the crew with ATC.

This contrasts with what appears to have been the panicked response of the crew to the emergency encountered on ET602. It would appear that the two situations were quite different, or at least manifested in a significantly different way, or less likely (hopefully), the crew was not adequately briefed on how to correctly respond to a malfunctioning AoA vane induced MCAS-trim-response.

When it comes to safety, never allow the manufacturer to set and mark its own exams!

But I think the Lion Air flight had a bit more altitude to play with when the problem manifested itself, hence less panic??

Yeh. Think I made that point earlier based on such a blatantly naive solution to an Alpha ~ Stick force condition, messing so brutally with stab trim.

Literally, we seem to have a black and white MANDATORY CERTIFICATION requirement, ignored or overlooked by the project engineers who postulated moving these large engines up and forwards, developing into a mad rush for an affordable workaround... to a situation that would RARELY be met; would be UNDERSTANDABLE to a crew if it was; and which could ARGUABLY have been answered by a pre-existing and time-honoured stick shaker (or re-engineered shaker/ pusher pair)

Yup. that's where Ive been coming from too Nomad, for as long as I've been aware of MCAS

IAS disagree is a probable caution when you have an AOA disagree.

Well true.
But it is obviously not happening in the worldwide fleet of NG and other 737 or failures would be too common to even think of using a single source of data.
So what in the chain of electronics from the vane to the ADIRUs and MCAS is different in the MAX - something has increased the AoA sensor failure rate.

There are at least two incidents involving B38M operated by SWA, and perhaps, one more related incident involving Sunwing Airlines.Incidents 1 & 2:Investigators are examining how Boeing heeded earlier warnings about flight-control-sensor failures similar to the one implicated in 737 MAX crash

During the three weeks before Lion Air Flight 610 plunged into waters off Indonesia, Southwest Airlines Co. replaced two malfunctioning flight-control sensors of the same type that has been publicly implicated in the crash, according to a summary of Southwest maintenance records reviewed by The Wall Street Journal.

Both U.S. maintenance issues involved a Boeing Co. 737 MAX 8, the same model that crashed last month in Indonesia. The sensors measure whether the jetliner is angled above or below level flight. Those sensors, or related hardware, needed repairs in the Southwest instances, according to the summary document. The document also indicates Southwest pilots reported they couldn't engage automated throttle settings, similar to cruise control on a car.

A Southwest spokeswoman said the sensors didn't fail and were removed as a precautionary measure as part of a troubleshooting process. She said at least one was repaired...
[note: similarity to what had been reported anonymously on NASA's ASRS database.]


Incident 3 :Canadian investigators have disclosed that engineers replaced an air data computer on a Sunwing Airlines Boeing 737 Max 8 after the crew received spurious indications from the aircraft's instruments. Transportation Safety Board of Canada says the aircraft had been cruising at 35,000ft when the crew received "erroneous" indications on the captain's side. The first officer's instruments, and the standby indicators, were functioning normally and the first officer took control of the aircraft.

It descended to 25,000ft as a precaution, in order to clear instrument meteorological conditions, but "as it passed 28,000ft" the weather radar and TCAS both failed. The aircraft was some 50nm north-west of Washington DC at the time. The crew transmitted a "pan pan" urgency call. The safety board says a left-side inertial reference system fault light also illuminated. he flight continued to Toronto for a safe landing without further incident.

The Canadian TSB reported the left ADIRU was replaced before the plane returned to operation.

HI Folks Its Yanrair here again. Just for info. I have flown the B737 several variants over twenty + years, and, have flown it in Manual Reversion with only a 24 v battery powering the plane. IT IS A MECHANICAL AIRCRAFT WITH COMPUTERISED OVERLAYS AND IT FLIES WITHOUT THEM. Actually very well.
The pilot is connected to the main controls directly with a wonderful thing called Fly By Wire - stainless steel wire 12mm thick! Not an amp or a volt in sight.
It is the only modern aircraft that can still do this. And that is one of its greatest strengths the in my view.
I flew many times as a certified flight tester on the 737 on behalf of XXX. Now, the point being missed here in hundreds of posts is that it is focusing on technical issues to do with MACS. And is becoming terribly geeky and academic about flight control laws and computers. It is nor focussing on the primary cause of why a crash was not avoided even given some technical issues. If you can fly a 737 with literally nothing working but a little 24 v battery - and the MAX is as far as I know no different, how come these two crashed? All you do on a 737, and not to be too technical - we used to say, if you utter the words 'what the f!!**! is it doing now?' ( ie Don't understand why plane is behaving the way it is and you don't like it) then turn off the autopilot, switch off the 'Jesus' switches (STAB TRIM) and fly manually straight and level until you have found out what is wrong.
OK, like Sully, I am a little older than some of the newer pilots, but perhaps this is where we should be looking? Not at a spurious input by a computer that could have been over-ridden. There is a massive attempt after every accident to muddy the waters so as to avoid legal issues and distribute the blame elsewhere. Which can be very sad if it doesn't get to the root cause.
In case you think that if it's not the plane, then it must be the pilots, that is not necessarily the case. A pilot is the end product of a massive training program and it is the quality of that training program that delivers the pilots.
Hope this helps to focus us a little more away from algorithms and more towards a possible cause - human factors.
Cheers - I enjoy this thread and am amazed at the in depth technical knowledge of many contributors.
It is just that most crashes, like the Everglades which was caused by poor airmanship and a faulty light bulb, are not that complicated.

I am in no way trying to defend Boeing here but pls don't mix up turnover and profit. The latter is somewhere between 6-10% of the former in real life and earned only over quite a number of years (bookkeeping tricks aside) where a lot can still happen.

As noted in the numerous reports filed by pilots on very similar incidents, they simply turned off the autopilot.

The inherent difference here is the use and dependence on the AP.
As noted by one pilot, he usually doesnt engage it on until FL10, when he did, the ac began to squawk. Simply turning it off returned the ac to normal.

Perhaps this is why there are not as many incidents in more congested airspace, the ac is actually being flown. There are very few RNAV DEP.

That is what I was talking about.
From a very low 'improbable' level of failure there is suddenly a significant failure rate. Something has changed between the NG and the Max, and that something needs attention.
That is on top of ensuring that crews are up to speed in dealing with the subsequent failures and cacophony of warnings.