I doubt that was the trigger, BA have telegraphed for a while that they would have to suspend production if the grounding extended past the end of 2019.
I suspect it is due to "simple" (that is if you have an advanced accounting degree which I don't ) math balancing the cost of continued production against the cost of a shutdown/restart.
At some point the cost of cash to cover production/storage would start to go up significantly.

Other factor could be advanced payments that were due X months before scheduled delivery, I would guess (understatement here) that those have pretty much dried up.

The 737 Max fleet flew for a bit under 400,000 flight hours before the first accident, and the second occurred with the fleet at just under 800,000 hours. The demonstrated catastrophic accident rate at that point was about 1/400,000 per flight hour, or about 3x10E-6. This is roughly 100 times worse than the overall average transport airplane rate of catastrophic accidents due to all causes in the developed nations of Europe, North America, and Asia. This is about what you'd expect with non-fail-safe system design in just one truly critical system with dependence on typical electro-mechanical devices.

The rate of AOA sensor failure on the max was not unusual. If you monitor AOA sensor failures across a broader fleet, their average failure rate is consistent with the max experience. They occur for various reasons, and bird strikes are not the most common reason, but the average rate of failure is comparable. I've seen several reports on the NG over the past year for example.

The space shuttle's operating environment was very different and its mission was inherently high risk. Its average rate of a catastrophic event during launch and re-entry was about 1/100 per flight hour even with excellent systems designs due to the need for minimum weight and the operating conditions of orbital speeds and transition from and to flight in the atmosphere. Its relevance to the max issues is limited other than to show what first-class critical flight control systems design looks like.

Dave Therhino

Shuttle - I think you mean per flight. Back when I worked the figure was 1/100 per flight.
I think the real concern is that Boeing programmed their flight software - MCAS
to rely on a potentially unreliable sensor. MCAS was not able (programmed) to detect
the failing sensor. Perhaps MCAS should have had a sanity check on reported AOA.
How one validates such an apparently Ad-hoc piece of software is beyond me.

My previous comment should have indicated that the expectation of an event is in the numbers
that you (NASA or Boeing or FAA) should be calculating with.

How about leaving MCAS the way it was and just change the AoA-sensors to some failsafe (including wrong installation and birdstrike) system? Like LIDAR or similar?

Maybe not since 1952 and we all know what happened to:
de Havilland DH 106 Comet

I agree the number is also a good approximation of the per cycle risk because launch and re-entry were by far the most risky phases of flight. There were something like 150 missions (it's been a while since I added them up for a study), and two accidents, one on launch and one on re-entry. I specifically gave a ballpark per hour rate for launch and re-entry, for which I guessed 1 hour of exposure per cycle to those phases of flight. The risk in orbit is much lower, but still quite high theoretically compared to a commercial flight, though the record was good for those 150 or so flights.

I'm not sure I'm grasping everything you were trying to say with the rest of your comment, but my point was the AOA sensor behavior in the max fleet was not a huge outlier failure-rate wise, and it was the system architecture that caused the problem. I think we are probably saying the same thing.

The sensors can always fail, even multiple sensors will fail in the same way sometimes (icing.) You have to make sure that when they fail, the plane degrades gracefully and predictably rather than pointing its nose at the ground. I seem to remember that some European guys were working on such a concept, whatever happened to it?

It occurs to me that all of the solutions that Boeing is now proposing (to a problem that they still have trouble admitting exists) were solutions that had to have been considered and discarded during the initial design of the MAX. They have proposed nothing that would have incurred any significant cost to the program, so why is this new way better? We are now trading out false activation of MCAS for false deactivation, and if MCAS was so important that it was worth the 346 lives lost why are we so casually disabling it? Remember that Boeing told the American President that the plane was perfectly safe after the second accident.

Actually no.
The Comet 1 was in airline service for just under two years before grounding, the same as the MAX.

In that time it killed 110 souls, compared with the MAX's 346.

Much smaller aircraft, of course.

The article you linked to states that Boeing expects to not pursue stock buybacks for the next several years.

In fact, Boeing previously announced that they had stopped buybacks in mid-March, during the Q1 2019 earnings call on 24 April 2019. Transcript: https://s2.q4cdn.com/661678649/files/doc_financials/quarterly/2019/q1/1Q19-Earnings-Call-Transcript-(1).pdf

Reviewing the 1Q, 2Q, and 3Q quarterly reports confirms this. $2341M worth of common shares were repurchased in Q1, $310M repurchased Q2 (with a note in the quarterly report that these were contractually obligated) and $zero repurchased Q3. Want to wager on what Q4 will say?

https://investors.boeing.com/investo...s/default.aspx

Wonder if they kept the -800 and -900 jigs? Just start building those again.

The 757 was cancelled because it received zero orders in 2002, 7 orders in 2003, zero orders in 2004, and zero orders in 2005. It's not a conspiracy, it costs a fortune to maintain capital equipment and real estate to support a product that is not generating revenue.

Many would point to the merger with McDonnell-Douglas in 1997 as the point where Boeing's culture and direction shifted. The relocation of the headquarters to Chicago directly traceable to that event. Boeing's troubles could be traced to McDonnell Douglas purchase - LA Biz Observed

Of course, the failure of today's Boeing 'Starliner' launch just increases confidence.

I heard there was something wrong in the programming of rocket burn ....

Both accidents were on launch. The final destruction of the second shuttle was delayed until re-entry, but Shuttle Columbia was fatally damaged during its launch for very similar reasons to the fatal damage of Shuttle Challenger; an acceptance of repeated damage due to previously noted defects in the design and a willingness to continue with them unresolved.

I think the launch event, from engine ignition to orbit is about 8-1/2 minutes, with the boosters running slightly more than 2 minutes. https://www.nasa.gov/mission_pages/s...-leinbach.html

They aren't fuel efficient enough.

Rocket ignition timing relying on a single clock. Which failed...

Not enough info released yet to say for sure, could also have been a mistake in a timing driven script that had an incorrect value, in hotel layover terms : clock correct, wrong alarm time set.
Either way not a good day for Boeing.

I almost missed a flight once due to the classic AM/PM mistake, always use 2 alarms for anything critical since then.

Now back to our regularly scheduled "not rocket science" 737/MAX programming.

The $ 20 Timex took a multi G licking- but didn't keep ticking.

But look at the $$ saved and schedule met

Doing so well that it won't rendezvous with the ISS and will be returning early. Sounds like NASA officials are taking over the role of the Boeing smoke and mirrors department.

Actually yes... if you go back and research DC6 or Lockheed Constellation or even DC3s, there were many accidents each year that added up to that number of fatalities and much more! Many of the accidents were no due to the aircraft itself. Even the B707 and DC8 had more annual fatalities.

Certainly bad luck for those who died due to poor design at best or an apparent careless concern for real safety over profit more than likely