Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

[Dave Therhino]

Originally Posted by Loose rivets

Again, one of the main bee-in-my-bonet's issues. Just what is the truth about that second (underfloor) column switch? I know, it's the third time I've shouted that question.

The column cutout switch operates just as it does on the 737NG, stopping opposite automatic trim movement if the column is more than a certain amount away from the neutral position, EXCEPT when the MCAS activation command occurs. MCAS activation causes temporary bypass of the column cutout switch via an added relay. This was necessary because the flight condition for which MCAS was the "solution" is a aft CG flaps up turn in which the crew is pulling the column far enough to approach a turning stall. In this condition, the unmodified column force characteristics did not meet the requirement in 14 CFR 25.203(a) to have increasing force required to generate increased pitch. MCAS was added to use a trim change to cause more column force to be needed to continue to pitch up in this condition.

[rubik101]

I posted in the other thread rethiopian aircraft down. This thread seems better suited to my point. So, I repeat; Pitch-power-speed is the go-to mantra for most of us who learned to fly with an AVGAS engine, a fixed pitch propeller in front of us and an instructor to our right. However, when the aircraft misbehaves in an unexpected fashion not mentioned in any QRH or training manual then the sense of disorientation, surprise, incredulity, inadequacy, anger, and frustration will swamp the brain and preclude all rational thought. Disengaging the auto-pilot, leveling the wings, looking for the horizon, and applying 75% of available power will still appear to the observer as a failed exercise and lead to further confusion etc, intensifying the cycle until utter hopelessness swamps the poor pilot. Imho, these two MAX 8 crashes were design faults and Boeing is squarely to blame for the failure to engage with owners regarding the subtle changes to the anti-stall system. I am glad I was not on board because even though we can all sit here and imagine that we would have done it differently, many of us might not.

[Stan Woolley]

am glad I was not on board because even though we can all sit here and imagine that we would have done it differently, many of us might not.

Well said rubik.

[ATC Watcher]

@ rubik :

However, when the aircraft misbehaves in an unexpected fashion not mentioned in any QRH or training manual then the sense of disorientation, surprise, incredulity, inadequacy, anger, and frustration will swamp the brain and preclude all rational thought.

Absolutely true. I had already mentioned something this a few times on the other thread as human factors are a big part of the cause of these 2 accidents . Some tend to forget that in AF447 , at least 2 of the 3 were highly experienced on the A330 and all 3 trained to good standards at the time . They made lots of errors yes, , but your sentence above fits part the sequence of events of that flight.

[GordonR_Cape]

Originally Posted by ATC Watcher

rubik101
Absolutely true. I had already mentioned something this a few times on the other thread as human factors are a big part of the cause of these 2 accidents . Some tend to forget that in AF447 , at least 2 of the 3 were highly experienced on the A330 and all 3 trained to good standards at the time . They made lots of errors yes, , but your sentence above fits part the sequence of events of that flight.

Just to clarify that we are on the same page about the role of human factors: My interpretation is that the pilots failed because they were imperfect, and the system failure set them up, so that several less than perfect choices led to a fatal outcome.

Somewhat off-topic, but I was reminded of this last week while watching an old-quiz show. The utter confusion in the minds of the contestants is obvious, and anyone who already knows the answer can't believe that they get the answer wrong. This inability to infer the complex mental state of another person frequently underlies these discussions, particularly the "just fly the aircraft" comments.

[Jetthrust]

Originally Posted by GordonR_Cape

Very lengthy and moderately detailed article just popped up on my newsfeed... Typical paragraph, relevant to this thread:

So had anyone checked, they might have flagged MCAS for one of several reasons, including its lack of redundancy, its unacceptably high risk of failure, or its significant increase in power to the point that it was no longer just a “hazardous failure” kind of system.

Great article. And, your quote goes to the heart what I think is a very significant question: is MCAS software now level A, given the proven consequences of its failure ? Given no one has (yet) answered, I am suspecting no one knows?

I wonder if Boeing are arguing that now it has 2 sensors, it’s failure is no longer catastrophic. But that would appear to be incorrect logic. It’s chance of failing is less, but the consequence of failing is still the same. Under the other argument, nothing would ever be classified as catastrophic, because anything in that category would be mitigated to a reduced level. Hence, nothing would be level A software, which is clearly not the case.

Takwis gives a great description of what happens when software isn’t as robust as it should be....

[WHBM]

Originally Posted by Smythe

Simple fix:

Increase the height of the landing gear (which should have been done 15 years ago) and put the damn motors back where they are supposed to be.

That $2 billion it was gonna cost looks pretty cheap right now...

Apart from all the other considerations, I understand that an increased height landing gear did not fit in the space available within the main structure, which meant that would have to be completely re-engineered. It goes right back to the "squashed" look of the Classic's engines, done to fit within the ground clearance because the gear leg length could not be increased.

[Jwscud]

I very much hope that somewhere in this procedure, ideally in one of the accident reports, but sadly more likely as part of the legal disclosures in the civil actions we see the underlying data.

There is a lot of good written info, and some informed speculation by those with far better engineering backgrounds and minds than mine, but what I think all of us want is the hard data in the form of the stick force/g graphs, the Cm/alpha graphs and the flight test reports that lead to the need for MCAS.

At at the moment we know that the aircraft has an aero problem that was uncertifiable, but not the areas of the envelope it affects or its severity which means we are missing a lot of the key context to evaluate what was going on at Boeing during the flight test campaign and certification.

[Takwis]

Originally Posted by Dave Therhino

The column cutout switch operates just as it does on the 737NG, stopping opposite automatic trim movement if the column is more than a certain amount away from the neutral position, EXCEPT when the MCAS activation command occurs.

...precisely when the column cutout switches are needed the most.

Originally Posted by Dave Therhino

MCAS activation causes temporary bypass of the column cutout switch via an added relay.

From my...limited...understanding of the wiring diagram, it uses the same relay as the STAB TRIM OVRD switch, being an easy back door into the trim system.

[thcrozier]

WSJ article today:
Boeing’s Own Test Pilots Lacked Key Details of 737 MAX Flight-Control System

[Dee Vee]

Originally Posted by thcrozier

WSJ article today:
Boeing’s Own Test Pilots Lacked Key Details of 737 MAX Flight-Control System

https://www.wsj.com/articles/boeings...em-11556877600

Anyone else gobsmacked with Boeings constant denial of the truth??

Boeing Co. limited the role of its own pilots in the final stages of developing the 737 MAX flight-control system implicated in two fatal crashes, departing from a longstanding practice of seeking their detailed input, people familiar with the matter said.

A Boeing spokesman said test pilots and senior pilots didn’t have less of a role in the design, briefing and testing of the final version of MCAS when compared with their counterparts who worked on previous models featuring important new systems.

[GordonR_Cape]

Originally Posted by Dee Vee

https://www.wsj.com/articles/boeings...em-11556877600

Anyone else gobsmacked with Boeings constant denial of the truth??

This saga is turning into a Nixon-Watergate situation: The coverup, obfuscation and denials are worse than the original "errors". The weekly drip-drip of new revelations, makes it even harder to restore credibility.

[Water pilot]

A Boeing spokesman said test pilots and senior pilots didn’t have less of a role in the design, briefing and testing of the final version of MCAS when compared with their counterparts who worked on previous models featuring important new systems.

Um, that statement does not exactly inspire confidence in their other models. I think they need a new spokesperson. When in hole, stop digging.

If the article is truly implying that the test leads did not have full specifications then that is so literally unbelievable that I don’t believe it. It is behind a paywall so I don’t know if it went that far. It does indicate that somebody at Boeing is not buying the party line that MCAS is perfect since they feel the need to deflect blame.

[Dee Vee]

Originally Posted by Water pilot

It is behind a paywall

https://i.imgur.com/tKmH1m7.jpg

[Smythe]

The WSJ is certainly taking on an investigative reporting role in this debacle....very interesting.

This seems to tell a different story that what I have heard before. That MCAS was originally designed to 0.6 degrees, and the test flights showed it needed 2.5 degrees. Now, this says the test pilots didnt know about the 2.5 degrees?

Originally Posted by Smythe
Simple fix:

Increase the height of the landing gear (which should have been done 15 years ago) and put the damn motors back where they are supposed to be.

That $2 billion it was gonna cost looks pretty cheap right now...

Apart from all the other considerations, I understand that an increased height landing gear did not fit in the space available within the main structure, which meant that would have to be completely re-engineered.

yes, re-engineering the wingbox, that was the $2 billion cost years ago...

Correction: For the MAX 8, the engines were move fwd/up to get same clearance as the 738 (so no mod to landing gear) For the MAX 10, they re-engineered the landing gear to a scissor to get some added height, (but still needed to move the engines fwd/up..I am unclear if the engine location on the 10)

You Tube

[Bend alot]

Originally Posted by Smythe

The WSJ is certainly taking on an investigative reporting role in this debacle....very interesting.

This seems to tell a different story that what I have heard before. That MCAS was originally designed to 0.6 degrees, and the test flights showed it needed 2.5 degrees. Now, this says the test pilots didnt know about the 2.5 degrees?




yes, re-engineering the wingbox, that was the $2 billion cost years ago...For the MAX, they re-engineered the landing gear to a scissor to get some added height, but still needed to move the engines fwd/up..
https://www.youtube.com/watch?v=F4IGl4OizM4

It reads as if it was never even tested to the limits, in any of the test flights.

[Smythe]

Yes, it does seem to read that way. I can understand why it is not decisively worded, as there are just so many test pilots in the program, and a definitive quote could easily be attributed...

The lazy B needs to get in a serious damage control mode, this is really getting out of hand.

[GordonR_Cape]

Originally Posted by Bend alot

It reads as if it was never even tested to the limits, in any of the test flights.

I think the emphasis on flight testing is slightly misplaced, for two reasons:
- The post crash simulator tests found that MCAS behaves as expected.
- Injecting faulty AOA data into a flight test is impractical.

However it seems to speak of a corporate culture, and the pressure to complete the launch. IMO the fault tree analysis could certainly have benefited from pilot inputs, or at least employees outside of the closed group responsible.

[safetypee]

Gordon,
‘The post crash simulator tests found that MCAS behaves as expected.’
A greater concern would be if the aircraft did not behave as expected in comparison with the FDR during the attempted recovery; then that would be more than impracticable to inject a false AoA signal during a flight test or fly any similar test !

[fred81]

Originally Posted by Smythe

The WSJ is certainly taking on an investigative reporting role in this debacle....very interesting.

This seems to tell a different story that what I have heard before. That MCAS was originally designed to 0.6 degrees, and the test flights showed it needed 2.5 degrees. Now, this says the test pilots didnt know about the 2.5 degrees?

Not necessarily. If it was demonstrated during test flights that with the original MCAS longitudinal stability criteria (i.e. required stick force) were not met, that would have been all the pilots knew at that time.

The subsequent authority increase to 2.5 degrees could have been kept from the test pilots. They would just demonstrate that the revised MCAS now meets the FAA requirements.