gia777 wrote:

There should be adaptive cruise control system like in your car where you cannot hit the car in front of you and the plane should have this as well to prevent hitting a sea or mountain should the plane on course of collision. The system can kick in and take over the control automatically. the system can be manually on and off.

While that "cruise control system" is, in itself, a good idea, it must rely on correct data in order not to endanger the plane further. For example, g load limits, airspeed limits....... and AoA.


David

A 737 pilot has made comments on the Lion Air incident here.

https://youtu.be/6TXfkAHR_6Q?t=152

He mentions that the auto trim can potentially trim to such a position that the elevator would not have enough leverage to pull the plane back up, even if the pilot was fully pulling back on the yoke.

His point is, if the flight crew was in the middle of running checklisk/memory-items for the flight instrument disagree issue and suddenly the auto-trim fires up, they only have moments to react and recover seeing as they are on low altitude.

He also makes a point that no one will know for sure what the flight crew was facing until the CVR is found.

benjjk wrote:

So MCAS - let's not forget that it is a good system, when working properly. And the FAA definitely knew about it because it was required to meet the regulatory requirements I referred to.

So if the FAA knew about MCAS why did neither AAL nor SWA know about it? MCAS is not listed in the Difference Tables in the FAA's Flight Standardization Board Report nor is it listed in the Transport Canada report. It is, however, listed in the Difference Tables in the Brazilian Agência Nacional de Aviação's Operational Evaluation Report. All of which are a quick google away for those interested. The Brazilian evaluation was finalized this year, the American and Canadian evaluations last year.

IADCA wrote:

dakota123 wrote:

runway23 wrote:

Were either aircraft types that crashed recently put (rushed) into service ? Answer is no. 737Max was rushed through certification on the premise that everything was similar to 737NGs, yet Boeing made significant changes and failed to advise its customers. Such changes should have been discovered by the FAA during certification.

.

You SURE you want to start down that road? https://en.m.wikipedia.org/wiki/Lufthansa_Flight_2904

From the perspective of an objective observer, your response appears to serve no purpose other than trying to start a game of Airbus-Boeing whataboutism. The incident you referenced isn't remotely comparable: it happened on an aircraft type that had already been in service for several years and wasn't a grandfathered derivative of another type. It's almost a total non sequitur, in fact.

You’re kidding, right? Re-read the dude’s patently inflammatory statements, in this thread and others.

Argue all you want that the type had been in service for a few years. It’s irrelevant. Fact is, a set of circumstances arose that Airbus hadn’t anticipated, and one can argue that the issue that arose was pretty obvious in hind site. One can further imagine that Airbus hadn’t briefed that in a crosswind landing it would take 6 tons (or whatever) on both mains before braking could begin, and maybe on a rain-slick runway with a tailwind component one shouldn’t attempt it. And it was a NEW type. So by your logic, it should have been perfect and not contain any logic flaws whatsoever.

Simple point is that issues happen from time to time that a manufacturer of complex machinery, for whatever reason, don’t anticipate (and we don’t even know what happened here.)

Please stop the vilification bulls**t. None of these people (Airbus or Boeing Or Bombardier or whomever) are evil.

PixelFlight wrote:

But the way actual civil aircraft are designed rely on old architecture where the data from all the sensors are keep isolated at the system level, and rely on arbitration to reject failed sensor. A new architecture must be used to take account of every single information available to do data fusion, increasing precision and reliability. So the automation could have been keep enabled even with a failed sensor, avoiding the MCAS erratic action, and maybe automatically avoiding terrain once the autopilot will have the capability to do so. AFAIK Airbus TCAS is able to automatically avoid traffic at least on some aircraft model.

Maybe.

But I think there are different architecture options that one could pursue. The sensor fusion approach is a more integrated, more focused on getting the right output.

But another approach might be to make it easier and more detectable when things go wrong, and let the pilots fly the plane. This has been the philosophy in fact, but it seems it may have failed in the case of the MAX trim system (at least in terms of education, if not actual functionality).

Lets also remember that we do not know the sensors were the problem. In fact, since their repeated replacement work did not seem to fix the situation, it may not be the sensors but rather the computers reading them... we really don't know. An integrated system would also be subject to failures in the similar fashion.

zippy wrote:

So if the FAA knew about MCAS why did neither AAL nor SWA know about it? MCAS is not listed in the Difference Tables in the FAA's Flight Standardization Board Report nor is it listed in the Transport Canada report..

VS11 wrote:

"Southwest, American pilots unions question 737 Max documentation after Indonesia crash"

"Two U.S. pilots' unions say the potential risks of a safety feature on Boeing Co.'s 737 Max aircraft that has been linked to a deadly crash in Indonesia weren't sufficiently spelled out in their manuals or training....
....
Bnone of the documentation for the Max aircraft included an explanation of the system, the union leaders said.

A coworker recently toured SWA's giant bank of state of the art 737NG simulators. They asked where the 737MAX simulators were and were told did not have/need any.

They reported back to me that SWA has some nice 737MAX advertisements/POSTERS on the wall though...

dakota123 wrote:

None of these people (Airbus or Boeing Or Bombardier or whomever) are evil.

That depends on what you define as evil and if it is the same all across.

AirlineCritic wrote:

But I think there are different architecture options that one could pursue. The sensor fusion approach is a more integrated, more focused on getting the right output.

But another approach might be to make it easier and more detectable when things go wrong, and let the pilots fly the plane. This has been the philosophy in fact, but it seems it may have failed in the case of the MAX trim system (at least in terms of education, if not actual functionality).

The two approaches are not required to be exclusive. The "detect and disable" approach can still be used in case the pilot don't like the "sensors fusion" approach. More care must be done to avoid sudden automation disconnection when just a sensor fail while the required air data can still be reliably computed in a other way.

AirlineCritic wrote:

Lets also remember that we do not know the sensors were the problem. In fact, since their repeated replacement work did not seem to fix the situation, it may not be the sensors but rather the computers reading them... we really don't know. An integrated system would also be subject to failures in the similar fashion.

While it's true that we don't yet know for this case if it's the sensor itself or some connector, wires, or the computer that produce erratic values, the architecture isolating signals make the whole system fragile. Architectures that connect nodes in serial are less reliable than architectures than connect nodes in parallel.

U.S. FAA launches high-priority probe of Boeing's safety analyses -WSJ

Well the good news is that this particular issue will be addressed and hopefully make the max a safer plane. But as always, it's at the expense of a major loss of life. The question is, what other issues are potentially unknown.

PixelFlight wrote:

... More care must be done to avoid sudden automation disconnection when just a sensor fail while the required air data can still be reliably computed in a other way.
....

are you sure?

initial climbphase
the system knows (or could easily know) the attitude by the gyro
the system knows (or could easily know) the groundspeed by GPS
the system knows (or could easily know) the acceleration or decceleration by gyro
the system knows (or could easily know) the approximate climb- or sinkrate by GPS


now some - as unreliable known - outboard sensor transmitts erroneous data

solution 1:
to avoid sudden automation disconnecion the system nosesdives the plane into the ground

solution 2:
to system judges that the inboard sources from gyro an GPS are more trustful than the outboard sensor
but the system does not know the airspeed and can no longer automate the flight
so the system
2a.) disconnects and hands over the plane to the pilotes withaout any intervention in attitude so pilots can handfly the plane alonge and try to troubleshoot
2b.) the system calculates a appropiate pitch&power setting for the actual load, speed and height, sets that values and hands over the plane to the pilots in that stabile attitude

i`m not sure if i would deside 2a or 2b

but you would really deside 1.) ?

dakota123 wrote:

IADCA wrote:

dakota123 wrote:

.

You SURE you want to start down that road? https://en.m.wikipedia.org/wiki/Lufthansa_Flight_2904

From the perspective of an objective observer, your response appears to serve no purpose other than trying to start a game of Airbus-Boeing whataboutism. The incident you referenced isn't remotely comparable: it happened on an aircraft type that had already been in service for several years and wasn't a grandfathered derivative of another type. It's almost a total non sequitur, in fact.

You’re kidding, right? Re-read the dude’s patently inflammatory statements, in this thread and others.

Argue all you want that the type had been in service for a few years. It’s irrelevant. Fact is, a set of circumstances arose that Airbus hadn’t anticipated, and one can argue that the issue that arose was pretty obvious in hind site. One can further imagine that Airbus hadn’t briefed that in a crosswind landing it would take 6 tons (or whatever) on both mains before braking could begin, and maybe on a rain-slick runway with a tailwind component one shouldn’t attempt it. And it was a NEW type. So by your logic, it should have been perfect and not contain any logic flaws whatsoever.

Simple point is that issues happen from time to time that a manufacturer of complex machinery, for whatever reason, don’t anticipate (and we don’t even know what happened here.)

Please stop the vilification bulls**t. None of these people (Airbus or Boeing Or Bombardier or whomever) are evil.

The point is that what you said doesn't respond to what he said. Your points are correct, they're just non sequiturs. He's talking about something being rushed into service, and you're talking about a different topic. That street does go both ways, of course, but it is one reason many of these threads devolve.

asdf wrote:

now some - as unreliable known - outboard sensor transmitts erroneous data

solution 1:
to avoid sudden automation disconnecion the system nosesdives the plane into the ground

solution 2:
to system judges that the inboard sources from gyro an GPS are more trustful than the outboard sensor
but the system does not know the airspeed and can no longer automate the flight

solution 3:
The system use predictor algorithms with data from all sources to compute the most accurate airspeed as possible (sensors fusion). It inform the pilot that the airspeed is possibly less accurate due to a sensor error and let's the pilot decide, by monitoring the flight, if it still let the automation on or if it take the control manually.

The current problem with actual design is that air data are discontinuous, either valid or invalid with sharp transition. There exists algorithms to make air data continuous, less prone to go in the invalid region, and if so in a slow move.

PixelFlight wrote:

U.S. FAA launches high-priority probe of Boeing's safety analyses -WSJ

Do you have a link for this article?

PixelFlight wrote:

U.S. FAA launches high-priority probe of Boeing's safety analyses -WSJ

Apparently not.

https://uk.reuters.com/article/uk-boein ... KKCN1NJ09U

(Reuters) - The U.S. aviation regulator denied on Tuesday a report that it had launched a new probe of the safety analyses performed over the years by Boeing Co (BA.N) on its 737 MAX models, following the crash of a Lion Air jet in Indonesia last month.

Questions....

There is mention in some articles about a needed software upgrade to the MCAS system:

- How long might this take to accomplish and then to implement?

- What might this look like? Is it as simple as shutting down MCAS when you have unreliable AoA or when the pilots pull up on the yoke?

scbriml wrote:

PixelFlight wrote:

U.S. FAA launches high-priority probe of Boeing's safety analyses -WSJ

Apparently not.

https://uk.reuters.com/article/uk-boein ... KKCN1NJ09U

(Reuters) - The U.S. aviation regulator denied on Tuesday a report that it had launched a new probe of the safety analyses performed over the years by Boeing Co (BA.N) on its 737 MAX models, following the crash of a Lion Air jet in Indonesia last month.

Time will tell what's really going on. From the basic fact that the accident occurred, there is no way that the safety activity is not reviewed to some extend. I suspect that the scale of this activity is the subject of this PR war.

Update: the WSJ have changed the title of there article since: https://www.wsj.com/articles/faa-launch ... 1542154515 but "high-priority review of the safety analyses" is still on the beginning of the text at this time.

djm18 wrote:

Questions....
- What might this look like? Is it as simple as shutting down MCAS when you have unreliable AoA or when the pilots pull up on the yoke?

Given that the pilots were never informed about MCAS, and given that the transition course from the NG to MAX models just takes an hour, it's impossible that Boeing offered a possibility to shut down MCAS. In fact, the MAX was advertised as a plan that can be operated like the NG - which does not have MCAS.

As Aragorn says, one does not simply shut down MCAS. It degrades flight characteristics in a way that introduces other risks. First, FAA and Boeing need to evaluate all involved risks. They need to develop an algorithm which allows pilots to reliably detect an MCAS failure.


David

WIederling wrote:

dakota123 wrote:

None of these people (Airbus or Boeing Or Bombardier or whomever) are evil.

That depends on what you define as evil and if it is the same all across.

Thanks to remarks like this, this thread is uncomfortable to read. You and a few others have seized on it as an opportunity to promote some sort of partisan agenda, now most clearly expressed by your implication that Boeing are evil. What motivates you to make these comments, and why is it so important to you that Boeing be at fault? There are about three of you who are almost cheering for that result.

flyingturtle wrote:

djm18 wrote:

Questions....
- What might this look like? Is it as simple as shutting down MCAS when you have unreliable AoA or when the pilots pull up on the yoke?

Given that the pilots were never informed about MCAS, and given that the transition course from the NG to MAX models just takes an hour, it's impossible that Boeing offered a possibility to shut down MCAS. In fact, the MAX was advertised as a plan that can be operated like the NG - which does not have MCAS.

As Aragorn says, one does not simply shut down MCAS. It degrades flight characteristics in a way that introduces other risks. First, FAA and Boeing need to evaluate all involved risks. They need to develop an algorithm which allows pilots to reliably detect an MCAS failure.


David

Agree

And if they don't want to introduce Max specific high AOA handling training, only detecting and announcing MCAS failure is not enough. MCAS and AOA probes can be in failed state when aircraft is high AOA and approaching stall. In that case of MCAS unavailable, pilot would need to do the job of MCAS

Maybe if they spent as much time and effort on updating pilots on what they might face flying the plane, as they did trying to bullshit the public about how competitive it is, they might have found it worthwhile to include info on the MCAS in the manuals.

flyingturtle wrote:

djm18 wrote:

Questions....
- What might this look like? Is it as simple as shutting down MCAS when you have unreliable AoA or when the pilots pull up on the yoke?

Given that the pilots were never informed about MCAS, and given that the transition course from the NG to MAX models just takes an hour, it's impossible that Boeing offered a possibility to shut down MCAS. In fact, the MAX was advertised as a plan that can be operated like the NG - which does not have MCAS.

As Aragorn says, one does not simply shut down MCAS. It degrades flight characteristics in a way that introduces other risks. First, FAA and Boeing need to evaluate all involved risks. They need to develop an algorithm which allows pilots to reliably detect an MCAS failure.

David

If they need MCAS to safely fly, they are in trouble.

caoimhin wrote:

WIederling wrote:

dakota123 wrote:

None of these people (Airbus or Boeing Or Bombardier or whomever) are evil.

That depends on what you define as evil and if it is the same all across.

Thanks to remarks like this, this thread is uncomfortable to read. You and a few others have seized on it as an opportunity to promote some sort of partisan agenda, now most clearly expressed by your implication that Boeing are evil. What motivates you to make these comments, and why is it so important to you that Boeing be at fault? There are about three of you who are almost cheering for that result.

Mostly the posters that were so busy implicating the crew as nothing better than monkeys at the wheel, "RTFM", "no professional US pilot would have made the same error" excluding all possibility of Boeing having made an error here. And in a pretty aggressive tone at that.
nobody mentioned monkeys varbatim but ... .
No surprise posters that are so partisan polarizing find reflection of their style even more unacceptably polarizing .. while in no way retreating from their own position.

WIederling wrote:

"RTFM"

Bjorn has a write up on the MCAS system on leehamnews. It seems that the procedure to deal with a runaway trim in this instance is not exactly the same as what's been spelled out before. The MCAS trim doesn't stop when the yoke is pulled back, which as he rightly points out, would be counter-intuitive to its purpose.

Aren't they jumping the gun a bit by making all these claims before we have the CVR?

My biggest question in all of this... On the doomed flight and the flight previous, the pilots made indications that they wished to return to their origin. Why did they not return? I understand this is something we likely won’t know until CVR is recovered.

rj777 wrote:

Aren't they jumping the gun a bit by making all these claims before we have the CVR?

We already know the situation is bad. The CVR will tell us how much worse it was. How the crew dealt with a system which suddenly emerged out of the dark...



Investigators: "Here, we have a 737 instructor. You have trained him in Seattle. He says the aircraft behaved in a way which shouldn't happen."

Boeing: "Oh."

Investigators: "Does the 737MAX control logic differ in any way from the 737NG?"

Boeing: "Errrrmmmm......"


David

rj777 wrote:

Aren't they jumping the gun a bit by making all these claims before we have the CVR?

One thing is pretty clear: a certain system was implemented, not described to the crew (and possibly to certification authorities). Characteristics of a system are such that it can contribute to the crash, effectively overruling pilot's control, in non-standard flying conditions.
It is not jumping the gun, this is a problem. Technical, legal and PR. And questions about other non-disclosed changes to MAX are definitely going to be asked. And someone in Chicago may have hard time answering those.

rj777 wrote:

Aren't they jumping the gun a bit by making all these claims before we have the CVR?

Yes. But it's not surprising given the manufacturer. The CVR will probably tell us whether it's the 2nd or 3rd most important factor in this crash. I don't find it surprising that #1 and the potential #2 are being ignored now.

I sure don't want to fly on any 737 MAX8s until this issue is fully resolved!

Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

1 Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control aircraft pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged.
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer
trim wheel . . . . . . . . . . Grasp and hold
6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
7 Anticipate trim requirements.
- - - - - - - - - - - - - -

That procedure WILL stop MCAS or any trim from operating the trim motor. MCAS is also described in my MAX maintenance training manuals.

MSPNWA wrote:

rj777 wrote:

Aren't they jumping the gun a bit by making all these claims before we have the CVR?

Yes. But it's not surprising given the manufacturer. The CVR will probably tell us whether it's the 2nd or 3rd most important factor in this crash. I don't find it surprising that #1 and the potential #2 are being ignored now.

it may be 10th contributing factor. Wouldn't affect FAA actions, though, as Boeing is caught red handed.

All manufacturers do the same thing. Up until USAir ditched in the Hudson there was envelope protection information that AB wasn't providing to the flight crews. Sullenberger had very little if any pitch control for the final 150ft and basically none for the last 50ft -- very disconcerting for a pilot but everybody go out ok. AB got a slap on the hand and after that it was recommended they be more forthcoming with information about their protection modes.

7BOEING7 wrote:

All manufacturers do the same thing. Up until USAir ditched in the Hudson there was envelope protection information that AB wasn't providing to the flight crews. Sullenberger had very little if any pitch control for the final 150ft and basically none for the last 50ft -- very disconcerting for a pilot but everybody go out ok. AB got a slap on the hand and after that it was recommended they be more forthcoming with information about their protection modes.

Yep, in car world - Volksvagen also did something similar...

[quote="fadecfault"]Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

1 Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control aircraft pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged.
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer
trim wheel . . . . . . . . . . Grasp and hold
6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
7 Anticipate trim requirements.
- - - - - - - - - - - - - -

Almost exactly the same as the NG checklist I have but it's a little old -- doesn't include the autothrottle disengage step.

MSPNWA wrote:

I don't find it surprising that #1 and the potential #2 are being ignored now.

That is because the ranking of factors at this point is highly subjective. Your #1 and #2 seems not to be so relevant for most other posters.

fadecfault wrote:

Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

1 Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control aircraft pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged.
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer
trim wheel . . . . . . . . . . Grasp and hold
6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
7 Anticipate trim requirements.
- - - - - - - - - - - - - -

That procedure WILL stop MCAS or any trim from operating the trim motor. MCAS is also described in my MAX maintenance training manuals.

I was wondering about that. Thank you for posting.

SurlyBonds wrote:

I sure don't want to fly on any 737 MAX8s until this issue is fully resolved!

Thanks for sharing!!!

rheinwaldner wrote:

That is because the ranking of factors at this point is highly subjective. Your #1 and #2 seems not to be so relevant for most other posters.

That begs the question of why they're not as relevant.

MSPNWA wrote:

rheinwaldner wrote:

That is because the ranking of factors at this point is highly subjective. Your #1 and #2 seems not to be so relevant for most other posters.

That begs the question of why they're not as relevant.

Because those factors may be one of a kind situations. Trim control system and related topics frame dynamic performance are type specific and concern each and every MAX frame.

Think about it in such a way - someone is brought to doctor due to a cracked rib. But x-ray also showed a dark spot in the lung. While broken rib may be the one which causes pain, guess where doctors will be looking most....

MSPNWA wrote:

rheinwaldner wrote:

That is because the ranking of factors at this point is highly subjective. Your #1 and #2 seems not to be so relevant for most other posters.

That begs the question of why they're not as relevant.

Because they would rank them maybe as #5 or #9 (equally subjective as you ranked them)?

rheinwaldner wrote:

Because they would rank them maybe as #5 or #9 (equally subjective as you ranked them)?

Which is quite illogical as without a plane flying with an AoA sensor issue, we don't have a crash. Instead one factor that may have contributed to the lack of a safe recovery is the focus.

But I know why. And it's disturbing.

I would be very interested to know how difficult it really is to override the automatic stall protection. Is it even possible under the circumstances of the accident flight?

benjjk wrote:

LDRA wrote:

VS11 wrote:

"Southwest, American pilots unions question 737 Max documentation after Indonesia crash"

"Two U.S. pilots' unions say the potential risks of a safety feature on Boeing Co.'s 737 Max aircraft that has been linked to a deadly crash in Indonesia weren't sufficiently spelled out in their manuals or training.

Boeing and the Federal Aviation Administration issued directives last week telling flight crews about the system, which is designed to provide extra protection against pilots losing control. That prompted aviators, unions and training departments to realize that none of the documentation for the Max aircraft included an explanation of the system, the union leaders said."

https://www.dallasnews.com/business/air ... esia-crash

Damning...

Is this MCAS added in order to maintain same flight characteristics as older 737NG?

As I understand it, the MCAS was added to assist with stall prevention/recovery, because the Max is harder to recover due to the forward CG. It only operates in manual, flaps-up flight at high angle of attack. A certification requirement would have been for the Max to have virtually identical flight characteristics to the NGs which in normal flight it does (I assume), but not at high AoA. Happy to be corrected on any of this by someone with some actual 737 experience.

Probably not a great move to not even mention the system once in the training packs, given how it is a shift away from the perceived Boeing philosophy of the pilot having the final say in what happens. Whether pilot awareness of it would have saved this flight we can't say though. I can't see how the MCAS by itself could bring down the aircraft if it can be so easily corrected by pulling back on the yoke and applying some trim, or the usual trim runaway procedure. Something else was going badly wrong in that cockpit.

What drove requirement to add MCAS is currently the billion dollar question.

If it is only driven from requirement to maintain same flight characteristic as 737NG, then it is less severe. Boeing can get away with a Max high AOA handling difference course.

If it is actual driven from the need to meet stall characteristic clauses(i.e. 25.203) in Part 25, then there will be deep trouble for Boeing.

MCAS would fail every.single.clause in Part 25 Section 25.672 Stability augmentation and automatic and power-operated systems:

If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with §25.671 and the following:

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in §25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system—

(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

(2) The controllability and maneuverability requirements of this part are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and airplane configurations) which is described in the Airplane Flight Manual; and

(3) The trim, stability, and stall characteristics are not impaired below a level needed to permit continued safe flight and landing.

https://www.ecfr.gov/cgi-bin/text-idx?S ... 2&rgn=div8

kalvado wrote:

7BOEING7 wrote:

All manufacturers do the same thing. Up until USAir ditched in the Hudson there was envelope protection information that AB wasn't providing to the flight crews. Sullenberger had very little if any pitch control for the final 150ft and basically none for the last 50ft -- very disconcerting for a pilot but everybody go out ok. AB got a slap on the hand and after that it was recommended they be more forthcoming with information about their protection modes.

Yep, in car world - Volksvagen also did something similar...

Volkswagen intended to defraud..

LDRA wrote:

What drove requirement to add MCAS is currently the billion dollar question.

Per Leeham, https://leehamnews.com/2018/11/14/boein ... he-pilots/

But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.

As far as I understand, stability at higher AOA is an issue to be mitigated by MCAS

LDRA wrote:

What drove requirement to add MCAS is currently the billion dollar question.

If it is only driven from requirement to maintain same flight characteristic as 737NG, then it is less severe. Boeing can get away with a Max high AOA handling difference course.

If it is actual driven from the need to meet stall characteristic clauses(i.e. 25.203) in Part 25, then there will be deep trouble for Boeing.

MCAS would fail every.single.clause in Part 25 Section 25.672 Stability augmentation and automatic and power-operated systems:

If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with §25.671 and the following:

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in §25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system—

(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

(2) The controllability and maneuverability requirements of this part are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and airplane configurations) which is described in the Airplane Flight Manual; and

(3) The trim, stability, and stall characteristics are not impaired below a level needed to permit continued safe flight and landing.

https://www.ecfr.gov/cgi-bin/text-idx?S ... 2&rgn=div8

Thanks for posting this. According to the Leeham article, the larger engines, further ahead of the CG than before, also produce a pitch up moment. This moment is amplified at a high AoA. So at a high angle on the precipice of a stall, where a classically stable aircraft would want to drop the nose the Max does the opposite (or at least, the pitch down force is not as prominent as an NG). It goes without saying that this is a very undesirable stall characteristic. So in my layman's opinion, MCAS would absolutely be considered a stability augmentation system.

If so the FAA must have ticked off on the 25.672 requirements, and I cannot think of how they got around point (a), especially because the pilots didn't even know the system existed.

I have appreciated the great, in-depth debate here on the systems. I'm not a pilot - instead an aviation enthusiast and auto mechanic. But I do like to sometimes try to contribute an outside-the--box, layman's-type view.

One issue that I don't see being discussed much at all on this thread, and which, to me, seems to make the situation more dangerous, is the fact that the problem happened to Lion Air not long after takeoff, with not a lot of altitude to play with for diagnosis and recovery.

Taking off out of LAX my whole life, I have always had in the back of my mind that the time of maximum hazard is when you're clearing the coastline and climbing out over Santa Monica Bay .... that if something happens to the engines/electrical system right then, there's not a lot of momentum or altitude to use to save the aircraft.

So what makes me concerned about this 737MAX issue is that - until the pilots fully identify and contain the problem, should it occur - the penalty could be a repeated (every 10 seconds?) loss of attitude and altitude through runaway trim. Upon takeoff, this can be the difference between recovery and tragedy.

When Pan Am 759 went down on takeoff due to a microburst in New Orleans in 1982,
https://en.wikipedia.org/wiki/Pan_Am_Flight_759

the final report found that the reaction time of the PF copilot, was almost enough to save the aircraft, but instead the 727 clipped the trees on the east side of Williams Ave. The report found that microburst training was not thorough enough at the time, and that the copilot did react reasonably quickly, but not quite quickly enough.

What makes me uncomfortable, as a passenger, is that the recognition time is one factor - but then if the aircraft repeats the bad maneuver every 10 seconds (trim down), then the loss of altitude on takeoff (or landing) could be insurmountable. Sure, the pilots are supposed to turn off the system after the first time, but then that places the burden on them to get it diagnosed quickly and correctly the first time. I don't like it.

I'm going to stand on the side of those saying they won't fly the plane until this thing is fixed - and by fixed, I don't mean by pilot awareness. I think an immediate and effective software/hardware fix is necessary, or I would reluctantly say to ground the MAX. Let's hope Boeing can get it done quickly, and well.

fadecfault wrote:

Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

1 Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control aircraft pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged.
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer
trim wheel . . . . . . . . . . Grasp and hold
6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
7 Anticipate trim requirements.
- - - - - - - - - - - - - -

That procedure WILL stop MCAS or any trim from operating the trim motor. MCAS is also described in my MAX maintenance training manuals.

Hello all! I'm a long term follower of this great forum, globetrotting passenger for last 22 years. I have a few questions I hope someone could answer:

As I have understood, the auto trim normally controls the trim every now and then depending of the feedback from the AoA sensor. If there is an intermittent small problem in the AoA sensor, how would you differentiate that from normal auto trim function? As written in the above manual, as I understand it, if the problem goes away you continue without switching off the auto trim. How big the problem would need to be that you actually make the decision that this is a runaway trim and switch it off? Could it be that the AoA sensor problems were small in the beginning, not big enough to make the decision to switch off until the big fault came and activated the new stall protection which the pilots had no time to react?

According to the earlier emails, there was a problem in the AoA sensor and it was replaced. Looks like changing the sensor did not help. Is there a possibility that the cabling from the sensor to the computer is damaged? Is the sensor signal analogue or digital? Is there a possibility that the measuring computer itself is faulty? Maybe the fault reproduces only during flight due to vibration, temperature etc? Are these kind of problems common in aircrafts? Would these kind of faults be detected during regular maintenance of an AoA sensor?

well I guess in this case, Every doomed passenger's family and Lion Air can sue boeing and ask Boeing to be the sole primary responsibility for the crash, not Lion Air. It's an easy case to win