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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 1st May 2019, 17:37
  #4701 (permalink)  
 
Join Date: Feb 2015
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Originally Posted by gums View Post
Salute!

I shall stick with my interpretation of the reason MCAS was implemented.

It was to counter a nose up pitch moment.

If all it had to do was stiffen or increase back stick, there would not have been two crashes where the stab trimmed so far down that recovery was a big problem. Oh yeah, then the 5 sec pause and here we go again.

I would love to have Driver or another 737 jock fly the MAX with no MCAS and pull until the stall shaker. Let us know if the stick got lighter and if it was a problem. Real plane, not a sim.

PLease see the other forum where the pitch versus AoA charts are shown/discussed. and somewhere here we have the same chart.

Gotta see the dentist. So later..
...
Gums...
Hi Gums, Hope the dentist was kind... Saw the charts before, ta.

I think the point is:

- As they say on the news (and here for once they are right...) MCAS is a function which can/will push the nose down whereas

A feel increase mechanism will make pulling back harder - but won’t push the nose down.

Now I know which I would rather have.

Let’s imagine that such a system had been fitted instead of MCAS in the three AoA anomaly cases which we have discussed. What would have happened?

All the accompanying warnings for stall and speed disagree etc. would still have gone off. While the crew were sorting this out - with or without autopilot, with or without flap - there would have been no further distraction except a stiffer pull force, which could have been trimmed out as required. No big hand forcing the flight path down - no trim “runaway”.

The chances for survival would have been good, crew skills here or there I reckon.

Greetings, B
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Old 1st May 2019, 17:41
  #4702 (permalink)  
 
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Originally Posted by bill fly View Post


Hi Gums, Hope the dentist was kind... Saw the charts before, ta.

I think the point is:

- As they say on the news (and here for once they are right...) MCAS is a function which can/will push the nose down whereas

A feel increase mechanism will make pulling back harder - but won’t push the nose down.

Now I know which I would rather have.

Let’s imagine that such a system had been fitted instead of MCAS in the three AoA anomaly cases which we have discussed. What would have happened?

All the accompanying warnings for stall and speed disagree etc. would still have gone off. While the crew were sorting this out - with or without autopilot, with or without flap - there would have been no further distraction except a stiffer pull force, which could have been trimmed out as required. No big hand forcing the flight path down - no trim “runaway”.

The chances for survival would have been good, crew skills here or there I reckon.

Greetings, B
this for me is THE best post on this entire thread

G
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Old 1st May 2019, 17:47
  #4703 (permalink)  
 
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Originally Posted by alf5071h View Post
Pitch / power is an aspect of UAS drill, which was diagnosed immediately after takeoff and managed by the crew as they saw the situation.


Please show us where in the preliminary report timeline that the crew diagnosed the UAS, and took any action that was consistent with following the UAS NNC checklist.
https://leehamnews.com/wp-content/up...MAX-ET-AVJ.pdf
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Old 1st May 2019, 17:50
  #4704 (permalink)  
 
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Salute!

Great discussion.
I gotta get one of our test pilot golden arms to talk a bit.
While I go thru old stuff discussing the pitch moments of the 737, I will leave you a few thots.

Unless you only wish to change what the pilot feels, you do not screw around with the largest aero surface on the plane besides the main wing. You screw around with the artificial feel system. GASP!!

Pushers are not a really neat fix when all you want to do is reduce the nose up pitching moment. You have to deal with the aero as well as the artificial feel system.. And before more research and consulting, I comment:

The Airbus FBW in 320 plus does not give a rat’s about the “feel” close to a stall AoA. You can command max or min and that stick has the same spring force as if you were in a dogfight in the F-22 or Typhoon. Huh? It was certified because the basic aero met the criteria and the plane design would do just fine with ropes, levers, pulleys, pushrods and such. That was not what I flew in the Viper, due to inherent stability designed in from day one. But I can use my experience using a stick with zero feedback, and it commanded roll rate and gee according to how many pounds I exerted on the thing (Airbus stick is displacement mainly, but Viper was all pressure sensors)

PEI..... We need some test community inputs to this discussion

Gums.....
P.S. tanks for tolerating this old fart that flew ropes, pulleys and then hybrids and finally no sierra FBW that had zero mechanical anything before some here were born.






Last edited by gums; 1st May 2019 at 17:58. Reason: added comment
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Old 1st May 2019, 17:59
  #4705 (permalink)  
 
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Who owns the CVR and FDR data?

A complete CVR transcript would shed a lot of light on the question of whether or not an MCAS runaway is beyond the capability of the average MAX pilot. A complete FDR dataset would fill in some of the blanks that continue to cause confusion and argument. Many posters say, "Let's wait for the final report."

Waiting is not an acceptable option for Boeing and their MAX-customers.

Does anyone know if Boeing/FAA/NTSB have seen the complete CVR and FDR data?

The Ethiopean government's secrecy in the early days of the investigation suggest that they are not in the mood for sharing. International law entitles them to run the investigation. Does it also allow them to hide the data?

YYZjim
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Old 1st May 2019, 18:01
  #4706 (permalink)  
 
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Not a 737 driver so I have no vested interest in defending my plane/livelihood. Also neither American nor European, so I could not care less about defending my "team". What I am is a frequent traveller who would prefer not to become a smoldering crater in the ground -- preferably not even if I am flying on a plane flown by the most poorly trained, least-skilled and most sleep-deprived (but properly licensed) pilot.

I've read this whole thread and then some, and thus far my reading of the facts of these incidents is as follows:

1. (Fact) Boeing was caught with their pants down by the A320neo and needed to come up with a quick 737 update with better fuel economy (i.e. with minimal engineering changes).

2. (Fact) Rather than produce a clean-sheet design or update the 737 undercarriage/wings to incorporate an extended main landing gear, Boeing extended the nose gear and bolted on larger engines by moving the engines forward relative to COG, in spite of the negative impact that this had on aircraft stability/handling.

3. (Fact) The 737 stabilizer has much greater vertical authority than the elevator (I have seen estimates of about 3x as much)

4. (Fact) Due to the enlarged and forward-positioned engines, the Max exhibits poor aerodynamic/flight handling characteristics (tendency to pitch up) at high AOA when approaching stall. As communicated by at least one purported Boeing engineer much further up this thread (post 1000 or thereabouts?), this tendency to pitch up is so extreme that elevator input alone would not have been sufficient to make the aircraft adequately controllable, hence why a stick pusher was considered and rejected.

5. (Speculated) For the same reason, once in a stall, the 737 Max is quite likely to be extremely difficult to bring back under control through normal control surface inputs, without the rapid application of an extreme amount of stab trim (i.e. by MCAS). (Has anyone flown a Max into a stall at MTOW/rear COG and would they be able to provide input on whether it is possible to bring it back under control without trim input/MCAS?)

6. (Fact) The FAA/other authorities require positive elevator feel at high AOA to provide stall protection.

7. (Fact) MCAS is designed to provide positive elevator feel at high AOA to meet regulator requirements.

8. (Fact, deduced from 6 and 7) MCAS provides stall protection.

9. (Fact) The certified limit of MCAS authority (one burst of 0.6 deg) was also not sufficient to make the aircraft adequately controllable at high AOA. Boeing increased MCAS authority to 2.5 degrees per cycle, with an unlimited number of allowed cycles, without informing regulators/obtaining certification.

10. (Fact) The FAA was so understaffed/feckless that they did not discover/were not made aware of this severe deviation from certification.

11. (Fact) Based on various pilot reports and according to archaic 737 manuals and flight training, past a certain limit that is inversely related to airspeed, manual authority over trim is impossible for pilots of less than super-human strength, so e trim is the only option available.

12. (Fact) Boeing shrunk the size of the Max trim wheel, reducing leverage and further increasing strength required to manually trim. They failed to inform regulators of this change.

13. (Fact, deduced from numbers 10 and 3) Under certain portions of the flight envelope, pilots lose all vertical authority without electric trim.

14. (Opinion) Based on its essentiality to maintaining vertical authority under all allowed portions of the flight envelope, electric trim should be considered a safety-critical component and should be subject to all of the requirements thereof (e.g. redundant computers, motors, etc.)

15. (Fact) Boeing redesigned the cutoff switches to make it impossible to disable MCAS without also disabling e trim. They then failed to describe these changes in the manual or provide this information to pilots.

16. (Unverified, but extremely likely) Based on the inconsistent application of upward electric trim by the pilots during the two accidents, something was likely preventing the pilots from continuously applying upward trim. If your life is flashing before your eyes and you are battling to get your aircraft to climb, your thumb is going to be glued to the trim switch, not making the bare minimum in small (and inconsistent) blip applications. As far as I know it has not been conclusively reported, but it appears that based on the trim traces that MCAS is in fact capable of overriding thumb trim and not the other way around, despite claims to the contrary.

17. (Speculation) Many have speculated that the electric trim motor is also incapable of controlling the stabilizer under certain portions of the flight envelope (e.g. high speed, extreme trim, opposing elevator). If this is true, then there are actually portions of the flight envelope in which pilots lose all vertical authority even if electric trim is operational.

18. (Opinion) If there are regions of the 737 flight envelope (e.g. extreme trim, opposing elevator) under which pilots lose vertical authority, the whole 737 fleet, both maxs and NGs (assuming that they are also affected by the same issue), should be grounded until such a time as trim deflection is mechanically limited to prevent entry into these uncontrollable regions of the flight envelope.

19. (Fact) Boeing did not advise pilots of the limits of manual trim authority or the need to e trim to neutral before cutting the trim switches.

20. (Fact) Boeing decided to base the activation of MCAS on a single AOA sensor (rather than making use of the two installed sensors) and a single computer, without even basic sanity checking.

21. (Fact) A large number of recent reports have identified safety-critical manufacturing defects and foreign object debris in recently-constructed Boeing aircraft as a result of lax manufacturing standards, and articles from yesterday indicate that a whistleblower reported to the FAA on April 5th that FOD had resulted in damage to Max AOA wiring in at least one instance.

22. (Fact) Boeing did not inform airlines or pilots about MCAS, did not include it in the manual, and did not provide any MCAS related training.

23. (Fact) Boeing chose not to provide an aural/visual MCAS activation warning.

24. (Fact) Boeing opted to sell the AOA indicator display as an optional extra rather than a built-in safety feature.

25. (Fact) Boeing disabled the AOA disagree warning for customers who did not purchase the optional AOA indicator display. Previous 737 models had functional AOA disagree warnings. As reported recently by the SWA pilots assoc, Boeing did not inform airlines/pilots of this change.

26. (Fact) Boeing did not make or arrange for the production of an adequate number of Max simulators, hence the extreme resistance to any changes that would require sim training.

27. (Fact) Pilots did not receive any information about MCAS or sim/flight training for dealing with a possible MCAS activation prior to these incidents (they did not even know that the system existed).

28. (Inferred based on events) The incident pilots were inadequately trained to handle and responded very poorly to MCAS activation incidents. (Note: is it the pilots' fault that they were inadequately trained on a system that they did not know existed on simulators that were not available?)

29. (Fact) After the Lion air accident, Boeing provided only the bare minimum in information regarding MCAS and refused to acknowledge any problem with the plane, placing the blame entirely on the dead pilots.

30. (Fact) After the Ethiopian accident, Boeing resisted efforts to ground the aircraft and refused to acknowledge any problem with the plane, again placing the blame entirely on the dead pilots.

31. (Fact) After the Ethiopian incident and following a meeting between Muilenburg and Trump, Trump's FAA stooge resisted requests to ground the Max.

32. (Fact) Only after foreign regulators began grounding the Max en masse did the FAA also follow suit and ground the Max.

33. (Fact) Boeing, as evidenced by Muilenburg's recent press conference, still refuses to acknowledge any problem with the plane, and continues to place blame solely on the dead pilots. Meanwhile they are working on a software "improvement" for MCAS, without any reports of hardware fixes in the works.

Conclusion:

In my opinion, Boeing has acted disgracefully in this situation and should be prosecuted criminally for manslaughter (perhaps this is an opportunity for Barr to prove that he is not a Trump stooge). Meanwhile the FAA has been completely compromised and corrupted by the kleptocracy that is taking over America. These are systemic failings rather than a one-off incident, and they raise the question of how many other similar failures remain lurking in the shadows due to negligent management practices and oversight in a country that is rapidly losing any respect for the rule of law. No outcome short of a complete (and transparent) overhaul of Boeing's safety culture, prosecution and incarceration of senior management, and possibly even a break-up of the company (e.g. splitting off commercial aviation from defense) will make me comfortable flying on any recently-produced Boeing metal. I'll be putting my money where my mouth is by exclusively booking Airbus until these changes are made. I'm not holding my breath, so it looks like I'll be flying Airbus for some time to come.
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Old 1st May 2019, 18:06
  #4707 (permalink)  
 
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Edit - Gums (and also Bill Fly) - just seen your Post 4706 when I Posted - but as I've written this forgive me for Posting anyway. Exactly! You and I are together I think on this! (If I may be so bold as to assume that?)

Originally Posted by AAKEE View Post
...........

There is a pitch up moment from the engine nacell’s at high alfa but it is allways less than the pitch down coming from the CG being forward of the centre of pressure center. The nacelles pitch up moment ease the elevator work to pitch up /decrease speed, making the stick force gradient to low.
Never flown (or fixed) Boeings but, given the above which is what I think we all agree is the issue – not enough stick force at higher AoA to meet Certification due to the pitch-up moment generated by the donks homes - then surely this Thread (B737 Feel And Centering Unit) describes where the solution should have been implemented to “reprofile” Elevator Feel but for Speed and AoA rather than just for Speed – in other words, add in a bit more "aft" stick Q-resistance at high AoA.

While, ideally using a dual AoA system, if Boeing insisted on just one AoA feed, all you would have is a slightly erroneous “feel profile” at higher AoAs with a U/S AoA system (auto cured when the AoA system is fixed). This would seem far more manageable (tho it would be out of Certification limits in purist terms on AoA fail) than the MCAS erroneously trimming AND which materially affects the flightpath (and I’m deffo going to avoid any discussions on whether or not that was handleable by an “average crew” - whatever one of those is – but we do have 2 jets down with awful consequences for 100’s of people so the complete system (incl aircrew and bits and software) fell over twice).

Is that assessment correct and did MCAS seem to provide Boeing with a simpler/cheaper solution to “emulate” a change in Q rather than make changes to the Elevator Feel Computer (EFC) in it’s role as described by IFixPlanes? I can’t really recall this discussion of the EFC anywhere. Or, since that Thread was wayyy back in 2010, does the EFC no longer exist – but since Q-feel has been around for ever really - something still does that job surely. Boeing seems to be trying to keep the aircraft away from high AoA so that we don't get uncertifiable Q issues rather than sorting Q so it's certified at all AoAs. I can’t recall where the schematics appear in this thread re an EFC but just a thought … and happy to crawl back into my box if talking utter tosh! Won’t be the first time for me!

Originally Posted by AAKEE View Post
...........

Gums, you have my respect for many excellent posts and a very good carreer! Thumbs up :-)
And “Here, here!” - always good to see Gums chipping in for the reasons above!

Last edited by Hot 'n' High; 1st May 2019 at 18:25.
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Old 1st May 2019, 18:20
  #4708 (permalink)  
 
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Originally Posted by Avionista View Post
737Driver and his cohorts seem intent on diverting attention towards alleged deficiencies in the airmanship of the crews of the two 737 max aircaft that crashed rather than dealing with the real villains of the piece, namely, the FAA and Boeing.
This is a hazardous attitude which is harmful to aviation safety. Pointing out that the pilot's actions were seriously deficient in no way exonerates Boeing. It is clear that Boeing's design of MCAS appears to be the primary cause of both accidents, it is unacceptable, it needs to be fixed, and it is being fixed. However you cannot fix only one deficient link in an accident chain and declare "Mission Accomplished!" like you are George W. Bush on an aircraft carrier after the first battle in the Iraq war. ALL deficiencies that contributed to the accident need to be assessed to determine if corrective action is needed. This could include the regulations that the aircraft is designed to, the oversight of the certification and change management process by the regulator, the content and method of delivery of the NG to MAX transition training, the schedule, recency, and frequency of any recurring training, the service bulletin and FCOM/QRH deployment procedures at the airline, and the maintenance and post-maintenance test procedures at the airline. (Lionair - so far there have been no indications that Ethiopian performed maintenance on the AOA or ADIRU)

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Old 1st May 2019, 18:59
  #4709 (permalink)  
 
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SDR database lists 42 AoA faults on all Boeings in last 15 years

Some posters in this thread have wondered if reliability stats exist for AoA sensors.

Apparently the FAA mandates that for US operators all aircraft faults that require maintenance actions are to be reported within 28 days of occurrence. (Yes, for all items big or small, even for the simplest things such as loose exit signs or a flat battery pack in a FA emergency flashlight!)

CNN (yep, them) went hunting through the public database looking for evidence.

“The FAA has received at least 216 reports of AOA sensors failing or having to be repaired, replaced or adjusted since 2004, according to data from the FAA’s Service Difficulty Reporting website.
Those reports, about one-fifth of which involve Boeing planes, include incidents in which AOA sensors were frozen, improperly installed, struck by lightning or even hit by flying birds. In some cases, faulty sensors led to stall warnings, forcing pilots to abort takeoffs or perform emergency landings.”
More alarming in the CNN article with video is the claim that unnamed Boeing sources (ex. a former MAX test pilot) report that the 737MAX series were not tested against AoA failure: "I don't think we appreciated the ramifications of a failure of an AOA probe."
Goes on...(in the expected style).

FAA's Service Difficulty Reporting website (if you're keen to explore there's a Search Reports link in the left column on the site)
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Old 1st May 2019, 19:22
  #4710 (permalink)  
 
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Originally Posted by slacktide View Post
................ Pointing out that the pilot's actions were seriously deficient in no way exonerates Boeing. .............. This could include the regulations that the aircraft is designed to, the oversight of the certification and change management process by the regulator, the content and method of delivery of the NG to MAX transition training, the schedule, recency, and frequency of any recurring training, the service bulletin and FCOM/QRH deployment procedures at the airline, and the maintenance and post-maintenance test procedures at the airline. (Lionair - so far there have been no indications that Ethiopian performed maintenance on the AOA or ADIRU)
Agreed! It's called "Systems Engineering" and, in their System Safety Assessment, Boeing assumed a level of performance of the 3 elements of their system Hardware, Software and Humanware all of which was deficient in that all elements did not meet Boeings assumed performance levels on several occasions - hence the holes lining up twice in the Safety Assessment. The holes are meant to line up once every x,000,000 hrs - but they lined up twice in quick succession - the assumed performance levels (reliability) did not provide the level of Safety required - or that it was not fully assessed - a point SFLstu notes above with that quote "I don't think we appreciated the ramifications of a failure of an AOA probe." That is a worry if true! Irrespective of "Well, they [the crew] should have been able to....." I personally suspect the next alignment of all 3 elements failing (one could argue MCAS worked as designed but the design was too "severe") would not have been far away - hence the grounding so we'd have time to consider what needs fixing - as you say, more than just a bit of code. The fact that, IMHO, (and that of at least a couple of other people in recent Posts) that the solution was applied in the wrong area worries me too!

As you say, all elements of the "system" need to be addressed - but, if the Q-system is where the solution should by rights be - sadly that does not seem to be likely. So, the other elements will have to be able to mitigate a bigger Risk(?) posed by MCAS solution than by a Q-system change. Would "Best of a bad job!" be too strong a phrase? And, as you say, not only do we have to make the MAX "system" safe (which we can do), we have to (re)learn how it could have been done better. Using 2 dreadful crashes to decide we as an Industry had got things wrong is not the way to do things. We should all think long and hard where, in our own jobs, what the effects could potentially be if we don't play our part in whatever we are involved in (see the thread in the Military forum dealing with Airworthiness for example). Been in aviation 41 years now and the only progress I've made is, each year, I realise that I know even less than I thought I knew last year!

Off to find a non-asbestos fire blanket to hide under so as avoid the flaming I'm sure I'll Rx over this! Oh, and decide whether I'm just so "unsafe" I should retire immediately!

Last edited by Hot 'n' High; 1st May 2019 at 19:24. Reason: Odd "y" floating around!
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Old 1st May 2019, 19:25
  #4711 (permalink)  
 
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Originally Posted by SLFstu View Post
Some posters in this thread have wondered if reliability stats exist for AoA sensors.

Apparently the FAA mandates that for US operators all aircraft faults that require maintenance actions are to be reported within 28 days of occurrence. (Yes, for all items big or small, even for the simplest things such as loose exit signs or a flat battery pack in a FA emergency flashlight!)

CNN (yep, them) went hunting through the public database looking for evidence.
Similar links have been posted on the forum. The Washington Post previously did a count over a different timeframe, and gets to the point. My emphasis added: https://www.washingtonpost.com/business/economy/sensor-cited-as-potential-factor-in-boeing-crashes-draws-scrutiny/2019/03/17/5ecf0b0e-4682-11e9-aaf8-4512a6fe3439_story.html
Angle-of-attack sensors have been flagged as problems more than 50 times on U.S. commercial airplanes over the past five years, although no accidents have occurred over millions of miles flown, according to reports made to the Federal Aviation Administration’s Service Difficulty Reporting database. That makes it a relatively unusual problem, aviation experts said — but also one with magnified importance because of its prominent role in flight software.
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Old 1st May 2019, 19:33
  #4712 (permalink)  
 
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Originally Posted by Lost in Saigon View Post
The consensus is WRONG. Boeing clearly states that electric trim will STOP and even REVERSE unwanted MCAS operation.
Unfortunately, Boeing cannot be relied on as providing full and accurate information. The investigation and further legal actions will have to resolve how the systems actually works. There may be an assumption that electric trim input will override MCAS authority but it is not entirely clear how the system operates with conflicting demands. How the authority is resolved during conflict will have to be resolved fully. There are software, electrical, mechanical and aerodynamic elements to the investigation of the trim system.

Obviously, continuing to rely on conflicting AoA sensors is inherently wrong. MCAS should be disabled automatically if the primary sensor information is known to be unreliable. Boeing were aware of the defect even before the Lion Air incidents, or even at the design stage, but chose not eliminate the defect. The question is why did Boeing act in that way and to what degree they tried to conceal or underplay the issues. The Max MCAS system is poorly designed and inherently dangerous. It has passed through many hands, but for some reason, obvious problems were not addressed or may have been concealed. It is certainly possible that persons in Boeing and in the FAA will be held to account. In those circumstances, there is good reason doubt the accuracy of information that Boeing provides.

While accident investigations generally avoid attributing or proportioning blame, the courts will have to do precisely that. No doubt the pilots could have done better, but were not the primary cause. Boeing are facing some very difficult questions along with the FAA.
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Old 1st May 2019, 19:54
  #4713 (permalink)  
 
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Originally Posted by SLFstu View Post
Apparently the FAA mandates that for US operators all aircraft faults that require maintenance actions are to be reported within 28 days of occurrence. (Yes, for all items big or small, even for the simplest things such as loose exit signs or a flat battery pack in a FA emergency flashlight!)
This is not quite correct. Only a subset of items and events are subject to mandatory SDR reporting. The applicable regulation is 14 CFR Part 121.703. It is DEFINITELY not applicable to all items big or small. A loose exit sign, or a flat battery pack in a flashlight would require an SDR because they are part of the passenger emergency evacuation lighting systems, which is listed in 121.703. A loose bathroom sign or a flat battery pack in the in-flight entertainment system would not require an SDR.

An inoperative AOA sensor that did not require the crew to take an emergency action would not require a SDR to be submitted. I read a few of the AOA SDR reports, and they were all associated with conducting a rejected takeoff. The takeaway here is that AOA failure rates may be higher than indicated by the SDR database.

edit: Technically, even an AOA failure that caused an RTO would not require an SDR to be submitted. Bullet (16) would be applicable - "Aircraft components or systems that result in taking emergency actions during flight", and 121.703 defines "during flight" as after the wheels have left the ground.

Last edited by slacktide; 1st May 2019 at 20:18.
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Old 1st May 2019, 19:55
  #4714 (permalink)  
 
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:
Originally Posted by Lost in Saigon
The consensus is WRONG. Boeing clearly states that electric trim will STOP and even REVERSE unwanted MCAS operation.
Originally Posted by wheelsright View Post
Unfortunately, Boeing cannot be relied on as providing full and accurate information. The investigation and further legal actions will have to resolve how the systems actually works. There may be an assumption that electric trim input will override MCAS authority but it is not entirely clear how the system operates with conflicting demands. How the authority is resolved during conflict will have to be resolved fully. There are software, electrical, mechanical and aerodynamic elements to the investigation of the trim system.
...
...
.
Alll 3 of the FDR traces clearly show MCAS kicking in ~5 seconds after the last manual electric trim. The ET trace also shows MCAS stopped in it's second run by pilot trim at 05:40:27. This is exactly as Boeing describes it.

On a separate note, it is only the manual (wheel) trim that is suspected of being inoperable with high aero loads. (not just at >VMO).
The electric trim will work, and even if the motor stalled the inputs would still show on the FDR, in the same way that the MCAS input in ET at 05:40:15 had no effect on trim due to stab trim cutout.

The pilots electric trim inputs (if any) would not show due to the wiring of the cutout switches that remove 28Vdc to them.

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Old 1st May 2019, 19:55
  #4715 (permalink)  
 
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Everyone who says that ANU input on the tumb switches will reverse MCAS is right.

However, the question is whether training was remotely adequate to address the AND authority of MCAS, which demanded an unusual amount of ANU trim in the teeth of stick-shake, AoA warnings and UAS advisory. Anyone is free to correct me, but it seems as if an unusual amount of thumb-switch ANU would be needed.

Meanwhile, the intermittency of MCAS inputs seems to be tailor-made to look unlike a runaway. It certainly doesn't serve to decrease confusion.
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Old 1st May 2019, 20:34
  #4716 (permalink)  
 
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Originally Posted by LowObservable View Post
However, the question is whether training was remotely adequate to address the AND authority of MCAS, which demanded an unusual amount of ANU trim in the teeth of stick-shake, AoA warnings and UAS advisory. Anyone is free to correct me, but it seems as if an unusual amount of thumb-switch ANU would be needed.
This is one thing that has confused me in both accidents - not using the manual trim switches to return the aircraft to a fully trimmed condition. Even in a private pilot training syllabus, this is taught and demonstrated as part of the very first introductory flight lesson, and it is not a particularly difficult concept to grasp (but mastering it takes time...) Over time recognizing when you will need to trim, and how much trim is needed to adjust the control pressure, just becomes instinctual.

Can any of our resident 737 pilots comment on use of manual electric trim and control pressures in that aircraft? Is the process similar to on a light aircraft, where you trim until you are satisfied that the aircraft can be controlled with only light fingertip pressure? How does an active stickshaker affect your ability to perceive control pressure?
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Old 1st May 2019, 21:04
  #4717 (permalink)  
 
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Originally Posted by Lost in Saigon View Post
I think your interpretation is wrong.

My understanding is that MCAS was implemented ONLY to satisfy FAA Section 25.173

* * *

"MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation."
I've been thinking about this - and don't believe it can be an accurate statement of the purposeful design of the system. Here's why . . .

MCAS will, when data input dictates, trim AND. It will do so for 9 seconds or so - and then take a 5 second break. When it's taking its break - it's not fulfilling the purpose of 25.173 - right?

If the purpose of the system is to compensate for stick feel - it wouldn't take a break - because the lift generated by the cowlings doesn't take a break.

If tdracer is still around on this topic - I'd like to know how the designed 5-second stand down plays into the purposeful design of the system. It just doesn't make sense to me.

WillFlyForCheese is offline  
Old 1st May 2019, 21:21
  #4718 (permalink)  
 
Join Date: Aug 2012
Location: Scotland
Age: 49
Posts: 155
Why MCAS to start?

Regardless of whether pilot, training, sensor, computing, hardware or maintenance error caused the incident, to go back to square one I'm still interested in why MCAS was implemented in the 1st place to resolve a feel issue(?).

I understand why the cowlings are larger.

I understand why the cowlings have been repositioned.

I understand why the cowlings increase lift.

I believe that certification requires increasing stick forces at increasing AOA.

I still do not understand why MCAS was the resolution as I still do not understand why the driving one of the 737's most powerful control surface was considered as a suitable remedy to what in my understanding is a pilot perception requirement that certification demands. There are other methods of doing this that cannot put an aircraft in jeopardy.

PLEASE someone tell me that my train of though is wrong, or if it isn't why was MCAS seen by Boeing & the regulators as a suitable resolution to the issue?


I've asked as much a few times previously without reply - I'm genuinely interested & if it wasn't for the fact that there are various MAX threads on the go I would start one specifically on this question.
Thrust Augmentation is offline  
Old 1st May 2019, 21:38
  #4719 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 58
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Originally Posted by WillFlyForCheese View Post
I've been thinking about this - and don't believe it can be an accurate statement of the purposeful design of the system. Here's why . . .

MCAS will, when data input dictates, trim AND. It will do so for 9 seconds or so - and then take a 5 second break. When it's taking its break - it's not fulfilling the purpose of 25.173 - right?

If the purpose of the system is to compensate for stick feel - it wouldn't take a break - because the lift generated by the cowlings doesn't take a break.

If tdracer is still around on this topic - I'd like to know how the designed 5-second stand down plays into the purposeful design of the system. It just doesn't make sense to me.
There are two followup aspects to your question, depending on the version of MCAS 1.0 and MCAS 2.0:
- MCAS 1.0 was designed to satisfy the criteria that you describe, though not smoothly, due to the 5 second pause.
- MCAS 2.0 may remove the option of repeated trim during the same high AOA "event", depending on the definition of event. This would not satisfy the 25.173 criteria, if it allowed the pilots to do a second pull into the high AOA region, after interrupting MCAS by blipping the stabiliser trim switches.

Long ago I posted this assertion: It is logically impossible to design a system that satisfies both limited MCAS activation and 25.173 criteria simultaneously. One of the two limits has to be broken in some scenarios, for example pilots repeatedly entering the high AOA condition. I have not seen any evidence to contradict my assertion.
GordonR_Cape is online now  
Old 1st May 2019, 21:50
  #4720 (permalink)  
 
Join Date: Dec 2014
Location: USA
Posts: 33
Originally Posted by WillFlyForCheese View Post
I've been thinking about this - and don't believe it can be an accurate statement of the purposeful design of the system. Here's why . . .

MCAS will, when data input dictates, trim AND. It will do so for 9 seconds or so - and then take a 5 second break. When it's taking its break - it's not fulfilling the purpose of 25.173 - right?

If the purpose of the system is to compensate for stick feel - it wouldn't take a break - because the lift generated by the cowlings doesn't take a break.

If tdracer is still around on this topic - I'd like to know how the designed 5-second stand down plays into the purposeful design of the system. It just doesn't make sense to me.
As the trim moves AND, the pull back feel of the column will become heavier. So in that sense, some AND trim can neutralize the tendency for a lighter feel at higher AoA, bringing the feel into certification compliance. Once the trim has moved enough to offset the pitch-up moment from the engine nacelles, it does not need to continue to move AND and MCAS would, in normal circumstances, stop its trim input. The problem in the two accidents is that the AoA was wildly divergent from normal range due to presumably damaged or missing AoA vane. That is what triggered MCAS to make the full 9-second/2.5 degree AND stab movement. In ordinary manual light, with correct AoA data, MCAS would presumably be making much smaller inputs.
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