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Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 6:34 pm

Thank you "fadecfault" and "PixelFlight"
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 6:41 pm

Backseater wrote:
IMHO FDR & CVR are not the issues. They will clearly show that MCAS was active...

It is true that there is more that goes into the Preliminary Report than just FDR and CVR. But I think the FDR can reveal much more context of how the accident played out. I'm interested in seeing data like AOA values, flap settings, electric trim input, stick shaker, control column forces, etc.
 
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Finn350
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 6:59 pm

Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 7:47 pm

Finn350 wrote:
Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.

If it consists of only 2 pages’ m they did not want to release it on April fool day!
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 7:50 pm

Finn350 wrote:
Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.

If it consists of only 2 pages, maybe that’s why they did not want to release it on April fools day! :banghead:
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:07 pm

Finn350 wrote:
Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.

The Lion Air JT610 Preliminary Report was delivered within a month, and was ~70 pages with lots of technical data, including FDR graphs. I'm hoping for more than 2 pages of basic facts.
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:17 pm

jollo wrote:
Statement 5: Trim cut out checklist is flawed
The standard response to just hit the stabilizer cutout switches and manually trim is actually flawed. If the nose has been pushed down by significant mistrim (nose down stabilizer, nose up elevator), and as airspeed increases, it may not be possible to trim the stabilizer manually nose up without letting the elevator go to a neutral position. The reality, under the MCAS runaway scenario, trimming nose up immediately stops MCAS as well as trims the stabilizer back towards an in-trim position. At that point, you would be best off to cutout the stabilizer.

The runaway trim checklist tells you to do this. Where is the flaw?

Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.
Phrogs Phorever
 
Heinkel
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:26 pm

Backseater wrote:
Are the maintenance records for that aircraft good enough to be released:
- serial numbers of the AoA sensors installed? (by the way, did they find them in the debris? They should have!)
- history records of the AoA sensors (source, repairs, ...)
- detailed records of the installation and test procedure of both sensors on that particular a/c
And if their maintenance records are not good enough, what will they do?


These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:33 pm

flybucky wrote:
Finn350 wrote:
Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.

The Lion Air JT610 Preliminary Report was delivered within a month, and was ~70 pages with lots of technical data, including FDR graphs. I'm hoping for more than 2 pages of basic facts.

I would speculate that the delay in issuing the report is more likely related to giving Boeing the opportunity to review the draft rather than anything else.

Perhaps they are trying to get 'make a safe plane safer' in the text somewhere?
 
fadecfault
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:37 pm

Heinkel wrote:
Backseater wrote:
Are the maintenance records for that aircraft good enough to be released:
- serial numbers of the AoA sensors installed? (by the way, did they find them in the debris? They should have!)
- history records of the AoA sensors (source, repairs, ...)
- detailed records of the installation and test procedure of both sensors on that particular a/c
And if their maintenance records are not good enough, what will they do?


These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?


Who says the fail time to time? Based on what data?
The views and opinions written here are my own and do not reflect those of my employer.
 
uta999
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:47 pm

XRAYretired wrote:
flybucky wrote:
Finn350 wrote:
Preliminary report will be something like two pages stating the basic facts. Maybe in a couple of months time we will get an interim report with more facts.

The Lion Air JT610 Preliminary Report was delivered within a month, and was ~70 pages with lots of technical data, including FDR graphs. I'm hoping for more than 2 pages of basic facts.

I would speculate that the delay in issuing the report is more likely related to giving Boeing the opportunity to review the draft rather than anything else.

Perhaps they are trying to get 'make a safe plane safer' in the text somewhere?


Two fatal accidents caused by exactly the same weak system put together on the cheap by amateurs.

Boeing should be adding “make an unsafe plane safer” in the text somewhere?
Your computer just got better
 
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speedbored
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:52 pm

dragon6172 wrote:
The runaway trim checklist tells you to do this. Where is the flaw?

Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.

Isn't that quote from the bulletin that Boeing issued after the Lionair crash, not the checklist?
 
Heinkel
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:53 pm

fadecfault wrote:
Heinkel wrote:
These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?


Who says the fail time to time? Based on what data?


There are reports in this forum about failure of AOA-sensors. There are even reports of failure of two sensors at the same time.

Most of these failures don't make the news. They were replaced and that's it. This is why I've asked, if someone has exact statictics about the failure rate of AOA-sensors.

And be sure, they fail.
 
PixelPilot
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 8:55 pm

uta999 wrote:
XRAYretired wrote:
flybucky wrote:
The Lion Air JT610 Preliminary Report was delivered within a month, and was ~70 pages with lots of technical data, including FDR graphs. I'm hoping for more than 2 pages of basic facts.

I would speculate that the delay in issuing the report is more likely related to giving Boeing the opportunity to review the draft rather than anything else.

Perhaps they are trying to get 'make a safe plane safer' in the text somewhere?


Two fatal accidents caused by exactly the same weak system put together on the cheap by amateurs.

Boeing should be adding “make an unsafe plane safer” in the text somewhere?

So you already know the cause??
Care the share lotto numbers for this week buddy?
 
Amexair
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 9:43 pm

jollo wrote:
morrisond wrote:
jollo wrote:
Cross-posting member rheinwaldner from the B737MAX Grounded Worldwide thread (@Admins: sorry for bending the rules, but this is relevant).

++++++++

Here we have some credible statements, which are not hearsay because the name of the source is known (Rick Ludtke, a former Boeing designer, who worked on the MAXs cockpit interfaces):

Source is the following full copy of the original WSJ article, which is behind a paywall:
https://www.marketwatch.com/press-relea ... quote_news

More from Ludtke here:
https://www.seattletimes.com/business/b ... _inset_1.1

More statements from the following two links:
https://www.satcom.guru/2019/03/regulat ... stems.html
https://www.satcom.guru/2019/03/aoa-van ... g-fix.html


Statement 1: Penalty charges based on training requirements




Statement 2: Pressure to implement no-additional-training solution


Statement 3: MCAS runaway hard to detect


And



Statement 4: After trim cutout, using the trim wheel may be inadequate to deal with the situation


Statement 5: Trim cut out checklist is flawed


The Boeing procedure in there bulletin released on Nov 6, 2018 was to use Electric Trim if necessary to return the plane to neutral or nose-up before hitting the cut-off switches if you did not want to use the manual system.


I believe you are intentionally focusing on a secondary detail to avoid addressing the gist of the statements above, which I find extremely troubling.

However, if you want to nitpick:
1) the stated Reason for the Nov 6th, 2018 bulletin (published after the Lion Air crash) is: "To Emphasize the Procedures Provided in the Runaway Stabilizer Non-Normal Checklist (NNC)", which is prefaced by this Condition: "Uncommanded stabilizer trim movement occurs continuously". Therefore the runaway stab NCC, and by extension the bulletin, should not apply to intermittent stab trim uncommanded movements (and mention of "repetitive cycles of uncommanded nose down stabilizer" in the "Background Information" section of the bulletin is confusing at best).
2) so basically Boeing was trying to tell pilots they have to use a procedure that calls for cutting off a malfunctioning servo but not too fast! - you first need to use that very servo to recover from an otherwise unrecoverable upset, and then you need to cut it off before it tries to kill you again. As a passenger, I would not want to fly on an airliner that relies on such procedures.



Thank you for sharing. Probably the most logical presumption of what may have gone wrong with this crash so far, in my opinion.
 
jollo
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 9:52 pm

dragon6172 wrote:
jollo wrote:
Statement 5: Trim cut out checklist is flawed
The standard response to just hit the stabilizer cutout switches and manually trim is actually flawed. If the nose has been pushed down by significant mistrim (nose down stabilizer, nose up elevator), and as airspeed increases, it may not be possible to trim the stabilizer manually nose up without letting the elevator go to a neutral position. The reality, under the MCAS runaway scenario, trimming nose up immediately stops MCAS as well as trims the stabilizer back towards an in-trim position. At that point, you would be best off to cutout the stabilizer.

The runaway trim checklist tells you to do this. Where is the flaw?

Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.


1) The wording is misleadingly bland. There's a big difference with:

Initially, control forces needed to overcome any stabilizer nose down trim already applied may exceed your ability to apply such forces. Electric stabilizer trim must be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Above [X] KIAS, manual stabilizer trim can be used after the STAB TRIM CUTOUT switches are moved to CUTOUT only if control column inputs are discontinued.


which, if the scenario described by Rheinwalder can actually occur, would have been a more accurate (or at least honest) wording.

2) The paragraph you quoted is not part of the Runaway Stabilizer Non-Normal Checklist in the FCOM, but only appears as a Note in page 2 of the bulletin issued by Boeing on Nov 6th 2018 (after the Lion Air crash) with this Reason: "To Emphasize the Procedures Provided in the Runaway Stabilizer Non-Normal Checklist (NNC)". Not to replace, nor to amend the checklist, but only to emphasize the need to do a NNC which, after "5 [...] STAB TRIM CUTOUT (both) ...... CUTOUT" only says "6 Stabilizer ...... Trim manually"

3) Anyway, the Runaway Stabilizer NNC is subordinated to this Condition: "Uncommanded stabilizer trim movement occurs continuously". The applicability to a scenario where uncommanded trim movements occur intermittently (as when MCAS is active) is moot at best.
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 11:04 pm

jollo wrote:

2) The paragraph you quoted is not part of the Runaway Stabilizer Non-Normal Checklist in the FCOM, but only appears as a Note in page 2 of the bulletin issued by Boeing on Nov 6th 2018 (after the Lion Air crash) with this Reason: "To Emphasize the Procedures Provided in the Runaway Stabilizer Non-Normal Checklist (NNC)". Not to replace, nor to amend the checklist, but only to emphasize the need to do a NNC which, after "5 [...] STAB TRIM CUTOUT (both) ...... CUTOUT" only says "6 Stabilizer ...... Trim manually".


I quoted the AD. Wording is probably the same.

I am confused by your argument that the pilots would read enough of the bulletin to know that uncommanded nose down inputs require complying with Runaway Stab NNC, but they don't read the bulletin enough to see the note about using electric trim to reduce control forces?
Phrogs Phorever
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 11:27 pm

Heinkel wrote:
Backseater wrote:
Are the maintenance records for that aircraft good enough to be released:
- serial numbers of the AoA sensors installed? (by the way, did they find them in the debris? They should have!)
- history records of the AoA sensors (source, repairs, ...)
- detailed records of the installation and test procedure of both sensors on that particular a/c
And if their maintenance records are not good enough, what will they do?


These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?

The Wright Brothers AoA sensor consisting of one hanging thread probably had a very good MTBF. Besides, the pilot could easily see before takeoff whether the AoA sensor needed replacement. Simple design, Murphy proofed!

A century or so later, many AoA sensors were using resolvers (to avoid contacts) but had become mechanically complicated. For instance, the 0861ED made by Goodrich looked like this:

Image

In 2008 two of those Goodrich sensors simultaneously froze in flight with similar AoA values. Through an unfortunate sequence of events stemming from the AoAs, the A320 D-AXLA crashed into a shallow area of the Med.
The BEA investigated and produced a thorough, 200 page report (BEA accident report dated 27 November 2008) which analyzes in great detail what probably happened to the sensors. They recovered the damaged sensors from under 40m of water, then disassembled and meticulously analyzed each of their components. Traces of water, muddy residues from sanding and repainting,... probably froze some bearings when at altitude. From the thermal image, it looks like the vane was nicely heated but the rest of the assembly was not, or not enough, just where the bearings were located. IMO that report is definitely a must read for anyone interested in AoA sensors!

Today, I suspect (because I could not find any internal description of the sensor internals) that the new Rosemount 0861FL1 is both clever, simple, and highly reliable if not tampered with. It should be lighter because it has neither gears nor coils. It has self-regulating heaters that do not require thermostats. It uses a static magnetoresistive sensor to detect the rotation of two opposite, permanent magnets that are on the same shaft as the vane. It can be calibrated by carefully positioning the magnets with respect to the sensor, or by using compensating values stored in EEPROM using the sensor's internal microprocessor. It can output a digital signal, or analog signals through a D/A converter to look like an old fashioned sensor e.g. modulated sin & cos. If anyone attempts to repair such a device, they have better know what they are doing, mechanically and electronically (analog & digital).

(My guess is based on the unproven assumption that the new 0861FL1 implements what is described in the WIPO patent WO 01/77622 A2 filed by Rosemount Aerospace on 18 October 2001. That patent protects them in most countries around the world.)
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 01, 2019 11:38 pm

Backseater wrote:
Today, I suspect (because I could not find any internal description of the sensor internals) that the new Rosemount 0861FL1 is both clever, simple, and highly reliable if not tampered with. It should be lighter because it has neither gears nor coils. It has self-regulating heaters that do not require thermostats. It uses a static magnetoresistive sensor to detect the rotation of two opposite, permanent magnets that are on the same shaft as the vane. It can be calibrated by carefully positioning the magnets with respect to the sensor, or by using compensating values stored in EEPROM using the sensor's internal microprocessor. It can output a digital signal, or analog signals through a D/A converter to look like an old fashioned sensor e.g. modulated sin & cos. If anyone attempts to repair such a device, they have better know what they are doing, mechanically and electronically (analog & digital).

(My guess is based on the unproven assumption that the new 0861FL1 implements what is described in the WIPO patent WO 01/77622 A2 filed by Rosemount Aerospace on 18 October 2001. That patent protects them in most countries around the world.)

Thanks Backseater for all the details.
Is there redundancy for the electronic inside the AoA sensors ?
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 1:12 am

PixelFlight wrote:
Is there redundancy for the electronic inside the AoA sensors ?

I doubt it. 2 EEPROMS maybe?
I would write two copies of the configuration and calibration parameters to memory with a hash code, to ensure their validity when the sensor restarts.
And if the microprocessor cannot find a good set, it has no reason to fail high. 0 would prevent MCAS from being triggered.
Of course a constant 0 could never pass the post-install test procedure when it is carried out as required.

Notice also that a microprocessor based AoA with a digital output channel should be very happy to talk to digital avionics. Including outputting the AoA S/N so that it can be written to the FDR. But that connection does not exist today, because it did not exist before!
 
jollo
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 9:41 am

dragon6172 wrote:
jollo wrote:

2) The paragraph you quoted is not part of the Runaway Stabilizer Non-Normal Checklist in the FCOM, but only appears as a Note in page 2 of the bulletin issued by Boeing on Nov 6th 2018 (after the Lion Air crash) with this Reason: "To Emphasize the Procedures Provided in the Runaway Stabilizer Non-Normal Checklist (NNC)". Not to replace, nor to amend the checklist, but only to emphasize the need to do a NNC which, after "5 [...] STAB TRIM CUTOUT (both) ...... CUTOUT" only says "6 Stabilizer ...... Trim manually".


I quoted the AD. Wording is probably the same.

I am confused by your argument that the pilots would read enough of the bulletin to know that uncommanded nose down inputs require complying with Runaway Stab NNC, but they don't read the bulletin enough to see the note about using electric trim to reduce control forces?


There's a fundamental difference between reading a bulletin and amending a NNC. Especially since the bulletin (and FAA's AD, which was published 1 day after the bulletin and copies Boeing's wording verbatim) is phrased rather blandly: "...may be..." and "...can be..." hardly convey the idea that electric trim must be used to overcome aerodynamic loads in a full nose-down stab trim configuration while the pilot is pulling up. The Runaway Trim NNC addresses various contingencies (including A/P-induced runaway, and even mechanical failure modes where the trim moves on its own after cutout), but does not say anywhere that stab trim must be returned to neutral with the electric actuator before setting the STAB TRIM CUTOUT switches to cutout.

Since you are confused I will spell it out for you: amending the Runaway Trim NNC would have called for additional sim training, and this was the one thing Boeing would not do.

I am very surprised that members here nitpick on details, but carefully avoid commenting the allegations published in the MarketWatch article (Dow Jones & Co.) quoted in this thread a few posts back:

Throughout the MAX's development, Boeing was intent on minimizing design changes that could require extra pilot training, said Rick Ludtke, a former Boeing engineer who worked on 737 MAXcockpit features but not the MCAS system. Extra training could have added costs for airlines introducing the MAX into service.

The company had promised Southwest Airlines Co., the plane's biggest customer, to keep pilot training to a minimum so the new jet could seamlessly slot into the carrier's fleet of older 737s, according to regulators and industry officials.

Mr. Ludtke recalled midlevel managers telling subordinates that Boeing had committed to pay the airline $1 million per plane if its design ended up requiring pilots to spend additional simulator time. "We had never, ever seen commitments like that before," he said.

Southwest, which has ordered 280 MAX aircraft, declined to comment on the issue, as did Boeing. A Southwest spokeswoman has said the airline developed its 737 MAX training based on Boeing's information and was a recipient of, not a driver of, the training mandates.


Hey, I would have expected some reactions: is this sensationalist drivel? Is Mr. Ludtke a disgruntled ex-employee known to have a bone to pick with Boeing? Is this a politically motivated attack on Boeing? Or should we really consider the possibility that the business case for not amending the Runaway Trim NNC after Lion Air (and for not automatically disabling MCAS on an AoA disagree flag during design, which would have called for additional training as well) was to avoid a 280M$ "penalty" to be paid to SW? That would be a long way past good faith engineering errors and even lack of technical oversight.
 
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SomebodyInTLS
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 12:00 pm

jollo wrote:
Or should we really consider the possibility that the business case for not amending the Runaway Trim NNC after Lion Air (and for not automatically disabling MCAS on an AoA disagree flag during design, which would have called for additional training as well) was to avoid a 280M$ "penalty" to be paid to SW? That would be a long way past good faith engineering errors and even lack of technical oversight.


I was always wondering how exactly the "mistakes" were made in Boeing, and while I assumed it would be something to do with money saving, time pressure and the desire to retain commonality with existing systems and procedures(*) - I found the quotes from that article very enlightening. Seems it was more deliberate than I feared.

(*) Only yesterday I was wondering aloud to a colleague about all this, since he found it incomprehensible that the software depended on a single sensor input, and it occurred to me that the reason for piggy-backing MCAS on the STS system (which uses only one input) could very well be that it is classified as a simple software patch for STS - whereas a "new module" would require additional certification (and possibly lead to the unwanted additional documentation and training).

The fact that STS uses only one sensor is still odd, but not being safety-critical it could get away with it.

Mind you, that does imply that there was deliberate blurring of the lines between safety-critical MCAS and non-critical STS - which does rather tie in with the management behaviour revealed in the article you mentioned.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
PlanesNTrains
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 2:04 pm

jollo wrote:
Cross-posting member rheinwaldner from the B737MAX Grounded Worldwide thread (@Admins: sorry for bending the rules, but this is relevant).

++++++++

Here we have some credible statements, which are not hearsay because the name of the source is known (Rick Ludtke, a former Boeing designer, who worked on the MAXs cockpit interfaces):

Source is the following full copy of the original WSJ article, which is behind a paywall:
https://www.marketwatch.com/press-relea ... quote_news

More from Ludtke here:
https://www.seattletimes.com/business/b ... _inset_1.1

More statements from the following two links:
https://www.satcom.guru/2019/03/regulat ... stems.html
https://www.satcom.guru/2019/03/aoa-van ... g-fix.html


Statement 1: Penalty charges based on training requirements

Mr. Ludtke recalled midlevel managers telling subordinates that Boeing had committed to pay the airline $1 million per plane if its design ended up requiring pilots to spend additional simulator time. "We had never, ever seen commitments like that before," he said.



Statement 2: Pressure to implement no-additional-training solution
"Rick Ludtke, a former Boeing engineer who worked on designing the interfaces on the MAX’s flight deck, said managers mandated that any differences from the previous 737 had to be small enough that they wouldn’t trigger the need for pilots to undergo new simulator training."

"He said that if the group had built the MCAS in a way that would depend on two sensors, and would shut the system off if one fails, he thinks the company would have needed to install an alert in the cockpit to make the pilots aware that the safety system was off. And if that happens, Ludtke said, the pilots would potentially need training on the new alert and the underlying system. That could mean simulator time, which was off the table."


Statement 3: MCAS runaway hard to detect
For the first time, Boeing admits MCAS is an extension of Speed Trim, which I have long suspected, and why it was designed with a single input. Speed Trim is constantly applying stabilizer trim commands in manual flight. This masks MCAS trim commands. Further, MCAS trim commands are effectively a slowover and in the case of the Lion Air flights, intermittent. These factors, combined with the flight deck effects from the high AoA value causing high workload, interfere with the expected human response. There has yet to be any acknowledgement of this, rather the opposite by ignoring it. The FAA repeatedly made the same assertion, the MCAS malfunction is easy to detect.


And

As discussed in earlier posts, in fact MCAS failure is hard to detect as it is a slowover, and Speed Trim System (STS) applies automatic trim routinely, masking MCAS motion. JT043 only related the situation to a stab trim runaway after an observing pilot suggested it. JT610 crew never figured it out. It is possible ET302 flight crew did not detect the failure in spite of specifically be briefed to look for it. The situation was compounded by the AoA trigger of Stall Warning. Boeing should not assume so readily how pilots will perform when MCAS fails, while the evidence is in stark contrast.


Statement 4: After trim cutout, using the trim wheel may be inadequate to deal with the situation
The response to a stabilizer runaway is to cutout the electric trim. Nowhere does anyone caution the consequences of using manual (turn the wheel manually) trim. The manual trim wheel can be very hard to turn if subject to high aero loads, and particularly if the elevator is commanded significantly (loading the stabilizer).


Statement 5: Trim cut out checklist is flawed
The standard response to just hit the stabilizer cutout switches and manually trim is actually flawed. If the nose has been pushed down by significant mistrim (nose down stabilizer, nose up elevator), and as airspeed increases, it may not be possible to trim the stabilizer manually nose up without letting the elevator go to a neutral position. The reality, under the MCAS runaway scenario, trimming nose up immediately stops MCAS as well as trims the stabilizer back towards an in-trim position. At that point, you would be best off to cutout the stabilizer.


30 Pieces of Silver
-Dave


MAX’d out on MAX threads. If you are starting a thread, and it’s about the MAX - stop. There’s already a thread that covers it.
 
many321
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 2:25 pm

jollo wrote:
Cross-posting member rheinwaldner from the B737MAX Grounded Worldwide thread (@Admins: sorry for bending the rules, but this is relevant).

++++++++

Here we have some credible statements, which are not hearsay because the name of the source is known (Rick Ludtke, a former Boeing designer, who worked on the MAXs cockpit interfaces):

Source is the following full copy of the original WSJ article, which is behind a paywall:
https://www.marketwatch.com/press-relea ... quote_news

More from Ludtke here:
https://www.seattletimes.com/business/b ... _inset_1.1

More statements from the following two links:
https://www.satcom.guru/2019/03/regulat ... stems.html
https://www.satcom.guru/2019/03/aoa-van ... g-fix.html


Statement 1: Penalty charges based on training requirements

Mr. Ludtke recalled midlevel managers telling subordinates that Boeing had committed to pay the airline $1 million per plane if its design ended up requiring pilots to spend additional simulator time. "We had never, ever seen commitments like that before," he said.



Statement 2: Pressure to implement no-additional-training solution
"Rick Ludtke, a former Boeing engineer who worked on designing the interfaces on the MAX’s flight deck, said managers mandated that any differences from the previous 737 had to be small enough that they wouldn’t trigger the need for pilots to undergo new simulator training."

"He said that if the group had built the MCAS in a way that would depend on two sensors, and would shut the system off if one fails, he thinks the company would have needed to install an alert in the cockpit to make the pilots aware that the safety system was off. And if that happens, Ludtke said, the pilots would potentially need training on the new alert and the underlying system. That could mean simulator time, which was off the table."


Statement 3: MCAS runaway hard to detect
For the first time, Boeing admits MCAS is an extension of Speed Trim, which I have long suspected, and why it was designed with a single input. Speed Trim is constantly applying stabilizer trim commands in manual flight. This masks MCAS trim commands. Further, MCAS trim commands are effectively a slowover and in the case of the Lion Air flights, intermittent. These factors, combined with the flight deck effects from the high AoA value causing high workload, interfere with the expected human response. There has yet to be any acknowledgement of this, rather the opposite by ignoring it. The FAA repeatedly made the same assertion, the MCAS malfunction is easy to detect.


And

As discussed in earlier posts, in fact MCAS failure is hard to detect as it is a slowover, and Speed Trim System (STS) applies automatic trim routinely, masking MCAS motion. JT043 only related the situation to a stab trim runaway after an observing pilot suggested it. JT610 crew never figured it out. It is possible ET302 flight crew did not detect the failure in spite of specifically be briefed to look for it. The situation was compounded by the AoA trigger of Stall Warning. Boeing should not assume so readily how pilots will perform when MCAS fails, while the evidence is in stark contrast.


Statement 4: After trim cutout, using the trim wheel may be inadequate to deal with the situation
The response to a stabilizer runaway is to cutout the electric trim. Nowhere does anyone caution the consequences of using manual (turn the wheel manually) trim. The manual trim wheel can be very hard to turn if subject to high aero loads, and particularly if the elevator is commanded significantly (loading the stabilizer).


Statement 5: Trim cut out checklist is flawed
The standard response to just hit the stabilizer cutout switches and manually trim is actually flawed. If the nose has been pushed down by significant mistrim (nose down stabilizer, nose up elevator), and as airspeed increases, it may not be possible to trim the stabilizer manually nose up without letting the elevator go to a neutral position. The reality, under the MCAS runaway scenario, trimming nose up immediately stops MCAS as well as trims the stabilizer back towards an in-trim position. At that point, you would be best off to cutout the stabilizer.


Whoa!
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 2:30 pm

jollo wrote:
There's a fundamental difference between reading a bulletin and amending a NNC. Especially since the bulletin (and FAA's AD, which was published 1 day after the bulletin and copies Boeing's wording verbatim) is phrased rather blandly: "...may be..." and "...can be..." hardly convey the idea that electric trim must be used to overcome aerodynamic loads in a full nose-down stab trim configuration while the pilot is pulling up. The Runaway Trim NNC addresses various contingencies (including A/P-induced runaway, and even mechanical failure modes where the trim moves on its own after cutout), but does not say anywhere that stab trim must be returned to neutral with the electric actuator before setting the STAB TRIM CUTOUT switches to cutout.

Since you are confused I will spell it out for you: amending the Runaway Trim NNC would have called for additional sim training, and this was the one thing Boeing would not do.


You didn't address the reason I gave for being confused. The bulletin effectively changes the runaway trim NNC. A pilot would know about the note regarding increased control forces if they read the bulletin. What you are saying is the pilots didn't read the bulletin. Why?
Phrogs Phorever
 
rideforever
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 4:02 pm

AoA vanes operating in the analogue atmosphere will have disagree conditions continuously, so there must be a threshold used to identify sensor malfunctions.
In noticing the failures of triple-AoA arrays on the Airbus, I assume they too have the genius idea of having 3 identical instruments that fail in the same way in the same conditions, rather than 3 different designs with different materials and principles, that do not fail in the same way in the same conditions.
With such breathtaking lack of engineering courage in the industry MCAS is par for the course.
 
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7BOEING7
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 4:30 pm

rideforever wrote:
AoA vanes operating in the analogue atmosphere will have disagree conditions continuously, so there must be a threshold used to identify sensor malfunctions.
In noticing the failures of triple-AoA arrays on the Airbus, I assume they too have the genius idea of having 3 identical instruments that fail in the same way in the same conditions, rather than 3 different designs with different materials and principles, that do not fail in the same way in the same conditions.
With such breathtaking lack of engineering courage in the industry MCAS is par for the course.


Three (or two) different designs require three different certifications and three times as many spares. The MCAS issue aside the extra cost doesn’t bring an equal improvement in safety.
 
jollo
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 4:32 pm

dragon6172 wrote:
jollo wrote:
There's a fundamental difference between reading a bulletin and amending a NNC. Especially since the bulletin (and FAA's AD, which was published 1 day after the bulletin and copies Boeing's wording verbatim) is phrased rather blandly: "...may be..." and "...can be..." hardly convey the idea that electric trim must be used to overcome aerodynamic loads in a full nose-down stab trim configuration while the pilot is pulling up. The Runaway Trim NNC addresses various contingencies (including A/P-induced runaway, and even mechanical failure modes where the trim moves on its own after cutout), but does not say anywhere that stab trim must be returned to neutral with the electric actuator before setting the STAB TRIM CUTOUT switches to cutout.

Since you are confused I will spell it out for you: amending the Runaway Trim NNC would have called for additional sim training, and this was the one thing Boeing would not do.


You didn't address the reason I gave for being confused. The bulletin effectively changes the runaway trim NNC. A pilot would know about the note regarding increased control forces if they read the bulletin. What you are saying is the pilots didn't read the bulletin. Why?


I never said that pilots didn't read the bulletin and associated notes. I'm saying that IMO reading that bulletin does not "effectively" change the checklist. We'll have to agree to disagree.
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 5:15 pm

Heinkel wrote:
These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?

From the UTC flier for the AoA sensor 0861HB certified for Bombardier CRJ /100 /200 /700 and /900:
• Improves reliability
• Decreases maintenance costs
• Reduces flight delays and stall failures
Fleet MTBF greater than 20,000 flight hours
• Easy installation and maintenance
• Form, fit and function interchangeable and intermixable with current AOA
• On-aircraft sensor check using external markings
Self-regulating vane and case heaters with MTBF of greater than 1,000,000 hours (established via field data)
• Low solid-state operating temperature reduces leading edge erosion
• Unique interface between the slinger and faceplate reduces water intrusion
Case heater helps to de-ice external surfaces and evaporate condensation in the unit
• Viscous damper is four times more effective than existing magnetic type which improves output stability and performance during dynamic aircraft maneuvers or crosswind
• Rugged vane construction and low profile reduces ground damage that causes aerodynamic error

With such information, offering one AoA input, two optional for a fee, would seem like a calculated risk.
After all, a/c only have one nose wheel, and they do not seem all that reliable. Why don't they have two?
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 5:56 pm

Backseater wrote:
With such information, offering one AoA input, two optional for a fee, would seem like a calculated risk.

Boeing did not ever offer an option for two AoA inputs to MCAS -- for a fee or for free. There always (unfortunately) was only one, although with the fix there now will be two going forward.

After all, a/c only have one nose wheel, and they do not seem all that reliable. Why don't they have two?

Sorry, but I don't quite follow the logic here. Many airplanes have two nose "wheels." If you're talking about nose gear, one seems for the most part to be pretty reliable.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
Pluto707
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 6:25 pm

An acft that needs software to compensate the deteroriation of aerodynamics should never fly again ! The old 737 wing design is not appropriate for the new and bigger eco engines, there is a point when retrofitting should end, it has been going on for half a century for now...
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 6:51 pm

hivue wrote:
Backseater wrote:
With such information, offering one AoA input, two optional for a fee, would seem like a calculated risk.

Boeing did not ever offer an option for two AoA inputs to MCAS -- for a fee or for free. There always (unfortunately) was only one, although with the fix there now will be two going forward.

After all, a/c only have one nose wheel, and they do not seem all that reliable. Why don't they have two?

Sorry, but I don't quite follow the logic here. Many airplanes have two nose "wheels." If you're talking about nose gear, one seems for the most part to be pretty reliable.

Ok, I stand corrected. The option was that purchased by AA to detect AoA disagreement.
And I meant nose gear. Off the top of my head, an L1011 crashed in the Everglades because the nose gear did not seem to be down and locked. I was looking for important onboard systems that are unique but considered to be reliable enough to be adequate. Like the FDR. Why not two FDRs in two different parts of the middle/aft section. That would give us two pingers with different start time and ping rates (e.g. for MH370 type cases)?
 
luv2cattlecall
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 7:09 pm

Backseater wrote:
Heinkel wrote:
These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?

From the UTC flier for the AoA sensor 0861HB certified for Bombardier CRJ /100 /200 /700 and /900:
• Improves reliability
• Decreases maintenance costs
• Reduces flight delays and stall failures
Fleet MTBF greater than 20,000 flight hours
• Easy installation and maintenance
• Form, fit and function interchangeable and intermixable with current AOA
• On-aircraft sensor check using external markings
Self-regulating vane and case heaters with MTBF of greater than 1,000,000 hours (established via field data)
• Low solid-state operating temperature reduces leading edge erosion
• Unique interface between the slinger and faceplate reduces water intrusion
Case heater helps to de-ice external surfaces and evaporate condensation in the unit
• Viscous damper is four times more effective than existing magnetic type which improves output stability and performance during dynamic aircraft maneuvers or crosswind
• Rugged vane construction and low profile reduces ground damage that causes aerodynamic error

With such information, offering one AoA input, two optional for a fee, would seem like a calculated risk.
After all, a/c only have one nose wheel, and they do not seem all that reliable. Why don't they have two?


What commercial aircraft has only 1 wheel up front?
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 7:33 pm

Backseater wrote:
And I meant nose gear. Off the top of my head, an L1011 crashed in the Everglades because the nose gear did not seem to be down and locked.

The malfunctioning nosegear caused the L1011 to fall out of the sky? Wow. That's news to me.


I was looking for important onboard systems that are unique but considered to be reliable enough to be adequate.

The difference with nose gear is that if it fails, quite often you can still make pretty good job of landing the a/c without too many casualties.

Nothing to see here; move along please.
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 7:34 pm

Backseater wrote:
Off the top of my head, an L1011 crashed in the Everglades because the nose gear did not seem to be down and locked.


EAL 401. The entire flight deck crew was distracted during approach by a faulty nose gear indicator and failed to notice that somebody had accidentally bumped the AP switch and turned off the AP.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
mandala499
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 7:43 pm

Backseater wrote:
I was looking for important onboard systems that are unique but considered to be reliable enough to be adequate.

Try the TAT probe on the Boeings... only one... :)

But then the TAT probe going bonkers doesn't result in the aircraft nosediving though...
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 8:55 pm

Backseater wrote:
PixelFlight wrote:
Is there redundancy for the electronic inside the AoA sensors ?

I doubt it. 2 EEPROMS maybe?
I would write two copies of the configuration and calibration parameters to memory with a hash code, to ensure their validity when the sensor restarts.
And if the microprocessor cannot find a good set, it has no reason to fail high. 0 would prevent MCAS from being triggered.
Of course a constant 0 could never pass the post-install test procedure when it is carried out as required.

Notice also that a microprocessor based AoA with a digital output channel should be very happy to talk to digital avionics. Including outputting the AoA S/N so that it can be written to the FDR. But that connection does not exist today, because it did not exist before!

Multiple redundant values is one thing, but redundant processing is also required for safety critical design.Of course the digital processing allow direct integration into the information network. Someday there will exists AoA sensors that directly provides two redundant AFDX network interfaces.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 8:58 pm

mandala499 wrote:
Try the TAT probe on the Boeings... only one... :)

But then the TAT probe going bonkers doesn't result in the aircraft nosediving though...


I assume Concorde had multiple ways to determine TAT since for that airplane an erroneous value could cause serious problems.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
ikramerica
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 9:19 pm

SheikhDjibouti wrote:
Backseater wrote:
And I meant nose gear. Off the top of my head, an L1011 crashed in the Everglades because the nose gear did not seem to be down and locked.

The malfunctioning nosegear caused the L1011 to fall out of the sky? Wow. That's news to me.


I was looking for important onboard systems that are unique but considered to be reliable enough to be adequate.

The difference with nose gear is that if it fails, quite often you can still make pretty good job of landing the a/c without too many casualties.


Well, there is simply a list of things that can't be made redundant for various reasons.

1. Cockpit
2. Wings
3. Stabs
4. Fuselage
5. Landing Gear

Probably a few others.

But AoA sensors, ADIRUs, etc. need to be redundant.
Of all the things to worry about... the Wookie has no pants.
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 02, 2019 10:03 pm

I apologize for my clumsy examples which I gladly withdraw.
But it looks like there is nothing like a bad post to wake up everybody!

The core of my post was:
From the UTC flier for the AoA sensor 0861HB certified for Bombardier CRJ /100 /200 /700 and /900:
Fleet MTBF greater than 20,000 flight hours

That sensor is not the one installed on the MAX, but from its features and weight, it probably shares the same underlying technology.
So, we have a rather small group of 260 devices with fleet MTBF around 20,000 hours.
Two of them are replaced, each by either a new sensor, or at least one that has been re-certified by a TSO-C54 facility.
Once installed, the test procedure is applied (0, +10, -10, +90, -90... whatever the AMM specifies).
They both pass the test so the units were not DOA.
Each ac is declared serviceable at that point.

Within a few tens of hours, both devices fail soon after take off in a bizarre but probably quite similar manner (fail high), one after 0 flight hour.
What are the possible explanations, assuming the post-install test procedure was completely and successfully performed:
- vane damaged after install (impact by jetway or food truck, being used as a footrest, pressure washer too close,...)
- slightly loose assembly
- ???

At this point, I would pick the slightly loose assembly scenario, as my best guess:
- the installed sensor was actually not new, and it may have been overhauled by some outfit;
- the non-magnetic cage holding the pair of split permanent magnets must be adjustable in rotation with respect to the shaft holding the swept vane to position the magnets vis-a-vis the magnetoresistive sensor;
- let us assume that the screw(s) holding the cage in place were not tightened enough or have lost some of their grips;
- sensor installation calls for positioning the vane at several specific angles with Boeing's test fixture, by hand, meaning gently;
- the tests are successful;
- when the ac accelerates and takes off, the vane is buffeted by the airflow.
- vibrations manage to slightly loosen the cage, inducing an angular offset in the analog signal delivered by the magnetoresistive sensor;
- the analog signal is converted to a digital value that is then transformed according to the calibration table stored in EEPROM.
- as you can see, if the cage slipped just once by a given angle, the final sin & cos offset angle should be close to that value but not constantly so, because of the probable non-linearity of the calibration function.
- and if the final sin & cos offset is a large positive value, we know what happens.
 
maint123
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:14 am

Heinkel wrote:
Backseater wrote:
Are the maintenance records for that aircraft good enough to be released:
- serial numbers of the AoA sensors installed? (by the way, did they find them in the debris? They should have!)
- history records of the AoA sensors (source, repairs, ...)
- detailed records of the installation and test procedure of both sensors on that particular a/c
And if their maintenance records are not good enough, what will they do?


These questions are a red herring. We all know, that AOA-sensors fail from time to time. It is a mechanical moving part, working in harsh environmental conditions.
This is the reason, why essential safety systems of an a/c shouldn't rely on a single AOA-sensor.

The real problem is not, why the sensor failed (they can and they do), the real problem is, that the malfunction of a single AOA-sensor could bring a modern airliner down.

Are there any statistics available, how often AOA-sensors in commercial civial aviation fail worldwide? Daily? Once a week? Once a month? Once a year?

You are not worried that critical sensors in brand new planes are failing after a few months ? Probably nothing wrong physically with the sensors but with the control unit or logic.I fully doubt Boeing has invented new aoa sensors specifically for the max, which no one is able to maintain.
These sort of failures take place after years of operation, or during extreme weather conditions. But new planes are experiencing sensor failures in normal flying conditions and everyone here is mostly concentrating on how the pilots reacted ?
 
Backseater
Posts: 478
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 3:31 am

Well I am worried.
Does anybody know how many AoAs have been replaced among the 70 ac operated by Southwest, American and United?
If any were replaced, what was the disposition of those “faulty” units?
Were they sent back to the manufacturer for analysis?
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 3:44 am

maint123 wrote:
Probably nothing wrong physically with the sensors but with the control unit or logic


But see this quote:
"This means both SMYD and ADIRU/FCC AoA sensed angle were in agreement, subjected to a large bias. This means the AoA sensor output was in error, not any input signal processing."

from this site:
https://www.satcom.guru/2019/03/aoa-van ... g-fix.html

referring to the Lion Air accident flight and the immediately preceding flight.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
djm18
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:02 am

wsj headline...

Ethiopian Airlines Pilots Initially Followed Boeing’s Required Emergency Steps To Disable 737 MAX System
Details of Ethiopian crew’s actions gleaned from preliminary black-box data

https://www.wsj.com/articles/ethiopian- ... eakingnews

from the article...

The se­quence of events, still sub­ject to fur­ther eval­u­a­tion by in­ves­ti­ga­tors, ap­pears to un­der­cut as­ser­tions by Boe­ing and the U.S. Fed­eral Avi­a­tion Ad­min­is­tra­tion over the past five months that by sim­ply fol­low­ing es­tab­lished pro­ce­dures to turn off the sus­pect stall-pre­ven­tion fea­ture, called MCAS, pi­lots could over­come a mis­fire of the sys­tem and avoid end­ing in a crash.

The pi­lots on Ethiopian Air­lines Flight 302 ini­tially re­acted to the emer­gency by shut­ting off power to elec­tric mo­tors dri­ven by the au­to-mated sys­tem, these peo­ple said, but then ap­pear to have re-en­gaged the sys­tem to cope with a per­sis­tent steep nose-down an­gle. It wasn’t im­me­di-ately clear why the pi­lots turned the au­to­mated sys­tem back on in­stead of con­tin­u­ing to fol­low Boe­ing’s stan­dard emer­gency check­list, but gov­ern­ment and in­dus­try of­fi­cials said the likely rea­son would have been be­cause man­ual con­trols to raise the nose didn’t achieve the de­sired re­sults.
Last edited by djm18 on Wed Apr 03, 2019 4:14 am, edited 2 times in total.
 
mzlin
Posts: 123
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:05 am

Okay this is disturbing, WSJ is reporting ET302 pilots DID cut off electrical power to the horizontal stabilizer, tried manual trim, then turned ON the electric trim again, after which they for some reason were not able to counteract errant MCAS-directed downward trim, although that should have been possible with the electrical power back on, using the control column switches: https://www.wsj.com/articles/ethiopian- ... 1554263276

If that is true then the only explanation I can think of is that they (1) didn't think of using, or forgot to use, the electrical trim switches to trim to nose up before cutting the switches, (2) found manual trim too slow to restore neutral or nose-up, and (3) used electrical trim switches to regain nose-up but then didn't continue using them to counteract MCAS.

"The pilots on Ethiopian Airlines Flight 302 initially reacted to the emergency by shutting off power to electric motors driven by the automated system, these people said, but then appear to have re-engaged the system to cope with a persistent steep nose-down angle. It wasn’t immediately clear why the pilots turned the automated system back on instead of continuing to follow Boeing’s standard emergency checklist, but government and industry officials said the likely reason would have been because manual controls to raise the nose didn’t achieve the desired results. After first cranking a manual wheel in the cockpit that controls the same movable surfaces on the plane’s tail that MCAS had affected, the pilots turned electric power back on, one of these people said. They began to use electric switches to try to raise the plane’s nose, according to these people. But the electric power also reactivated MCAS, allowing it to continue its strong downward commands, the people said."

The last two sentences are somewhat contradictory; adjusting electrical trim nose-up should easily counteract MCAS if done properly.

My guess is they did adjust trim nose-up until it was too nose up (recall final recorded vertical speed was high in the positive up direction), but then didn't counteract MCAS as it continued to trim nose-down. This could happen if they were reacting to altitude rather than keeping track of the horizontal stabilizer position. With the aircraft moving upward (after reengaging electrical trim and trimming noseup) the pilots may have felt "safe", even as MCAS trims to full nose-down, because the aircraft will continue moving upward due to momentum even after the trim position reaches negative deflection. That is there is a delay before the nose-down trim produces altitude loss.

This delayed effect is likely to have contributed to FlyDubai and AtlasAir crashes where nose-down trim and nose-down elevator also led to unrecoverable dives from low altitudes (ironically in both cases reaching angles of -49º). Basically by the time the plane starts moving down, there may not be enough time to trim up before the plane hits terrain. Pilots need to proactively level the trim before the plane levels off.
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:38 am

mzlin wrote:
"The pilots on Ethiopian Airlines Flight 302 initially reacted to the emergency by shutting off power to electric motors driven by the automated system, these people said, but then appear to have re-engaged the system to cope with a persistent steep nose-down angle. It wasn’t immediately clear why the pilots turned the automated system back on instead of continuing to follow Boeing’s standard emergency checklist, but government and industry officials said the likely reason would have been because manual controls to raise the nose didn’t achieve the desired results. After first cranking a manual wheel in the cockpit that controls the same movable surfaces on the plane’s tail that MCAS had affected, the pilots turned electric power back on, one of these people said. They began to use electric switches to try to raise the plane’s nose, according to these people. But the electric power also reactivated MCAS, allowing it to continue its strong downward commands, the people said."

My guess it that they could not adjust the trim with the manual wheel due to stabilizer load. Satcom Guru just published a new blog article about this very topic:

A mistrim situation can result if the stabilizer is trimmed nose down and the elevator is commanded nose up. The opposing lift components combine at the jackscrew to create a large upward force, making trimming stabilizer leading edge down difficult. While electric trim motor is designed to not stall out under mistrim conditions, the loads may make trimming by the manual trim wheel very difficult. Under these circumstances, it may be preferable to release the column and let the elevator return to the neutral position, lowering the jackscrew loads and making manual trim easier.

While it's easy to say this during analysis, it's not so easy to remember to do in an emergency situation. Especially since this was probably never covered in any training.

My guess is that since they were not able to trim with the manual wheel, then they re-enabled Electric Trim. Perhaps they got it somewhat leveled out, but now MCAS is kicking in. And if you're under high workload and panic, you could easily lose track of the stabilizer position for a few seconds (especially when they were turning back), and that's all it takes at their AGL to reach an unrecoverable dive.
 
Exeiowa
Posts: 329
Joined: Fri Jul 06, 2018 4:49 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:40 am

Well one thing is for certain these repoers are not good nees for Boeing. At the beginning i thought they would turn this around and after some public humility and hard work everything would work out. As time passes they have looked more dishonest and deliberate in thier actions. Regardless of if they are legally at fault, I think that in the public eye they will be held responsible. Saying this is how rhings are dine etc is not going to cut it.

Manufacturers should strive to make goid systems that minimize risk not ones where they can deploy plausible deniability. Its a sad state of afairs.
 
PacificWest
Posts: 101
Joined: Sun May 06, 2007 3:52 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 6:28 am

flybucky wrote:
mzlin wrote:
"The pilots on Ethiopian Airlines Flight 302 initially reacted to the emergency by shutting off power to electric motors driven by the automated system, these people said, but then appear to have re-engaged the system to cope with a persistent steep nose-down angle. It wasn’t immediately clear why the pilots turned the automated system back on instead of continuing to follow Boeing’s standard emergency checklist, but government and industry officials said the likely reason would have been because manual controls to raise the nose didn’t achieve the desired results. After first cranking a manual wheel in the cockpit that controls the same movable surfaces on the plane’s tail that MCAS had affected, the pilots turned electric power back on, one of these people said. They began to use electric switches to try to raise the plane’s nose, according to these people. But the electric power also reactivated MCAS, allowing it to continue its strong downward commands, the people said."

My guess it that they could not adjust the trim with the manual wheel due to stabilizer load. Satcom Guru just published a new blog article about this very topic:

A mistrim situation can result if the stabilizer is trimmed nose down and the elevator is commanded nose up. The opposing lift components combine at the jackscrew to create a large upward force, making trimming stabilizer leading edge down difficult. While electric trim motor is designed to not stall out under mistrim conditions, the loads may make trimming by the manual trim wheel very difficult. Under these circumstances, it may be preferable to release the column and let the elevator return to the neutral position, lowering the jackscrew loads and making manual trim easier.

While it's easy to say this during analysis, it's not so easy to remember to do in an emergency situation. Especially since this was probably never covered in any training.

My guess is that since they were not able to trim with the manual wheel, then they re-enabled Electric Trim. Perhaps they got it somewhat leveled out, but now MCAS is kicking in. And if you're under high workload and panic, you could easily lose track of the stabilizer position for a few seconds (especially when they were turning back), and that's all it takes at their AGL to reach an unrecoverable dive.



Damn that's kind of a game changer...

Keep in mind the highest these guys got was 1,200 FEET ABOVE GROUND LEVEL

1. MCAS Nose Down at Low Altitude
-- FLIP STAB CUTOUT
-- MANUAL TRIMMING [WHEEL]

2. Pilots feel there's not enough time for Manual Trimming and/or potentially creating High loads from Elevator Nose Up Inputs
-- RELEASE STAB CUTOUT
-- ATTEMPT ELECTRIC TRIMMING [YOKE SWITCHES]
>> MCAS REACTIVATED
 
WIederling
Posts: 9291
Joined: Sun Sep 13, 2015 2:15 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 7:13 am

SomebodyInTLS wrote:
The fact that STS uses only one sensor is still odd, but not being safety-critical it could get away with it.
Mind you, that does imply that there was deliberate blurring of the lines between safety-critical MCAS and non-critical STS - which does rather tie in with the management behaviour revealed in the article you mentioned.


What I still rub with is the combination of a constrictive ( in solution space ) environment
with lots of competing requirements requiring some deep thought
and the general appearance of MCAS and its integration as an interns disinterested make do job.
that reflects a more or less shallow intellectual involvement/process.
Hmm.
Did middle management give direct orders how to do it?
That would fit the competence levels present ( there, in the middle )
Murphy is an optimist
 
WIederling
Posts: 9291
Joined: Sun Sep 13, 2015 2:15 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 7:21 am

PacificWest wrote:
>> MCAS REACTIVATED


The "Proper" strategy to get out of the trap is (now) known.

counter MCAS introduced miss trim with manual switches once in one go and then deactivate trim hard.

This has as a prerogative in knowledge about MCAS<>Trim workings.
Not available at the time.

Will be interesting to see why the ET crew could not fit the information available (what did they really know? Boeing seems to have continued in being stealthy about things.) to them after the Lion Air crash into handling their problems.
Murphy is an optimist

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