kalvado
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Apr 19, 2019 10:01 pm

zeke wrote:
OldAeroGuy wrote:

Careful. ;)


They also suggested to install the camera on a selfie stick as the bird might hit the cage, probe, and skin mounted camera. ;)

They all agreed the last thing that would go through the birds mind was a 737.

I thought last thing going through bird's mind in such a case would be its tail.. That is a critical difference which should totally change certification basis for bird airworthness!
 
PStechPaul
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Apr 19, 2019 11:14 pm

Very funny. But the recent 737MAX crashes have highlighted the potential severity of damaged AoA sensors:

https://canadianbirdstrike.ca/boeings-c ... to-damage/

And my suggestion of bird strike sensors and outside cameras has been proposed elsewhere:

https://www.pprune.org/tech-log/580217- ... -vane.html

The protective cage I suggested seems like it should be effective and cheap to implement. I realize that it could affect the airflow, but not too much if it were just a few pieces of metal or plastic mounted far enough ahead to avoid excessive aerodynamic influence, yet sufficient to deflect (or disintegrate) a bird or similar object.

There is also a swept vane AoA sensor that might be more resistant to damage from FOD, and has a hinged vane so that it will not detach and possibly cause further damage due to engine ingestion or impact on aircraft surfaces.

https://www.safeflight.com/products/aoa ... -vane-aoa/
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 12:25 am

SomebodyInTLS wrote:
I don't doubt that you can estimate AoA through synthesis of a lot of other data - but unless you can measure the local windflow everywhere in the atmosphere at all times it will never be accurate enough to do the job of the AoA vanes.

Of course the AoA vanes are the primary source of the AoA values when there are working perfectly, the issue is how to check that the AoA vanes fit with all others available parameters and how to estimate the AOA value in case the check identify unlikely AoA vanes outputs ? there exists mathematical predictive filters that do both tasks. the accuracy of the estimation will not match the real AoA vanes, but will still be good enough to flight with a reduced flight envelope.
 
hangar30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 12:33 am

Although the 1989 737-400 accident in England was very different, it is at the same time parallel. The pilots, both experienced, were recent converts from the 300 to the 400. There was no simulator conversion, but some of the legacy expectations had changed... The pilots made errors and indeed were faulted for the failure to follow procedures.....but, it is a reminder that experience does not preclude outcomes and that small changes in how an aircraft reacts or performs may end up being significant in emergency or high stress situations...despite the memory items and check lists.
https://en.m.wikipedia.org/wiki/Kegworth_air_disaster

https://assets.publishing.service.gov.u ... G-OBME.pdf
 
smartplane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 3:37 am

zeke wrote:
smartplane wrote:
But the loophole is in the definition of 'change'. As a result of precedent and/or grandfathering, there is provision to accept structural scaling, and material substitution within agreed parameters. And like all precedents, it's been pushed to include flight characteristics, and systems, and............... This is one of the first discussions OEM's have with the authorities when contemplating new models.

Was MCAS a change, or sold as STS enhanced?

Were some changes deemed not to be, on the basis the 737 story would cease with the MAX?


You need to go away and read FAR 21.101. The term change is not a loophole.

MCAS was a change.

Of course it's a loophole.

The OEM (applicant) documents 'changes'.

The applicant highlights 'significant' and 'non-significant' changes.

The applicant's representatives including FAA designated employees, confirm 'significant' changes are significant, and devotes a fraction of the time to confirm 'non-significant' changes are in fact not non-significant, and no time to determine the rest of the aircraft is unchanged.

Significant changes are delegated to the OEM's FAA designated employees for oversight, in turn, audited by the FAA payroll staff, and peer reviewed internally or externally by the FAA.

If MCAS was a change, was it deemed significant? If it was deemed significant, how for example did the change from 0.6 to 2.5 slip through three check processes? Seems more likely it was deemed to be non-significant - STS with a few more bells.
 
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zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 5:37 am

smartplane wrote:
Of course it's a loophole.

The OEM (applicant) documents 'changes'.

The applicant highlights 'significant' and 'non-significant' changes.

The applicant's representatives including FAA designated employees, confirm 'significant' changes are significant, and devotes a fraction of the time to confirm 'non-significant' changes are in fact not non-significant, and no time to determine the rest of the aircraft is unchanged.

Significant changes are delegated to the OEM's FAA designated employees for oversight, in turn, audited by the FAA payroll staff, and peer reviewed internally or externally by the FAA.

If MCAS was a change, was it deemed significant? If it was deemed significant, how for example did the change from 0.6 to 2.5 slip through three check processes? Seems more likely it was deemed to be non-significant - STS with a few more bells.


It is not a loophole, otherwise you could point to the FAR which supports your statements.

All the changes would be fully documented in the design, production, certification documents, new part numbers for hardware and software, maintenance manuals, and pilot training.

To be clear the original MCAS implementation was not dangerous if the sensors were working, it is only after a AOA failure case, and again after the crew failed to perform mandatory procedure (unreliable airspeed) that this MCAS issue raised its head. MCAS should be as invisible to the crew as a yaw dampener.

To me the engineering fix is easy, what worries me is the human factors issues as to why multiple crews did not perform their required procedures.

To be further clear, MCAS did not operate with flaps down, why didn’t the pilots deal with the stick shaker immediately?
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
Interested
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 5:54 am

It's in the news today that 3 agencies, 8 countries plus Europe are together reviewing how the Max 737 was ever certified safe to fly in the first place
 
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zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 5:58 am

Interested wrote:
It's in the news today that 3 agencies, 8 countries plus Europe are together reviewing how the Max 737 was ever certified safe to fly in the first place


It isn’t actually news, the Joint Authorities Technical Review (JATR) for Boeing 737 MAX was announced by the FAA in early February.

https://www.faa.gov/news/updates/?newsId=93206
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 7:37 am

zeke wrote:
smartplane wrote:
Of course it's a loophole.

The OEM (applicant) documents 'changes'.

The applicant highlights 'significant' and 'non-significant' changes.

The applicant's representatives including FAA designated employees, confirm 'significant' changes are significant, and devotes a fraction of the time to confirm 'non-significant' changes are in fact not non-significant, and no time to determine the rest of the aircraft is unchanged.

Significant changes are delegated to the OEM's FAA designated employees for oversight, in turn, audited by the FAA payroll staff, and peer reviewed internally or externally by the FAA.

If MCAS was a change, was it deemed significant? If it was deemed significant, how for example did the change from 0.6 to 2.5 slip through three check processes? Seems more likely it was deemed to be non-significant - STS with a few more bells.


It is not a loophole, otherwise you could point to the FAR which supports your statements.

All the changes would be fully documented in the design, production, certification documents, new part numbers for hardware and software, maintenance manuals, and pilot training.

To be clear the original MCAS implementation was not dangerous if the sensors were working, it is only after a AOA failure case, and again after the crew failed to perform mandatory procedure (unreliable airspeed) that this MCAS issue raised its head. MCAS should be as invisible to the crew as a yaw dampener.

To me the engineering fix is easy, what worries me is the human factors issues as to why multiple crews did not perform their required procedures.

To be further clear, MCAS did not operate with flaps down, why didn’t the pilots deal with the stick shaker immediately?


Wether there is some differentiation between a significant or not-significnat change or not, the point is that the system was classified 'Hazardous' (stated in these threads) and is a modification to the FCC and so should have been held to the same standards as FCC and Hazardous classification.

Ray
 
flybucky
Posts: 175
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 7:37 am

Mentour Pilot's latest youtube video: "Boeing 737 Unable to Trim!! Cockpit video (Full flight sim)". It seems to include some clips from the deleted video:
https://www.youtube.com/watch?v=aoNOVlxJmow
 
Interested
Posts: 647
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 8:57 am

zeke wrote:
Interested wrote:
It's in the news today that 3 agencies, 8 countries plus Europe are together reviewing how the Max 737 was ever certified safe to fly in the first place


It isn’t actually news, the Joint Authorities Technical Review (JATR) for Boeing 737 MAX was announced by the FAA in early February.

https://www.faa.gov/news/updates/?newsId=93206



It is news as it confirms the countries and agencies that are part of the review and the start date which is 29th April. They also state that they anticipate the review will take 3 months approx.

Taking us to the end of July

So I can't see these planes flying again til then at the earliest. And then whether they fly will be subject to the findings of the review regardless
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 12:12 pm

smartplane wrote:
PixelFlight wrote:
zeke wrote:
MCAS from what I understand is designed to operate at high angles of bank and high air speeds. I would not be confident in guessing my AOA in such an attitude. This is common to both JT and ET crashes, both were in high angle of bank turns just prior to crashing.

The high bank angle is probably a consequence of the final lost of control. I doubt that the JT and ET pilots that was on high workload fighting to save the aircraft would voluntary command a such attitude.

Or like in many vehicle stability control systems, even when supposedly powered off, in certain 'threatening' situations, can re-start for the duration of the threat? In high angles of bank, does MCAS re-start, even if the switches say no?

MCAS is specific to the B737 MAX, and if any of the 2 stab trim cutoff switches is in the "cutoff" position, the electric horizontal stabilized trim motor is not powered anymore. So it that case "if the switches say no", even if the FCC generate a MCAS command there is no electric power to physically move the horizontal stabilized. The only remaining action to move the horizontal stabilized is the manual trim wheels, but it's nearly impossible to use them at high airspeed. In conclusion: stab trim cutoff in "cutoff" + high airspeed = horizontal stabilized.stuck in place. The last remaining relevant control surface are the horizontal elevators, but with much lower surface area than the horizontal stabilizer the pilot can't overcome an extreme horizontal stabilizer position. Final conclusion: stab trim cutoff in "cutoff" + high airspeed + horizontal stabilized in extreme position = crash. The major issue with an AoA fault on a B737 MAX is that 1) The MCAS put the stabilized in extreme position 2) The MCAS action force the pilot to move the stab trim cutoff in "cutoff" 3) The AoA fault produce an airspeed disagree (due to correction algorithm) confusing the pilot about airspeed. Recipe for a disaster.
 
yurieu
Posts: 2
Joined: Thu Mar 14, 2019 2:07 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 1:53 pm

morrisond wrote:
yurieu wrote:
morrisond wrote:


Yes they did - it was a real screw up. It sounds like MCAS v2 will do exactly what it was supposed to do the first time. It is a feel system not a stall prevention system - the MAX won't fall out of the sky without it.

It would have been better off without it.

It is impossible due to the new engine forward positioned.The plane needs the software to be able to fly and anything unnexpected can result in software error and falling down. What can they do? It's something to think during a reunion, in a building, or on a prototype model, but the plane is already approved to general use and has a unforggivable death toll.


No it doesn't need software to fly. It is able to flown in full manual control without any electronic intervention. The more forward COG of the engines would actually help it in some instances. In any case the change in COG will be no more than than first 5-6 rows of the aircraft being full or half full - and maybe not even that much.

It’s able to fly in full manual, but what about software pointing down, too heavy stick to pull on manual?

And this can’t go on unpunished, aviation can’t have a precedent for hidden software in new planes.
 
XRAYretired
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Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 3:29 pm

A consensus seems to be building that the incorrect AOA signal is the result of an ADIRU problem rather than AOA sensor problem not least because (as I was forcibly advised) AOA high signal, when processed with Pitot tube signal to calculate IAS would result in IAS higher on the affected side than the other. Whereas, the FDR presented, whilst indicating IAS to be disagreeing between sides is actually low on the affected side (left).

So, this dumb sap thought he'd have a go at making sense of the data we have in this light. Firstly, the FDR AOA signal can be reasonably deduced to be as out-put from the ADIRU, since we know it caused the MCAS activation, and therefore, we can reasonable assume the IAS and Altitude FDR signals are also as out-put from the ADIRU (irrespective of the point they are actually sampled). So, the signals are all post ADIRU processing.

I can find no further detail on how the signals are processed within the ADIRU, other than that AOA is received as analogue and converted to digital prior to processor (could just be dumb sap syndrome).

The FDR shows AOA, IAS and Altitude signals (left) all deviating from the same time stamp and consistently until ~20 secs from the end of the recording. So, are we looking for some common factor in signal processing that affects AOA massively high and IAS and Altitude ~10% low. Do we know what this could be?

During the last ~20 seconds of the record, all three signals (left) vary to coincidence with the right hand signals not seemingly consistent with the pitch, but much so the acceleration. Are all three signals modified By the Inertial Reference module?
Could this consistent with Preliminary Report statement - 'Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.'-

In comparison with the Lion Air event, there seems to be correlation AOA high, IAS low (Altitude NK). Is this event also initiated by an ADIRU problem?, if so, it must be subtly different in that AOA appears consistently ~20deg. High (not up at 74deg).

Abusive or other responses equally anticipated.

Ray
 
fadecfault
Posts: 164
Joined: Mon Nov 05, 2007 8:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 8:35 pm

XRAYretired wrote:
A consensus seems to be building that the incorrect AOA signal is the result of an ADIRU problem rather than AOA sensor problem not least because (as I was forcibly advised) AOA high signal, when processed with Pitot tube signal to calculate IAS would result in IAS higher on the affected side than the other. Whereas, the FDR presented, whilst indicating IAS to be disagreeing between sides is actually low on the affected side (left).

So, this dumb sap thought he'd have a go at making sense of the data we have in this light. Firstly, the FDR AOA signal can be reasonably deduced to be as out-put from the ADIRU, since we know it caused the MCAS activation, and therefore, we can reasonable assume the IAS and Altitude FDR signals are also as out-put from the ADIRU (irrespective of the point they are actually sampled). So, the signals are all post ADIRU processing.

I can find no further detail on how the signals are processed within the ADIRU, other than that AOA is received as analogue and converted to digital prior to processor (could just be dumb sap syndrome).

The FDR shows AOA, IAS and Altitude signals (left) all deviating from the same time stamp and consistently until ~20 secs from the end of the recording. So, are we looking for some common factor in signal processing that affects AOA massively high and IAS and Altitude ~10% low. Do we know what this could be?

During the last ~20 seconds of the record, all three signals (left) vary to coincidence with the right hand signals not seemingly consistent with the pitch, but much so the acceleration. Are all three signals modified By the Inertial Reference module?
Could this consistent with Preliminary Report statement - 'Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.'-

In comparison with the Lion Air event, there seems to be correlation AOA high, IAS low (Altitude NK). Is this event also initiated by an ADIRU problem?, if so, it must be subtly different in that AOA appears consistently ~20deg. High (not up at 74deg).

Abusive or other responses equally anticipated.

Ray

If you want to blame the adiru you need to explain why the stick shaker was operating. Everyone here who wants to blame the adiru seem to gloss over that very important fact.
The views and opinions written here are my own and do not reflect those of my employer.
 
XRAYretired
Posts: 626
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 8:58 pm

fadecfault wrote:
XRAYretired wrote:
A consensus seems to be building that the incorrect AOA signal is the result of an ADIRU problem rather than AOA sensor problem not least because (as I was forcibly advised) AOA high signal, when processed with Pitot tube signal to calculate IAS would result in IAS higher on the affected side than the other. Whereas, the FDR presented, whilst indicating IAS to be disagreeing between sides is actually low on the affected side (left).

So, this dumb sap thought he'd have a go at making sense of the data we have in this light. Firstly, the FDR AOA signal can be reasonably deduced to be as out-put from the ADIRU, since we know it caused the MCAS activation, and therefore, we can reasonable assume the IAS and Altitude FDR signals are also as out-put from the ADIRU (irrespective of the point they are actually sampled). So, the signals are all post ADIRU processing.

I can find no further detail on how the signals are processed within the ADIRU, other than that AOA is received as analogue and converted to digital prior to processor (could just be dumb sap syndrome).

The FDR shows AOA, IAS and Altitude signals (left) all deviating from the same time stamp and consistently until ~20 secs from the end of the recording. So, are we looking for some common factor in signal processing that affects AOA massively high and IAS and Altitude ~10% low. Do we know what this could be?

During the last ~20 seconds of the record, all three signals (left) vary to coincidence with the right hand signals not seemingly consistent with the pitch, but much so the acceleration. Are all three signals modified By the Inertial Reference module?
Could this consistent with Preliminary Report statement - 'Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.'-

In comparison with the Lion Air event, there seems to be correlation AOA high, IAS low (Altitude NK). Is this event also initiated by an ADIRU problem?, if so, it must be subtly different in that AOA appears consistently ~20deg. High (not up at 74deg).

Abusive or other responses equally anticipated.

Ray

If you want to blame the adiru you need to explain why the stick shaker was operating. Everyone here who wants to blame the adiru seem to gloss over that very important fact.


Actually, I thought it was AOA. But have been chewed out by another poster and AvH seem to believe its ADIRU as well, so this is my attempt to explore this option. So I throw it back, does AOA high not trigger the stick shaker? If not what does?

Ray
 
smartplane
Posts: 1024
Joined: Fri Aug 03, 2018 9:23 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 8:58 pm

PixelFlight wrote:
smartplane wrote:
Or like in many vehicle stability control systems, even when supposedly powered off, in certain 'threatening' situations, can re-start for the duration of the threat? In high angles of bank, does MCAS re-start, even if the switches say no?

MCAS is specific to the B737 MAX, and if any of the 2 stab trim cutoff switches is in the "cutoff" position, the electric horizontal stabilized trim motor is not powered anymore. So it that case "if the switches say no", even if the FCC generate a MCAS command there is no electric power to physically move the horizontal stabilized. The only remaining action to move the horizontal stabilized is the manual trim wheels, but it's nearly impossible to use them at high airspeed. In conclusion: stab trim cutoff in "cutoff" + high airspeed = horizontal stabilized.stuck in place. The last remaining relevant control surface are the horizontal elevators, but with much lower surface area than the horizontal stabilizer the pilot can't overcome an extreme horizontal stabilizer position. Final conclusion: stab trim cutoff in "cutoff" + high airspeed + horizontal stabilized in extreme position = crash. The major issue with an AoA fault on a B737 MAX is that 1) The MCAS put the stabilized in extreme position 2) The MCAS action force the pilot to move the stab trim cutoff in "cutoff" 3) The AoA fault produce an airspeed disagree (due to correction algorithm) confusing the pilot about airspeed. Recipe for a disaster.

Many thanks for the comprehensive explanation.
Isn't MCAS also installed in some military 767's?
Can / does MCAS 'save' commands, so when stab trim switches powered on, it immediately takes effect?
 
sgrow787
Posts: 262
Joined: Fri May 16, 2014 8:12 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 20, 2019 9:46 pm

fadecfault wrote:
If you want to blame the adiru you need to explain why the stick shaker was operating. Everyone here who wants to blame the adiru seem to gloss over that very important fact.


Simple. As evident in the block diagram on page 17 of the ET302 preliminary report - and the same diagram presented by experienced pilot and youtuber "blancolirio" - the SMYD for the 737 Max has it's AOA data source coming from the ADIRU, not the AOA sensor itself. This explains why, on page 27 of the report, stick shaker turns off during the good-value blips at 05:43:27 and 05:43:37 (good values indicated by L/R values overlapping on top of each other).

For the Lion Air JT610 crash, looking at page 14 of the JT610 preliminary report, there were no good-value blips in the output of the ADIRU. So the stick shaker was on the entire flight (with the exception at 23:22:45 due to the simultaneous peak in airspeed).

As for the SMYD being absorbed into the FCC on the Max, this seems to be supported by no SMYD LRU being listed in the 737 Max MMEL, as stated by Satcom Guru:

https://www.satcom.guru/2019/03/taking- ... ng-on.html

"I can find no entry for the SMYD in the 737 MAX Master Minimum Equipment List (MMEL). It is provided clearly in the prior 737 (NG) MMEL. This, in combination with the above, leads me to wonder if the SMYD is still an LRU on the 737 MAX, or did it get absorbed as a function into another LRU?"
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
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PixelFlight
Posts: 648
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 12:47 am

smartplane wrote:
Many thanks for the comprehensive explanation.
Isn't MCAS also installed in some military 767's?
Can / does MCAS 'save' commands, so when stab trim switches powered on, it immediately takes effect?

Yes the military 767 seem to have the MCAS.
From an engineer point of view I d'on't see any argument to save a command to take effect alter on an aircraft. The aircraft attitude could change quickly, making previous command obsolete. But if the conditions for MCAS activation are true when the stab trim cutoff switches are back to normal, then is will immediately generate a command.
 
fadecfault
Posts: 164
Joined: Mon Nov 05, 2007 8:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 2:57 am

XRAYretired wrote:
fadecfault wrote:
XRAYretired wrote:
A consensus seems to be building that the incorrect AOA signal is the result of an ADIRU problem rather than AOA sensor problem not least because (as I was forcibly advised) AOA high signal, when processed with Pitot tube signal to calculate IAS would result in IAS higher on the affected side than the other. Whereas, the FDR presented, whilst indicating IAS to be disagreeing between sides is actually low on the affected side (left).

So, this dumb sap thought he'd have a go at making sense of the data we have in this light. Firstly, the FDR AOA signal can be reasonably deduced to be as out-put from the ADIRU, since we know it caused the MCAS activation, and therefore, we can reasonable assume the IAS and Altitude FDR signals are also as out-put from the ADIRU (irrespective of the point they are actually sampled). So, the signals are all post ADIRU processing.

I can find no further detail on how the signals are processed within the ADIRU, other than that AOA is received as analogue and converted to digital prior to processor (could just be dumb sap syndrome).

The FDR shows AOA, IAS and Altitude signals (left) all deviating from the same time stamp and consistently until ~20 secs from the end of the recording. So, are we looking for some common factor in signal processing that affects AOA massively high and IAS and Altitude ~10% low. Do we know what this could be?

During the last ~20 seconds of the record, all three signals (left) vary to coincidence with the right hand signals not seemingly consistent with the pitch, but much so the acceleration. Are all three signals modified By the Inertial Reference module?
Could this consistent with Preliminary Report statement - 'Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.'-

In comparison with the Lion Air event, there seems to be correlation AOA high, IAS low (Altitude NK). Is this event also initiated by an ADIRU problem?, if so, it must be subtly different in that AOA appears consistently ~20deg. High (not up at 74deg).

Abusive or other responses equally anticipated.

Ray

If you want to blame the adiru you need to explain why the stick shaker was operating. Everyone here who wants to blame the adiru seem to gloss over that very important fact.


Actually, I thought it was AOA. But have been chewed out by another poster and AvH seem to believe its ADIRU as well, so this is my attempt to explore this option. So I throw it back, does AOA high not trigger the stick shaker? If not what does?

Ray

Yes high aoa does trigger the stick shaker based on airspeed. The stick shaker is operated by the symd with a direct input from channel "a" of the aoa. It only gets airspeed data from the adiru, not aoa. Channel "b" goes to the adiru.

Each "channel" on the aoa is feed by two different power sources. One output channel goes to the symd to operate the stick shaker and elevator feel module. The other goes to the adiru and down line to the FCC.
The views and opinions written here are my own and do not reflect those of my employer.
 
planecane
Posts: 1142
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 3:16 am

PixelFlight wrote:
smartplane wrote:
PixelFlight wrote:
The high bank angle is probably a consequence of the final lost of control. I doubt that the JT and ET pilots that was on high workload fighting to save the aircraft would voluntary command a such attitude.

Or like in many vehicle stability control systems, even when supposedly powered off, in certain 'threatening' situations, can re-start for the duration of the threat? In high angles of bank, does MCAS re-start, even if the switches say no?

MCAS is specific to the B737 MAX, and if any of the 2 stab trim cutoff switches is in the "cutoff" position, the electric horizontal stabilized trim motor is not powered anymore. So it that case "if the switches say no", even if the FCC generate a MCAS command there is no electric power to physically move the horizontal stabilized. The only remaining action to move the horizontal stabilized is the manual trim wheels, but it's nearly impossible to use them at high airspeed. In conclusion: stab trim cutoff in "cutoff" + high airspeed = horizontal stabilized.stuck in place. The last remaining relevant control surface are the horizontal elevators, but with much lower surface area than the horizontal stabilizer the pilot can't overcome an extreme horizontal stabilizer position. Final conclusion: stab trim cutoff in "cutoff" + high airspeed + horizontal stabilized in extreme position = crash. The major issue with an AoA fault on a B737 MAX is that 1) The MCAS put the stabilized in extreme position 2) The MCAS action force the pilot to move the stab trim cutoff in "cutoff" 3) The AoA fault produce an airspeed disagree (due to correction algorithm) confusing the pilot about airspeed. Recipe for a disaster.

Your narrative is great except that the manual trim wheel should not come into play when recovering from an MCAS runaway. The runaway stabilizer procedure says to use manual electric trim to balance the control forces before moving the switches to cutout. The manual trim wheel should only be needed once the aircraft is in trim where it will be usable.
 
fadecfault
Posts: 164
Joined: Mon Nov 05, 2007 8:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 3:23 am

sgrow787 wrote:
fadecfault wrote:
If you want to blame the adiru you need to explain why the stick shaker was operating. Everyone here who wants to blame the adiru seem to gloss over that very important fact.


Simple. As evident in the block diagram on page 17 of the ET302 preliminary report - and the same diagram presented by experienced pilot and youtuber "blancolirio" - the SMYD for the 737 Max has it's AOA data source coming from the ADIRU, not the AOA sensor itself. This explains why, on page 27 of the report, stick shaker turns off during the good-value blips at 05:43:27 and 05:43:37 (good values indicated by L/R values overlapping on top of each other).

For the Lion Air JT610 crash, looking at page 14 of the JT610 preliminary report, there were no good-value blips in the output of the ADIRU. So the stick shaker was on the entire flight (with the exception at 23:22:45 due to the simultaneous peak in airspeed).

As for the SMYD being absorbed into the FCC on the Max, this seems to be supported by no SMYD LRU being listed in the 737 Max MMEL, as stated by Satcom Guru:

https://www.satcom.guru/2019/03/taking- ... ng-on.html

"I can find no entry for the SMYD in the 737 MAX Master Minimum Equipment List (MMEL). It is provided clearly in the prior 737 (NG) MMEL. This, in combination with the above, leads me to wonder if the SMYD is still an LRU on the 737 MAX, or did it get absorbed as a function into another LRU?"

No the symds are not intergrated with the fccs. No it does not get aoa from the adiru.

This is what happens when you have bad information.
The views and opinions written here are my own and do not reflect those of my employer.
 
sgrow787
Posts: 262
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 4:44 am

fadecfault wrote:
No the symds are not intergrated with the fccs. No it does not get aoa from the adiru.

This is what happens when you have bad information.


Well what is YOUR source?
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
PlanesNTrains
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 4:55 am

I’m looking forward to the final report as it’s hard to keep all the contradicting “facts” in this thread straight.
-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.
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 6:56 am

planecane wrote:
Your narrative is great except that the manual trim wheel should not come into play when recovering from an MCAS runaway. The runaway stabilizer procedure says to use manual electric trim to balance the control forces before moving the switches to cutout. The manual trim wheel should only be needed once the aircraft is in trim where it will be usable.

The runaway stabilizer procedure does not explicitly say that Electric Trim should be used to balance the control forces before moving the switches to cutout. Step 2 (if Autopilot is engaged) does mention the electric trim, but that is only if Autopilot is engaged, which it is not the case during MCAS. Step 5 says to move both Stab Trim Cutout switches to Cutout, but no mention of using Electric Trim before doing so.

Even the TBC-19 bulletin (issued after Lion Air JT610) does not explicitly say to use Electric Trim before Stab Trim Cutout. It says:

"In the event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9... do the Runaway Stabilizer NNC ensuring that the Stab Trim Cutout switches are set to Cutout... Note: 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 after the Stab Trim Cutout switches are moved to Cutout."

It only suggests that Electric Trim can be used, not that it must be used before Cutout. It explicitly says that manual wheel trim can be used after Stab Trim Cutout.
 
Etheereal
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 7:38 am

PlanesNTrains wrote:
I’m looking forward to the final report as it’s hard to keep all the contradicting “facts” in this thread straight.

There will be people that will dismiss the final report because it doesnt fit their headcannon.
JetBuddy wrote:
"737 slides off the runway" is the new "Florida man"..

:lol:
 
JibberJim
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 7:40 am

flybucky wrote:
Even the TBC-19 bulletin (issued after Lion Air JT610) does not explicitly say to use Electric Trim before Stab Trim Cutout. It says:


Well presumably it can't possibly do that, in a failure mode where the trim is running away and the electrical buttons do nothing (ie broken switches) then using electric trim before would be impossible. So the little "note", certainly seems to be an attempt to give required information, but without changing the memory procedure or adding a new one.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 9:02 am

JibberJim wrote:
flybucky wrote:
Even the TBC-19 bulletin (issued after Lion Air JT610) does not explicitly say to use Electric Trim before Stab Trim Cutout. It says:


Well presumably it can't possibly do that, in a failure mode where the trim is running away and the electrical buttons do nothing (ie broken switches) then using electric trim before would be impossible. So the little "note", certainly seems to be an attempt to give required information, but without changing the memory procedure or adding a new one.

The fact of the matter is the EAD failed to save the A/C on the one occasion it was needed. You are suggesting that the EAD would either have to be insufficiently simple or overly complex. It looks very much like they gambled on insufficiently simple and that a fix would be in before the next occurrence. 150+ people lost.

Ray
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 3:48 pm

flybucky wrote:
planecane wrote:
Your narrative is great except that the manual trim wheel should not come into play when recovering from an MCAS runaway. The runaway stabilizer procedure says to use manual electric trim to balance the control forces before moving the switches to cutout. The manual trim wheel should only be needed once the aircraft is in trim where it will be usable.

The runaway stabilizer procedure does not explicitly say that Electric Trim should be used to balance the control forces before moving the switches to cutout. Step 2 (if Autopilot is engaged) does mention the electric trim, but that is only if Autopilot is engaged, which it is not the case during MCAS. Step 5 says to move both Stab Trim Cutout switches to Cutout, but no mention of using Electric Trim before doing so.

Even the TBC-19 bulletin (issued after Lion Air JT610) does not explicitly say to use Electric Trim before Stab Trim Cutout. It says:

"In the event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9... do the Runaway Stabilizer NNC ensuring that the Stab Trim Cutout switches are set to Cutout... Note: 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 after the Stab Trim Cutout switches are moved to Cutout."

It only suggests that Electric Trim can be used, not that it must be used before Cutout. It explicitly says that manual wheel trim can be used after Stab Trim Cutout.

Many thanks "flybucky" for your detailed clarification.

My narrative was factual on the conditions that are know to be required for a specific consequence. If any of the conditions is not true (for whatever reason), then the consequence can't apply the same way. There are many hot debate about the exact procedure the pilots should follow to survive an AoA fault event on a 737 MAX MCAS v1. From the JT610 and ET302 very factual crashes and various simulator sessions, it pretty clear that this is a very dangerous situation and that the published procedure is not addressing correctly the severity of that situation. The only fact that there are more than a single interpretation of the published procedure show very well the basic issue of transmitting exactly an important procedure from a human brain to a other human brain,
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 4:10 pm

PixelFlight wrote:
flybucky wrote:
planecane wrote:
Your narrative is great except that the manual trim wheel should not come into play when recovering from an MCAS runaway. The runaway stabilizer procedure says to use manual electric trim to balance the control forces before moving the switches to cutout. The manual trim wheel should only be needed once the aircraft is in trim where it will be usable.

The runaway stabilizer procedure does not explicitly say that Electric Trim should be used to balance the control forces before moving the switches to cutout. Step 2 (if Autopilot is engaged) does mention the electric trim, but that is only if Autopilot is engaged, which it is not the case during MCAS. Step 5 says to move both Stab Trim Cutout switches to Cutout, but no mention of using Electric Trim before doing so.

Even the TBC-19 bulletin (issued after Lion Air JT610) does not explicitly say to use Electric Trim before Stab Trim Cutout. It says:

"In the event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9... do the Runaway Stabilizer NNC ensuring that the Stab Trim Cutout switches are set to Cutout... Note: 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 after the Stab Trim Cutout switches are moved to Cutout."

It only suggests that Electric Trim can be used, not that it must be used before Cutout. It explicitly says that manual wheel trim can be used after Stab Trim Cutout.

Many thanks "flybucky" for your detailed clarification.

My narrative was factual on the conditions that are know to be required for a specific consequence. If any of the conditions is not true (for whatever reason), then the consequence can't apply the same way. There are many hot debate about the exact procedure the pilots should follow to survive an AoA fault event on a 737 MAX MCAS v1. From the JT610 and ET302 very factual crashes and various simulator sessions, it pretty clear that this is a very dangerous situation and that the published procedure is not addressing correctly the severity of that situation. The only fact that there are more than a single interpretation of the published procedure show very well the basic issue of transmitting exactly an important procedure from a human brain to a other human brain,


I guess you didn't read my earlier reply. The word "Note:" does not appear before the statement you quoted. Those two sentences are not describing the procedure. They are informing the pilots what type of trim is available depending on the position of the Stab Trim Cutout switches. It is not suggesting anything. It is describing the function of the switches so that after moving them to cutout, the pilots know that the manual electric trim will not do anything.

This narrative that using electric trim to get the aircraft back into trim is some kind of glossed over footnote is simply not correct. The second step in the procedure after "disengage autopilot" is "control airplane pitch attitude with control column and main electric trim as required." This is the first sentence of the "Runaway Stabilizer procedure above" that they are instructed to perform in the "event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9."

It is not a suggestion. It explicitly says to use the main electric trim. I don't know how much more clear it could be. Did they need to state "press the thumb switch on the yoke up until the aircraft is back in trim and then remove your finger." I would hope that anybody that is certified to fly an aircraft and has passed the necessary tests has the reading comprehension to understand the procedure.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 6:37 pm

planecane wrote:
I guess you didn't read my earlier reply. The word "Note:" does not appear before the statement you quoted. Those two sentences are not describing the procedure. They are informing the pilots what type of trim is available depending on the position of the Stab Trim Cutout switches. It is not suggesting anything. It is describing the function of the switches so that after moving them to cutout, the pilots know that the manual electric trim will not do anything.

This narrative that using electric trim to get the aircraft back into trim is some kind of glossed over footnote is simply not correct. The second step in the procedure after "disengage autopilot" is "control airplane pitch attitude with control column and main electric trim as required." This is the first sentence of the "Runaway Stabilizer procedure above" that they are instructed to perform in the "event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9."

It is not a suggestion. It explicitly says to use the main electric trim. I don't know how much more clear it could be. Did they need to state "press the thumb switch on the yoke up until the aircraft is back in trim and then remove your finger." I would hope that anybody that is certified to fly an aircraft and has passed the necessary tests has the reading comprehension to understand the procedure.

Sorry but the word "Note: " is really prefixing the stab trim neutralization paragraph, even the indentation emphasis that fact:
Image

I hope you noticed that it's not so clear for everybody and every pilots, and this is the main problem. Even the name of the procedure is debated, because it's really an AoA fault and not a runaway stab trim. I think that even the EAD procedure is flawed because the procedure did not clearly explain to the pilot that there have only a few seconds after the last manual electric trim to move the stab trim cutoff switch to "cutoff" before the MCAS will again trim quickly the stab in an extreme position.
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 8:10 pm

PixelFlight wrote:
planecane wrote:
I guess you didn't read my earlier reply. The word "Note:" does not appear before the statement you quoted. Those two sentences are not describing the procedure. They are informing the pilots what type of trim is available depending on the position of the Stab Trim Cutout switches. It is not suggesting anything. It is describing the function of the switches so that after moving them to cutout, the pilots know that the manual electric trim will not do anything.

This narrative that using electric trim to get the aircraft back into trim is some kind of glossed over footnote is simply not correct. The second step in the procedure after "disengage autopilot" is "control airplane pitch attitude with control column and main electric trim as required." This is the first sentence of the "Runaway Stabilizer procedure above" that they are instructed to perform in the "event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9."

It is not a suggestion. It explicitly says to use the main electric trim. I don't know how much more clear it could be. Did they need to state "press the thumb switch on the yoke up until the aircraft is back in trim and then remove your finger." I would hope that anybody that is certified to fly an aircraft and has passed the necessary tests has the reading comprehension to understand the procedure.

Sorry but the word "Note: " is really prefixing the stab trim neutralization paragraph, even the indentation emphasis that fact:
Image

I hope you noticed that it's not so clear for everybody and every pilots, and this is the main problem. Even the name of the procedure is debated, because it's really an AoA fault and not a runaway stab trim. I think that even the EAD procedure is flawed because the procedure did not clearly explain to the pilot that there have only a few seconds after the last manual electric trim to move the stab trim cutoff switch to "cutoff" before the MCAS will again trim quickly the stab in an extreme position.


I don't know what document that is an image of but the following is a link to the EAD residing on the FAA website. It does not look the same as what you posted (aside from the fact that you didn't include the actual procedure part of the document anyway). http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 8:46 pm

planecane wrote:
It is not a suggestion. It explicitly says to use the main electric trim. I don't know how much more clear it could be.

It may be clear to you and others, but it could definitely could have been written to be more clear. ET302 did use Electric Trim before Stab Trim Cutout. They just didn't use it enough. Here's a breakdown of the first paragraph of the EAD as it applied to ET302:

"Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required."

ET302 did disengage AP. And they did control the pitch attitude with a combination of the control column and main electric trim. They were able to hold the Pitch Attitude between 0 to 5º.

"If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT."

Relaxing the column was causing the trim to move, so they set the Stab Trim to Cutout.

If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually.

From the best we can tell from the FDR and CVR, ET302 did attempt to trim the plane manually with the trim wheel, unsuccessfully.

If the EAD were written this way, it would have been explicitly clear with no room for misinterpretation (my edits in BOLD):

"If relaxing the column causes the trim to move, first use main electric trim to remove control column forces, then set stabilizer trim switches to CUTOUT."

"Electric stabilizer trim MUST be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can possibly be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT. However, manual stabilizer trim be not be possible at high speeds."
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 9:06 pm

planecane wrote:
I don't know what document that is an image of but the following is a link to the EAD residing on the FAA website. It does not look the same as what you posted (aside from the fact that you didn't include the actual procedure part of the document anyway). http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf

Yes it don't look the same and this is an another aspect of the problem: there exists multiples version of the procedure.
That said, the FAA's EAD document you linked have the exact same structure: the stab trim neutralization is into the indented paragraph prefixed by "Note:" But to add to the confusion, the so important part is now near the end of the longer note...
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 21, 2019 10:08 pm

PixelFlight wrote:
planecane wrote:
I don't know what document that is an image of but the following is a link to the EAD residing on the FAA website. It does not look the same as what you posted (aside from the fact that you didn't include the actual procedure part of the document anyway). http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf

Yes it don't look the same and this is an another aspect of the problem: there exists multiples version of the procedure.
That said, the FAA's EAD document you linked have the exact same structure: the stab trim neutralization is into the indented paragraph prefixed by "Note:" But to add to the confusion, the so important part is now near the end of the longer note...

Why don't you guys argue around the actual implementation in the ETH FCOM extraction appended to the Preliminary Report. This is what the crew would actually be using.

Ray
 
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7BOEING7
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 12:53 am

XRAYretired wrote:
PixelFlight wrote:
planecane wrote:
I don't know what document that is an image of but the following is a link to the EAD residing on the FAA website. It does not look the same as what you posted (aside from the fact that you didn't include the actual procedure part of the document anyway). http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf

Yes it don't look the same and this is an another aspect of the problem: there exists multiples version of the procedure.
That said, the FAA's EAD document you linked have the exact same structure: the stab trim neutralization is into the indented paragraph prefixed by "Note:" But to add to the confusion, the so important part is now near the end of the longer note...

Why don't you guys argue around the actual implementation in the ETH FCOM extraction appended to the Preliminary Report. This is what the crew would actually be using.

Ray


:checkmark:

What you're arguing over is information that goes in the AFM (Airplane Flight Manual) -- aircrews don't normally deal with the AFM.

What you need to discuss is the Bulletin Boeing would have sent to all operators which goes in the FCOM Vol 2 (Flight Crew Operations Manual) which flight crews do deal with every day, and which would have discussed the issue and provided modified checklist(s) as necessary. The bulletin, the NNC (Non Normal Checklist) for "Runaway Stabilizer"and the "Unreliable Airspeed" NNC (which the ETH crew appeared to not have complied with fully) should be the areas of discussion. I would think every MAx driver would have
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 1:09 am

7BOEING7 wrote:
XRAYretired wrote:
PixelFlight wrote:
Yes it don't look the same and this is an another aspect of the problem: there exists multiples version of the procedure.
That said, the FAA's EAD document you linked have the exact same structure: the stab trim neutralization is into the indented paragraph prefixed by "Note:" But to add to the confusion, the so important part is now near the end of the longer note...

Why don't you guys argue around the actual implementation in the ETH FCOM extraction appended to the Preliminary Report. This is what the crew would actually be using.

Ray


:checkmark:

What you're arguing over is information that goes in the AFM (Airplane Flight Manual) -- aircrews don't normally deal with the AFM.

What you need to discuss is the Bulletin Boeing would have sent to all operators which goes in the FCOM Vol 2 (Flight Crew Operations Manual) which flight crews do deal with every day, and which would have discussed the issue and provided modified checklist(s) as necessary. The bulletin, the NNC (Non Normal Checklist) for "Runaway Stabilizer"and the "Unreliable Airspeed" NNC (which the ETH crew appeared to not have complied with fully) should be the areas of discussion. I would think every MAx driver would have

You make a good point. Have you seen any of those available to look at?
 
speedking
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 1:29 am

According to https://www.satcom.guru/2018/11/stabilizer-trim.html the column cutout switches would disable any electric trim if the column is moved enough to compensate wrong trim. At which column position would this happen? Is it so that during the last 20 seconds of the final dive when the pilots pulled the columns full, the electric trim was disabled?
 
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7BOEING7
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 1:43 am

speedking wrote:
According to https://www.satcom.guru/2018/11/stabilizer-trim.html the column cutout switches would disable any electric trim if the column is moved enough to compensate wrong trim. At which column position would this happen? Is it so that during the last 20 seconds of the final dive when the pilots pulled the columns full, the electric trim was disabled?


My understanding is that doesn’t apply when MCAS is operating but other than that any time the trim is operating and you pull the opposite direction it stops — it doesn’t take much and is part of the preflight checks done by the Boeing flightcrew before the airplane makes its first flight.
 
Some1Somewhere
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 7:08 am

flybucky wrote:
planecane wrote:
It is not a suggestion. It explicitly says to use the main electric trim. I don't know how much more clear it could be.

It may be clear to you and others, but it could definitely could have been written to be more clear. ET302 did use Electric Trim before Stab Trim Cutout. They just didn't use it enough. Here's a breakdown of the first paragraph of the EAD as it applied to ET302:

"Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required."

ET302 did disengage AP. And they did control the pitch attitude with a combination of the control column and main electric trim. They were able to hold the Pitch Attitude between 0 to 5º.

"If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT."

Relaxing the column was causing the trim to move, so they set the Stab Trim to Cutout.

If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually.

From the best we can tell from the FDR and CVR, ET302 did attempt to trim the plane manually with the trim wheel, unsuccessfully.

If the EAD were written this way, it would have been explicitly clear with no room for misinterpretation (my edits in BOLD):

"If relaxing the column causes the trim to move, first use main electric trim to remove control column forces, then set stabilizer trim switches to CUTOUT."

"Electric stabilizer trim MUST be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can possibly be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT. However, manual stabilizer trim be not be possible at high speeds."

The problem with writing it like that is that this is the generic runaway stabiliser checklist, not something specific to MCAS. So in the event of a hardware failure (jammed switch, failed motor controller, blown up motor etc.), effective use of electric trim may be completely impossible.

This is a result of Boeing's decision to treat the end result of MCAS (runaway stabiliser), not somewhere further up the causal chain. That's not necessarily a bad decision (because diagnosing a specific sensor or ADIRU failure in the air isn't easy), but it does mean that the procedure has to be very generic and can't assume that it was MCAS that caused the runaway, because we don't know it's MCAS.

One option would be restore the NG configuration of cutout switches, with one disabling just the FCC (A/P, STS, MCAS) inputs and one disabling the whole system. That way, electric trim is still available in the event of an FCC issue, be it persistent MCAS, an STS failure, or any other issue.

Then your procedure could have an additional step. I wonder why this wasn't written on the NG/previous versions, as they spent the money to have a second switch, but this is roughly what I'd write: (updates in bold)
  1. Control column. . . . . . . . . . . . . . . . . ​ Hold firmly​
  2. Autopilot​ (if engaged)​ .​ . . . . . . . . . . . .Disengage​
    Do not​ re-engage the autopilot.​
    Control airplane pitch attitude manually with ​
    control column and main​ electric trim as​ ​
    needed.​
  3. If the runaway stops​:
    ■​ ■​ ■​ ■​
  4. If the runaway continues:
    STAB TRIM AUTOPILOT CUTOUT ​
    switch ​ . . . . . . . . . . . . . . . . CUTOUT​


    Control airplane pitch attitude manually with ​
    control column and main​ electric trim as​ ​
    needed.​
  5. If the runaway stops:
    ■​ ■​ ■​ ■​
  6. If the runaway continues:
    STAB TRIM MAIN ELECT CUTOUT
    switch . . . . . . . . . . . . . . . . CUTOUT​


    Control airplane pitch attitude manually with ​
    control column and manual trim wheel as​ ​
    needed.​[/b]

    If the runaway stops:
    ■​ ■​ ■​ ■​
  7. If the runaway continues:​
    Stabilizer ​trim wheel...grasp and hold

(original taken from p.143 of a 737NG here, but this is probably outdated. A post here has a different version with references to autothrottle.

This does of course re-raise the question of flying the 737, NG or newer, with no electric trim available at all. Have there been any/many cases of runaway stabiliser or failed electric trim shortly after takeoff?
 
Ertro
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 7:45 am

Some1Somewhere wrote:
One option would be restore the NG configuration of cutout switches, with one disabling just the FCC (A/P, STS, MCAS) inputs and one disabling the whole system. That way, electric trim is still available in the event of an FCC issue, be it persistent MCAS, an STS failure, or any other issue.


This cutout switch situation to me is the most mysterious of all and shows that there still is something really significant that we as a public do not know about this system.

When Boeing desperately wants to shoehorn a plane into grandfathered approval process and to avoid simulator time at all costs and has shown willingness to go to great lengths to hide some changes I am pretty sure they had a rule that absolutely zero additional visible changes gets made for some "feelgood" reason and every little additional change needs a really really bulletproof justification and needs approval of N committees to doublecheck whether the very very good justification really exists.

What could have been the very very good reason why the cutout switches had to be changed from the NG switch configuration to a new one in MAX?
What was so terribly wrong about having NG style cutout switches with a MAX with MCAS that they needed to be changed?

Unless this question gets a good answer there still is something very significant about something related to MCAS that we public still are not told about and because of that stating anything for sure about the fix and regulatory approvals seems futile.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 8:12 am

Ertro wrote:
Some1Somewhere wrote:
One option would be restore the NG configuration of cutout switches, with one disabling just the FCC (A/P, STS, MCAS) inputs and one disabling the whole system. That way, electric trim is still available in the event of an FCC issue, be it persistent MCAS, an STS failure, or any other issue.


This cutout switch situation to me is the most mysterious of all and shows that there still is something really significant that we as a public do not know about this system.

When Boeing desperately wants to shoehorn a plane into grandfathered approval process and to avoid simulator time at all costs and has shown willingness to go to great lengths to hide some changes I am pretty sure they had a rule that absolutely zero additional visible changes gets made for some "feelgood" reason and every little additional change needs a really really bulletproof justification and needs approval of N committees to doublecheck whether the very very good justification really exists.

What could have been the very very good reason why the cutout switches had to be changed from the NG switch configuration to a new one in MAX?
What was so terribly wrong about having NG style cutout switches with a MAX with MCAS that they needed to be changed?


Unless this question gets a good answer there still is something very significant about something related to MCAS that we public still are not told about and because of that stating anything for sure about the fix and regulatory approvals seems futile.


Perhaps there was some concern for the authority they had given MCAS and they did need a means to switch it off with acceptable reliability numbers, a 'new' switch was not acceptable and they needed two switches to make the numbers (i.e. One Cut-Out switch and one 'new' off switch or both Cut-Out switches re-purposed).

Ray
 
Some1Somewhere
Posts: 28
Joined: Thu Jun 25, 2015 2:22 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 8:38 am

XRAYretired wrote:
Ertro wrote:
Some1Somewhere wrote:
One option would be restore the NG configuration of cutout switches, with one disabling just the FCC (A/P, STS, MCAS) inputs and one disabling the whole system. That way, electric trim is still available in the event of an FCC issue, be it persistent MCAS, an STS failure, or any other issue.


This cutout switch situation to me is the most mysterious of all and shows that there still is something really significant that we as a public do not know about this system.

When Boeing desperately wants to shoehorn a plane into grandfathered approval process and to avoid simulator time at all costs and has shown willingness to go to great lengths to hide some changes I am pretty sure they had a rule that absolutely zero additional visible changes gets made for some "feelgood" reason and every little additional change needs a really really bulletproof justification and needs approval of N committees to doublecheck whether the very very good justification really exists.

What could have been the very very good reason why the cutout switches had to be changed from the NG switch configuration to a new one in MAX?
What was so terribly wrong about having NG style cutout switches with a MAX with MCAS that they needed to be changed?


Unless this question gets a good answer there still is something very significant about something related to MCAS that we public still are not told about and because of that stating anything for sure about the fix and regulatory approvals seems futile.


Perhaps there was some concern for the authority they had given MCAS and they did need a means to switch it off with acceptable reliability numbers, a 'new' switch was not acceptable and they needed two switches to make the numbers (i.e. One Cut-Out switch and one 'new' off switch or both Cut-Out switches re-purposed).

Ray


The diagrams and descriptions previously posted imply that either switch in the 737NG config would have disabled MCAS. The A/P switch disconnects the signal outputs from the FCCs from the motor controller. The MAIN ELECT switch disconnects power to the contactor providing the motor controller with power.

In the MAX config, both switches apparently disconnect power to the contactor. Arguably, this is less redundant as e.g. a welded contactor could occur, and the NG config would at least allow you to stop signals getting to the controller.

The chances of a switch failing in that manner though are... pretty slim.
 
planecane
Posts: 1142
Joined: Thu Feb 09, 2017 4:58 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 2:51 pm

Ertro wrote:
Some1Somewhere wrote:
One option would be restore the NG configuration of cutout switches, with one disabling just the FCC (A/P, STS, MCAS) inputs and one disabling the whole system. That way, electric trim is still available in the event of an FCC issue, be it persistent MCAS, an STS failure, or any other issue.


This cutout switch situation to me is the most mysterious of all and shows that there still is something really significant that we as a public do not know about this system.

When Boeing desperately wants to shoehorn a plane into grandfathered approval process and to avoid simulator time at all costs and has shown willingness to go to great lengths to hide some changes I am pretty sure they had a rule that absolutely zero additional visible changes gets made for some "feelgood" reason and every little additional change needs a really really bulletproof justification and needs approval of N committees to doublecheck whether the very very good justification really exists.

What could have been the very very good reason why the cutout switches had to be changed from the NG switch configuration to a new one in MAX?
What was so terribly wrong about having NG style cutout switches with a MAX with MCAS that they needed to be changed?

Unless this question gets a good answer there still is something very significant about something related to MCAS that we public still are not told about and because of that stating anything for sure about the fix and regulatory approvals seems futile.


Based on the block diagram (from memory) the autopilot signal path and the MCAS signal path are the same. The NG cutout switch configuration would turn off MCAS with the autopilot. Given what we know now, that might be a good thing but if MCAS is supposed to operate in manual flight I can see why they changed the switch configuration. They wanted MCAS to be invisible and didn't want it to be disabled when autopilot trim was disabled since the pilots would be hand flying at that point which is what MCAS was designed for.

In hindsight, it makes no sense because you cut it off with autopilot anyway now. I agree that the switches should be reconfigured to be one for all automatic trim and one for manual electric trim.
 
Saintor
Posts: 29
Joined: Wed Mar 13, 2019 10:35 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 4:36 pm

From the best we can tell from the FDR and CVR, ET302 did attempt to trim the plane manually with the trim wheel, unsuccessfully.


... possibly because of overspeed? Were they aware that it couldn't be done at 300-350 knots (without the roller coaster option maybe) is a good question. Is it common knowledge that manual trimming on a 737 can't be realistically done at higher than 250 as some articles reported.
 
fadecfault
Posts: 164
Joined: Mon Nov 05, 2007 8:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 22, 2019 9:08 pm

sgrow787 wrote:
fadecfault wrote:
No the symds are not intergrated with the fccs. No it does not get aoa from the adiru.

This is what happens when you have bad information.


Well what is YOUR source?


Me.
Image
The views and opinions written here are my own and do not reflect those of my employer.
 
9Patch
Posts: 341
Joined: Wed Mar 13, 2019 10:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 2:28 am

Interested wrote:
It's in the news today that 3 agencies, 8 countries plus Europe are together reviewing how the Max 737 was ever certified safe to fly in the first place

Old news to EVERYONE except you, apparently.
 
sgrow787
Posts: 262
Joined: Fri May 16, 2014 8:12 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 4:40 am

fadecfault wrote:
sgrow787 wrote:
fadecfault wrote:
No the symds are not intergrated with the fccs. No it does not get aoa from the adiru.

This is what happens when you have bad information.


Well what is YOUR source?


Me.
Image


Well, (a) it says "System Differences Volume 1", which could mean the circled item is a difference - it's on the NG and not on the Max, and (b) the presence of a separate SMYD doesn't necessarily mean a straight AOA connection. Either way, the aforementioned block diagram shows ADIRU connected to SMYD.

You.
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
XRAYretired
Posts: 626
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 8:24 am

sgrow787 wrote:
fadecfault wrote:
sgrow787 wrote:

Well what is YOUR source?


Me.
Image


Well, (a) it says "System Differences Volume 1", which could mean the circled item is a difference - it's on the NG and not on the Max, and (b) the presence of a separate SMYD doesn't necessarily mean a straight AOA connection. Either way, the aforementioned block diagram shows ADIRU connected to SMYD.

You.


Just to be fair, I'm sure fadecfault applied the circle to the diagram to highlight the SYMDs for us. The MAX block diagram in the Preliminary Report also shows the SYMD as a separte entity to the FCC and connection between AIDRU and SYMD which we know must include Airspeed and Altitude, but not necessarily AOA signal. The AOA or other external signals are not shown on the block diagram.

I would take the view that the arrangement is the same as NG, and so, if the AOA analogue is connected to both the AIDRU and SMYD for NG, there would seem no tangible reason why they would change this for MAX?


Ray
 
User avatar
InsideMan
Posts: 334
Joined: Thu Aug 04, 2011 9:49 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 9:13 am

zeke wrote:

To be clear the original MCAS implementation was not dangerous if the sensors were working, it is only after a AOA failure case, and again after the crew failed to perform mandatory procedure (unreliable airspeed) that this MCAS issue raised its head. MCAS should be as invisible to the crew as a yaw dampener.

To me the engineering fix is easy, what worries me is the human factors issues as to why multiple crews did not perform their required procedures.

To be further clear, MCAS did not operate with flaps down, why didn’t the pilots deal with the stick shaker immediately?


So you were comfortable with a system relying on one sensor input taking trim authority away from you repeatedly all while autopilot is off? I thought that was the whole argument of B pilots vs A pilots that Boeing let's you actually fly the aircraft as is.

If you had been the pilot on the Ethiopian flight, what would you have done differently? As far as I can tell they did follow the procedure....

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