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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 10:30 am

Some1Somewhere wrote:
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 B737 MAX STAB TRIM CUTOUT switches not only cut the 28V STAB TRIM CONTROL signal that energize the R64 STAB TRIM CONT RELAY (providing the 3 phases 115V power to the stab trim motor) but also the other 28V signal that end into the CUTOUT SIGNAL input of the FCC A/B. To be verified but it seem logical that the FCC don't generate stab trim commands if that input is not 28V anymore. In that case the redundancy is that same as on the NG in the event of a welded contacts on R64.
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 10:42 am

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

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...

XRAYretired wrote:
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.

7BOEING7 wrote:
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.

Great points by everyone. I didn't realize there were so many variations of similar documents. No wonder there is so much disagreement.

Here's a list of the variations of the documentation:

1. Nov 6, 2018 TBC-19. This is the FCOM (Flight Crew Operations Manual) bulletin issued by Boeing. This does not explicitly mention using Electric Trim before Stab Trim Cutout, it is only mentioned in an indented Note. FCOM is what flights crews are familiar with on a daily basis.

Image

2. Nov 7, 2018 FAA AD 2018-23-51. This is the FAA Emergency Airworthiness Directive which includes a revision of the AFM (Airplane Flight Manual). This does mention using the Electric Trim to control pitch attitude in the first sentence. Flight crews typically do not deal with the AFM.

Image

3. ET AFM (Prelim Report Appendix 2). This matches the EAD (which includes the revision to the AFM).

Image

4. ET FCOM (Prelim Report Appendix 4). This matches the Boeing FCOM bulletin.

Image

Conclusion: ET's AFM and FCOM were updated properly. Flight crews typically deal with FCOM, not AFM. The FCOM Operating Instructions' first sentence does not mention using Electric Trim before Stab Trim Cutout. It is only optionally suggested in a Note.
 
sgrow787
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 1:28 pm

XRAYretired wrote:
Just to be fair, I'm sure fadecfault applied the circle to the diagram to highlight the SYMDs for us.


We should let him make that statement, assuming he's willing to speak in more than a few words at a time.

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.


AOA would be passed on along with computed air data to the FCC (and, from the block diagram, to the SMYD).

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?


Although it's possible a faulty/intermittent AOA in and of itself could cause the good-value blips in the air data at 05:43:27 and 05:43:37 for the ET302 crash, the fact that the airspeed on the affected side is lower than the non-affected side tells us the ADIRU is faulty.

As for whether they maintained the external AOA connection to the SMYD, I suppose that's a reasonable consideration, and it seems to be supported by what was seen in the JT610 crash... the stick shaker stopped when air speed peaked at 23:22:43, while AOA was still showing 20 deg offset. Ie, if the AOA sensor was faulty (and not the ADIRU) then wouldn't the stick shaker (which is from the SMYD) have continued to shake on the JT610 flight due to the AOA value it was receiving?

So no, I'm sticking with my theory that it's the ADIRU on both flights, and I'm betting both aircraft were produced from the North Charleston plant.
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
mzlin
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 2:41 pm

sgrow787 wrote:
XRAYretired wrote:
Just to be fair, I'm sure fadecfault applied the circle to the diagram to highlight the SYMDs for us.


We should let him make that statement, assuming he's willing to speak in more than a few words at a time.

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.


AOA would be passed on along with computed air data to the FCC (and, from the block diagram, to the SMYD).

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?


Although it's possible a faulty/intermittent AOA in and of itself could cause the good-value blips in the air data at 05:43:27 and 05:43:37 for the ET302 crash, the fact that the airspeed on the affected side is lower than the non-affected side tells us the ADIRU is faulty.

As for whether they maintained the external AOA connection to the SMYD, I suppose that's a reasonable consideration, and it seems to be supported by what was seen in the JT610 crash... the stick shaker stopped when air speed peaked at 23:22:43, while AOA was still showing 20 deg offset. Ie, if the AOA sensor was faulty (and not the ADIRU) then wouldn't the stick shaker (which is from the SMYD) have continued to shake on the JT610 flight due to the AOA value it was receiving?

So no, I'm sticking with my theory that it's the ADIRU on both flights, and I'm betting both aircraft were produced from the North Charleston plant.


Well your theory is clearly wrong as all 737s are produced in Renton.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 2:50 pm

sgrow787 wrote:
XRAYretired wrote:
Just to be fair, I'm sure fadecfault applied the circle to the diagram to highlight the SYMDs for us.


We should let him make that statement, assuming he's willing to speak in more than a few words at a time.

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.


AOA would be passed on along with computed air data to the FCC (and, from the block diagram, to the SMYD).

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?


Although it's possible a faulty/intermittent AOA in and of itself could cause the good-value blips in the air data at 05:43:27 and 05:43:37 for the ET302 crash, the fact that the airspeed on the affected side is lower than the non-affected side tells us the ADIRU is faulty.

As for whether they maintained the external AOA connection to the SMYD, I suppose that's a reasonable consideration, and it seems to be supported by what was seen in the JT610 crash... the stick shaker stopped when air speed peaked at 23:22:43, while AOA was still showing 20 deg offset. Ie, if the AOA sensor was faulty (and not the ADIRU) then wouldn't the stick shaker (which is from the SMYD) have continued to shake on the JT610 flight due to the AOA value it was receiving?

So no, I'm sticking with my theory that it's the ADIRU on both flights, and I'm betting both aircraft were produced from the North Charleston plant.


OK. I keep getting stuck on the fence depending who's post I last read.

So, if its ADIRU in one or both cases, it still leaves us with what common factor causes it to calculate AOA high, IAS low and Altitude low. Any speculation?

Also would you like to speculate on what might have caused Stick Shaker to drop out on JT610. Was it Airspeed peak do you think?

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

Tue Apr 23, 2019 3:09 pm

flybucky wrote:
Conclusion: ET's AFM and FCOM were updated properly. Flight crews typically deal with FCOM, not AFM. The FCOM Operating Instructions' first sentence does not mention using Electric Trim before Stab Trim Cutout. It is only optionally suggested in a Note.


Again, the note is not suggesting anything. It is describing what trim is available depending on the position of the cutout switches. The ET FCOM that you posted says to "do the Runaway Stabilizer NNC."

Unless it is different that the one I found posted online for the NG, the Runaway Stabilizer NNC is:

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 CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer
trim wheel . . . . . . . . . . Grasp and hold


So, to come full circle on this endless argument, the FCOM says that if there is uncommanded nose down stabilizer trim in the 737-8/-9 to do the Runaway Stabilzer NNC. The third step in the NNC after holding the control column firmly and disengaging the AP is "Control airplane pitch attitude manually with control column and main electric trim as needed."

Step 4 is to move the STAB TRIM CUTOUT switches (both) to CUTOUT. Step 4 is to be performed if the runaway continues. The ET crew moved the switches while they were manually trimming nose up. The uncommanded nose down was not continuing at that point in time.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 3:49 pm

About the procedure document:
"planecane" :checkmark:
"XRAYretired" :checkmark:
"7BOEING7" :checkmark:
"flybucky" :checkmark:
Thank you so much for that fantastic synergy! :thumbsup:
This is really how this forum should be. :)
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 4:05 pm

planecane wrote:
So, to come full circle on this endless argument, the FCOM says that if there is uncommanded nose down stabilizer trim in the 737-8/-9 to do the Runaway Stabilzer NNC. The third step in the NNC after holding the control column firmly and disengaging the AP is "Control airplane pitch attitude manually with control column and main electric trim as needed."

Step 4 is to move the STAB TRIM CUTOUT switches (both) to CUTOUT. Step 4 is to be performed if the runaway continues. The ET crew moved the switches while they were manually trimming nose up. The uncommanded nose down was not continuing at that point in time.

I highly doubt that the 737 MAX Runaway Stabilzer NNC contain instruction to move the STAB TRIM CUTOUT switches (both) to CUTOUT within 5 seconds after the last main electric trim as needed.
After that 5 seconds delay the MCAS will trim again in case of a AoA erratic high value.
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 4:15 pm

PixelFlight wrote:
planecane wrote:
So, to come full circle on this endless argument, the FCOM says that if there is uncommanded nose down stabilizer trim in the 737-8/-9 to do the Runaway Stabilzer NNC. The third step in the NNC after holding the control column firmly and disengaging the AP is "Control airplane pitch attitude manually with control column and main electric trim as needed."

Step 4 is to move the STAB TRIM CUTOUT switches (both) to CUTOUT. Step 4 is to be performed if the runaway continues. The ET crew moved the switches while they were manually trimming nose up. The uncommanded nose down was not continuing at that point in time.

I highly doubt that the 737 MAX Runaway Stabilzer NNC contain instruction to move the STAB TRIM CUTOUT switches (both) to CUTOUT within 5 seconds after the last main electric trim as needed.
After that 5 seconds delay the MCAS will trim again in case of a AoA erratic high value.


It does not say that. It says if the runaway continues to do it. Upon getting the aircraft back into trim they would stop trimming manually (electric). Then, 5 seconds later the trim will start to move nose down again. When it starts moving uncommanded, that is when, based on the NNC, they should move the switches to cutout. Only being slightly out of trim at that point, the manual wheel should be viable to maintain trim until they can land.

I agree that to be completely clear to the pilots and leave no room for misunderstanding, the NNC on the MAX should have been updated to say to do that. Or better yet say to use the main electric trim again and move the switches as soon as the aircraft is back in trim.

Regardless, the ET crew did not follow the NNC properly because they moved the switches before reaching that step in the process. I do not disagree that the situation arose due to a design so poorly thought out that it is beyond comprehension as an engineer. Knowing everything I know, if I was on a jury, I would assign a large liability to Boeing for the loss of the victims. However, had the crew performed the NNC properly and done the other NNCs that were necessary, the plane would likely have been saved.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 6:02 pm

planecane wrote:
The third step in the NNC after holding the control column firmly and disengaging the AP is "Control airplane pitch attitude manually with control column and main electric trim as needed."
[...]
Regardless, the ET crew did not follow the NNC properly because they moved the switches before reaching that step in the process.

ET302 pilots did use the main electric trim just before there cutoff the stab trim, but not longer enough. This narrow down there error the the words "as needed". I don't know if we will know someday why there stop the trim at 2,3 units instead of about 5 units, but we have to accept the fact that something lead to that fatal decision. What information the pilots have to evaluate the "as needed" stab trim ?
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 6:23 pm

PixelFlight wrote:
planecane wrote:
The third step in the NNC after holding the control column firmly and disengaging the AP is "Control airplane pitch attitude manually with control column and main electric trim as needed."
[...]
Regardless, the ET crew did not follow the NNC properly because they moved the switches before reaching that step in the process.

ET302 pilots did use the main electric trim just before there cutoff the stab trim, but not longer enough. This narrow down there error the the words "as needed". I don't know if we will know someday why there stop the trim at 2,3 units instead of about 5 units, but we have to accept the fact that something lead to that fatal decision. What information the pilots have to evaluate the "as needed" stab trim ?


Without the complete CVR transcript, it is difficult to say what led to the decision. My suspician is that the FO remembered the emphasis on making sure to move the switches to cutout and when he asked the captain, the captain was distracted by all of the warnings, stick shaker and other instrument errors and also remembered the emphasis on the cutout and answered in the affirmative.

The fact that the captain was holding the column with a lot of back pressure indicates that the main electric trim was definitely still needed.
 
fadecfault
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 7:30 pm

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.


Obviously you don't have any sort of aircraft experience let alone 737 experience. I have nearly 20 years working on the 737 and I have worked the max. The notion they would show a NG diagram in a MAX training manual is ridiculous. It's blatantly clear to me the picture I posted is of a MAX because 1) The Symd locations have moved. 2) A SEU is in the place of where the symds would normally be. But then again I have the experience to know this.
So you can continue to listen to the talking heads on youtube who have little to no technical data or you can trust what I am saying because I have access to actual data.
The symd functionality has not changed from NG to MAX and is not even mentioned in the differences manual but you want claim otherwise with no actual information to back it up. No your diagram does not show the stick shaker system, No I can not and will not post the boeing SSM because it's propriety information.
The views and opinions written here are my own and do not reflect those of my employer.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Tue Apr 23, 2019 8:13 pm

fadecfault wrote:
I have nearly 20 years working on the 737 and I have worked the max. [...] I have access to actual data.
No I can not and will not post the boeing SSM because it's propriety information.

Did you have the opportunity to describes how the FCC's MCAS commands are physically send to the stab trim motor ? From the published 737 MAX schematic the MCAs commands are not send on the discrete electric stab trim signals connected to the thumb switches and are not send either on the discrete electric stab trim signals from the FCC (autopilot ?) that pass through the column switches cutoff. Could be a digital link ?
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 8:08 am

fadecfault wrote:
sgrow787 wrote:
fadecfault wrote:

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.


Obviously you don't have any sort of aircraft experience let alone 737 experience. I have nearly 20 years working on the 737 and I have worked the max. The notion they would show a NG diagram in a MAX training manual is ridiculous. It's blatantly clear to me the picture I posted is of a MAX because 1) The Symd locations have moved. 2) A SEU is in the place of where the symds would normally be. But then again I have the experience to know this.
So you can continue to listen to the talking heads on youtube who have little to no technical data or you can trust what I am saying because I have access to actual data.
The symd functionality has not changed from NG to MAX and is not even mentioned in the differences manual but you want claim otherwise with no actual information to back it up. No your diagram does not show the stick shaker system, No I can not and will not post the boeing SSM because it's propriety information.

Can you speculate (give away any secrets) as to why the IAS is low on the affected side with high AOA?

Ta.

Ray
Last edited by XRAYretired on Wed Apr 24, 2019 8:33 am, edited 1 time in total.
 
Waterbomber2
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 8:21 am

It's amazing that the discussion is carrying on 40 days after the crash.
This must be the mother of all threads.
 
sgrow787
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 8:34 am

fadecfault wrote:
Obviously you don't have any sort of aircraft experience let alone 737 experience. I have nearly 20 years working on the 737 and I have worked the max.


I've stated my 15 yrs experience is in commercial aerospace software design. In what capacity is your nearly 20 years experience in? Judging by the defensive posture I'm guessing maintenance, which means you understand what LRUs exist on a particular aircraft, and how they are connected. You may even know how to run tests on different LRUs to determine if they're bad. But maybe you don't understand what makes some of these LRUs work.

fadecfault wrote:
The notion they would show a NG diagram in a MAX training manual is ridiculous. It's blatantly clear to me the picture I posted is of a MAX because 1) The Symd locations have moved. 2) A SEU is in the place of where the symds would normally be. But then again I have the experience to know this.


I have no idea about the diagram you posted because you didn't include your interpretation of it, or even the context.

fadecfault wrote:
So you can continue to listen to the talking heads on youtube who have little to no technical data or you can trust what I am saying because I have access to actual data.


You have access to actual data but you can't share because it's proprietary, even though you're posting under an anonymous id. I feel sorry for you but unless you can present a reference that I can look at, your experience don't mean squat to me. On the contrary, since your experience is Boeing specific, I'm inclined to consider what you have to say with a grain of salt. And if the discussions on a.net are getting to you, perhaps you should move on to something else.

fadecfault wrote:
The symd functionality has not changed from NG to MAX and is not even mentioned in the differences manual but you want claim otherwise with no actual information to back it up. No your diagram does not show the stick shaker system, No I can not and will not post the boeing SSM because it's propriety information.


I've already conceded the SMYD could be a separate LRU, since (a) it's depicted as such in the system diagram with a connection to the ADIRU, and (b) it doesn't really have any relevance to my theory on the ADIRU.

You seem to be stuck on the SMYD. Yet you haven't acknowledged yet what I have to say on the other things.
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
sgrow787
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 8:47 am

mzlin wrote:
Well your theory is clearly wrong as all 737s are produced in Renton.


I must have stayed up too late last night. Got things confused with the engine nacelles story that I read. Thanks for pointing it out. Let me change my bet to both planes suffering from poor ADIRU installation processes.

Edit: With 52 Max planes being produced per month out of the Renton, would it be fair to say they could be experiencing the same or similar quality issues as seen at the North Charleston location?
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
xmp125a
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 8:55 am

Waterbomber2 wrote:
It's amazing that the discussion is carrying on 40 days after the crash.
This must be the mother of all threads.


MentourPilot (re?) posted the previously deleted video on how difficult is to manually trim the 737NG. https://www.youtube.com/watch?v=aoNOVlxJmow

I don't know if it is a deleted video, it seems that this is the same sim session, but he added the new introduction. It would imply that ET faced almost impossible job retrimming the plane if they relied on manual trim. So once airspeed increased they were in hopeless situation. I would understand why they reenabled electrical trim, they knew they will gonna crash anyway with no vertical control of the plane.
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 9:58 am

PixelFlight wrote:
About the procedure document:
"planecane" :checkmark:
"XRAYretired" :checkmark:
"7BOEING7" :checkmark:
"flybucky" :checkmark:
Thank you so much for that fantastic synergy! :thumbsup: This is really how this forum should be. :)

I concur. Sometimes the discussion can get derailed, but overall the synergy definitely allows us to learn more together than alone!
 
flybucky
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 10:09 am

planecane wrote:
Unless it is different that the one I found posted online for the NG, the Runaway Stabilizer NNC is

I see your point. Just for reference, here is the Runaway Stabilizer checklist for 737 MAX, from the ET302 Prelim Report Appendix 3. There are some differences from NG, but nothing major. (Here is also a link to the original post with the other docs like FCOM and EAD.)

Image
 
OldAeroGuy
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 12:27 pm

xmp125a wrote:
So once airspeed increased they were in hopeless situation. I would understand why they reenabled electrical trim, they knew they will gonna crash anyway with no vertical control of the plane.


Reducing thrust was another option. Thrust has a powerful effect on vertical performance.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
xmp125a
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 1:24 pm

OldAeroGuy wrote:
xmp125a wrote:
So once airspeed increased they were in hopeless situation. I would understand why they reenabled electrical trim, they knew they will gonna crash anyway with no vertical control of the plane.


Reducing thrust was another option. Thrust has a powerful effect on vertical performance.


It does. But it points you downwards :) I think their fate was sealed after speed increased to the point where manual trim was unusable.
 
aljrooney
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 3:44 pm

I did a quick search....Anyone seen this?
http://www.youtube.com/watch?v=HWZhbsGHBss
FAA grounded Cirrus Vision Jets
Some similarities and issue with AOA installation?

Edit for spelling mistakes DOH
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 7:05 pm

xmp125a wrote:
OldAeroGuy wrote:
xmp125a wrote:
So once airspeed increased they were in hopeless situation. I would understand why they reenabled electrical trim, they knew they will gonna crash anyway with no vertical control of the plane.


Reducing thrust was another option. Thrust has a powerful effect on vertical performance.


It does. But it points you downwards :) I think their fate was sealed after speed increased to the point where manual trim was unusable.



There are pilot reports that that is not necessarily so at least with small thrust changes in a climb. I'm sure if you chopped Thrust to 50% it would pitch down after a few seconds - but if you were to gradually bring it down while still climbing it should have required less up elevator pressure to counteract the Horizontal Stabilizer down as airspeed over the tail decreased - possibly allowing you to use manual wheel trim at the point where you were back in the normal airspeed climb range (240ish knots).

In any case the MAX should be less susceptible to changes in Thrust than the NG as one of the Benefits of moving the Engines Higher is the Thrust line moves higher as well and is closer to the center of Gravity. The lift of the Bigger Nacelle should help as well to keep the nose high when you reduce thrust.
 
OldAeroGuy
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 7:46 pm

morrisond wrote:
xmp125a wrote:
OldAeroGuy wrote:

Reducing thrust was another option. Thrust has a powerful effect on vertical performance.


It does. But it points you downwards :) I think their fate was sealed after speed increased to the point where manual trim was unusable.



There are pilot reports that that is not necessarily so at least with small thrust changes in a climb. I'm sure if you chopped Thrust to 50% it would pitch down after a few seconds - but if you were to gradually bring it down while still climbing it should have required less up elevator pressure to counteract the Horizontal Stabilizer down as airspeed over the tail decreased - possibly allowing you to use manual wheel trim at the point where you were back in the normal airspeed climb range (240ish knots).

In any case the MAX should be less susceptible to changes in Thrust than the NG as one of the Benefits of moving the Engines Higher is the Thrust line moves higher as well and is closer to the center of Gravity. The lift of the Bigger Nacelle should help as well to keep the nose high when you reduce thrust.

:checkmark:
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
mzlin
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 24, 2019 9:58 pm

sgrow787 wrote:
mzlin wrote:
Well your theory is clearly wrong as all 737s are produced in Renton.


I must have stayed up too late last night. Got things confused with the engine nacelles story that I read. Thanks for pointing it out. Let me change my bet to both planes suffering from poor ADIRU installation processes.

Edit: With 52 Max planes being produced per month out of the Renton, would it be fair to say they could be experiencing the same or similar quality issues as seen at the North Charleston location?


You're welcome. I should not have been so curt about it.

I think the timing of the AOA fault in ET302 is more indicative of a bird strike whereas the LT flight had ongoing issues that were not corrected by AOA indicator replacement and could fit with a ADIRU problem or a problem with wiring from gauge to ADIRU.

I think if Renton workers felt pressured to cut corners during assembly, that story would have come out by now. Of course, it still could. If the AOA indicator and its wiring are unchanged from NG, and NG has never had a problem in ADIRU or its inputs from the AOA indicator, then it would be exceedingly unlikely to be the issue. But there's a first time for everything.
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 25, 2019 12:31 am

flybucky wrote:
planecane wrote:
Unless it is different that the one I found posted online for the NG, the Runaway Stabilizer NNC is

I see your point. Just for reference, here is the Runaway Stabilizer checklist for 737 MAX, from the ET302 Prelim Report Appendix 3. There are some differences from NG, but nothing major. (Here is also a link to the original post with the other docs like FCOM and EAD.)

Image


It bothers me that the NNC is slightly different for the MAX. If the only training is a short differences training, I would think memory items like the runaway stabilizer NNC should be the exact same between NG and MAX.

I think this MAX version you posted is less clear that the cutout switches should only be moved after balancing control forces. Having never been trained on a 737 (except for a 2 hour simulator session as a brithday present) or any aircraft, I don't know how the NNC is actually trained. Can any NG pilot answer if the training on runaway stabilizer is to get the aircraft in trim before moving to the next step?
 
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7BOEING7
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 25, 2019 2:07 am

planecane wrote:
flybucky wrote:
planecane wrote:
Unless it is different that the one I found posted online for the NG, the Runaway Stabilizer NNC is

I see your point. Just for reference, here is the Runaway Stabilizer checklist for 737 MAX, from the ET302 Prelim Report Appendix 3. There are some differences from NG, but nothing major. (Here is also a link to the original post with the other docs like FCOM and EAD.)

Image


It bothers me that the NNC is slightly different for the MAX. If the only training is a short differences training, I would think memory items like the runaway stabilizer NNC should be the exact same between NG and MAX.

I think this MAX version you posted is less clear that the cutout switches should only be moved after balancing control forces. Having never been trained on a 737 (except for a 2 hour simulator session as a brithday present) or any aircraft, I don't know how the NNC is actually trained. Can any NG pilot answer if the training on runaway stabilizer is to get the aircraft in trim before moving to the next step?


They are the same for all intents and purposes.

As of at least 2008 for the -200 and on the NNC for Runaway Stabilizer is almost exactly the same as the MAX NNC, only differences is the Autothrottle step and the verbiage "after the autopilot is disengaged" in Step 5, which I'm guessing in all models was added more recently than 10 years ago.

"Control airplane pitch attitude manually...." is basically telling the pilot to fly the airplane which would indicate having it in trim. If the runaway continues the flight crew will have the STAB TRIM CUTOUT switches to CUTOUT almost immediately so the airplane will still be relatively "in trim".
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 25, 2019 12:37 pm

mzlin wrote:
sgrow787 wrote:
mzlin wrote:
Well your theory is clearly wrong as all 737s are produced in Renton.


I must have stayed up too late last night. Got things confused with the engine nacelles story that I read. Thanks for pointing it out. Let me change my bet to both planes suffering from poor ADIRU installation processes.

Edit: With 52 Max planes being produced per month out of the Renton, would it be fair to say they could be experiencing the same or similar quality issues as seen at the North Charleston location?


You're welcome. I should not have been so curt about it.

I think the timing of the AOA fault in ET302 is more indicative of a bird strike whereas the LT flight had ongoing issues that were not corrected by AOA indicator replacement and could fit with a ADIRU problem or a problem with wiring from gauge to ADIRU.

I think if Renton workers felt pressured to cut corners during assembly, that story would have come out by now. Of course, it still could. If the AOA indicator and its wiring are unchanged from NG, and NG has never had a problem in ADIRU or its inputs from the AOA indicator, then it would be exceedingly unlikely to be the issue. But there's a first time for everything.



Just to add to your possibilities, the pre-JT043 sensor may well have been faulty (reported so by Indonesian investigators after visit to Rosemount) and the Maintenence read-out pre-JT043 looks significantly different to what you might expect for AOA stuck 20deg high. Also, credible posts early in the Lion AIr thread demonstarted how an AOA installation error could result in a ~20deg offset.

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

Thu Apr 25, 2019 3:45 pm

https://www.newsy.com/stories/american- ... headlines/


At an April 12 meeting about the 737 MAX, Tajer says the FAA raised eyebrows: telling pilots and airlines the agency didn't test a failure of the 737 MAX's MCAS feature.

"The FAA disclosed to us that the reason it wasn't tested was that Boeing had told them that it was a part of a speed trim system which was so transparent to the pilot that there was no need to test a failure of the MCAS. And they accepted that and therefore they did not test it," Tajer said.

[...]

Tajer says the FAA told pilots they haven't reviewed that recovery checklist since Boeing's very first line of 737's took flight.

"They used the term, 'It's possible that checklist has not been validated and reviewed since 1967,'" he said.

The 737 has seen significant physical changes since then, and Tajer says it's time to revise the checklist.

 
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SomebodyInTLS
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 25, 2019 4:04 pm

RedBob wrote:
https://www.newsy.com/stories/american-airlines-pilots-eye-boeing-faa-amid-bad-headlines/


At an April 12 meeting about the 737 MAX, Tajer says the FAA raised eyebrows: telling pilots and airlines the agency didn't test a failure of the 737 MAX's MCAS feature.

"The FAA disclosed to us that the reason it wasn't tested was that Boeing had told them that it was a part of a speed trim system which was so transparent to the pilot that there was no need to test a failure of the MCAS. And they accepted that and therefore they did not test it," Tajer said.

[...]

Tajer says the FAA told pilots they haven't reviewed that recovery checklist since Boeing's very first line of 737's took flight.

"They used the term, 'It's possible that checklist has not been validated and reviewed since 1967,'" he said.

The 737 has seen significant physical changes since then, and Tajer says it's time to revise the checklist.



Well that just strengthens my existing opinion that MCAS was deliberately executed as "a patch of STS" purely for paperwork and training avoidance reasons (a kind of certification-by-stealth). A more correct implementation would have been through modification of stick force (addressing the stick-lightening issue approaching stall) and presumably some additional system affecting control surfaces (inlcuding additional alerts etc.) to address whatever made them change the MCAS parameters during flight test. Of course, those changes would have entailed additional certification work and changes to training etc.
"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."
 
sgrow787
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Apr 26, 2019 11:42 am

XRAYretired wrote:
Just to add to your possibilities, the pre-JT043 sensor may well have been faulty (reported so by Indonesian investigators after visit to Rosemount) and the Maintenence read-out pre-JT043 looks significantly different to what you might expect for AOA stuck 20deg high. Also, credible posts early in the Lion AIr thread demonstarted how an AOA installation error could result in a ~20deg offset.


I don't believe there has been confirmation yet that the left AOA sensor from the JT610 crash was failed. And to my knowledge, they haven't yet found the left AOA sensor from the ET302 crash.

The Truth: "Erroneous left-side AOA data caused MCAS to push the nose down." Whether that erroneous data was due to a faulty ADIRU, bad wiring connection, or a bad sensor itself, remains to be determined.
Reworded: "Faulty left-side AOA sensor data caused..."
Reworded: "A faulty AOA sensor on the left side caused..."
The twist: "Faulty AOA sensor in Lion Air crash linked to repair shop in Florida."

So you can see how information can get twisted to infer something that has not been proven or substantiated.

Unless someone can show a news article to me that says they sent the sensor off to get tested and it came back faulty, then it's still a possible ADIRU problem.
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Apr 26, 2019 12:00 pm

sgrow787 wrote:
XRAYretired wrote:
Just to add to your possibilities, the pre-JT043 sensor may well have been faulty (reported so by Indonesian investigators after visit to Rosemount) and the Maintenence read-out pre-JT043 looks significantly different to what you might expect for AOA stuck 20deg high. Also, credible posts early in the Lion AIr thread demonstarted how an AOA installation error could result in a ~20deg offset.


I don't believe there has been confirmation yet that the left AOA sensor from the JT610 crash was failed. And to my knowledge, they haven't yet found the left AOA sensor from the ET302 crash.

The Truth: "Erroneous left-side AOA data caused MCAS to push the nose down." Whether that erroneous data was due to a faulty ADIRU, bad wiring connection, or a bad sensor itself, remains to be determined.
Reworded: "Faulty left-side AOA sensor data caused..."
Reworded: "A faulty AOA sensor on the left side caused..."
The twist: "Faulty AOA sensor in Lion Air crash linked to repair shop in Florida."

So you can see how information can get twisted to infer something that has not been proven or substantiated.

Unless someone can show a news article to me that says they sent the sensor off to get tested and it came back faulty, then it's still a possible ADIRU problem.

No dispute here?

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

Fri Apr 26, 2019 10:06 pm

aljrooney wrote:
I did a quick search....Anyone seen this?
http://www.youtube.com/watch?v=HWZhbsGHBss
FAA grounded Cirrus Vision Jets
Some similarities and issue with AOA installation?

These are not the same AOA sensors, but it does sound like an analogous situation.

An AOA failure resulted in erroneous AOA data, which triggered an automatic nose down by the computer system (stall warning and protection system (SWPS) or electronic stability and protection system (ESP)). The root cause was "two set screws that secure the potentiometer shaft to the AOA vane shaft can feature “improper torqueing and no application of thread locker [loctite] to secure the two set screws.”"

https://www.aviationtoday.com/2019/04/1 ... incidents/
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 10:23 am

flybucky wrote:
aljrooney wrote:
I did a quick search....Anyone seen this?
http://www.youtube.com/watch?v=HWZhbsGHBss
FAA grounded Cirrus Vision Jets
Some similarities and issue with AOA installation?

These are not the same AOA sensors, but it does sound like an analogous situation.

An AOA failure resulted in erroneous AOA data, which triggered an automatic nose down by the computer system (stall warning and protection system (SWPS) or electronic stability and protection system (ESP)). The root cause was "two set screws that secure the potentiometer shaft to the AOA vane shaft can feature “improper torqueing and no application of thread locker [loctite] to secure the two set screws.”"

https://www.aviationtoday.com/2019/04/1 ... incidents/


Grounded? What? no crashes, pilots able to control in fault condition. Is this a departure from protocols adopted for MAX? (sarcasm and irony intended).

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

Sat Apr 27, 2019 10:45 am

XRAYretired wrote:
flybucky wrote:
aljrooney wrote:
I did a quick search....Anyone seen this?
http://www.youtube.com/watch?v=HWZhbsGHBss
FAA grounded Cirrus Vision Jets
Some similarities and issue with AOA installation?

These are not the same AOA sensors, but it does sound like an analogous situation.

An AOA failure resulted in erroneous AOA data, which triggered an automatic nose down by the computer system (stall warning and protection system (SWPS) or electronic stability and protection system (ESP)). The root cause was "two set screws that secure the potentiometer shaft to the AOA vane shaft can feature “improper torqueing and no application of thread locker [loctite] to secure the two set screws.”"

https://www.aviationtoday.com/2019/04/1 ... incidents/


Grounded? What? no crashes, pilots able to control in fault condition. Is this a departure from protocols adopted for MAX? (sarcasm and irony intended).

Ray

My understanding of "two set screws that secure the potentiometer shaft to the AOA vane shaft" is that the fault is internal of the AoA sensor, and not an AoA installation issue on the aircraft.
 
Some1Somewhere
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 11:41 am

That one appears to be a manufacturing defect, but it's not hard to imagine an AOA vane where the vane assembly is separate/separable from the electronic pickup, and they can be replaced separately.

I don't know whether the 737's ones are like this or are a single unit. Or someone may have 'serviced' one, with or without proper instructions.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 12:11 pm

XRAYretired wrote:
I don't believe there has been confirmation yet that the left AOA sensor from the JT610 crash was failed. And to my knowledge, they haven't yet found the left AOA sensor from the ET302 crash.

The Truth: "Erroneous left-side AOA data caused MCAS to push the nose down." Whether that erroneous data was due to a faulty ADIRU, bad wiring connection, or a bad sensor itself, remains to be determined.

My understanding of the various information found online is that the ADIRU fault scenario can be ruled out, as the second AoA link connected to the SMYD also produced FDR traces that fully fit the AoA erratic value scenario. The AoA value recorded by the FDR is from the AoA link to the SMYD itself. Various sources go in that direction:
https://www.pprune.org/10435549-post2885.html
https://www.pprune.org/10422910-post258.html
http://bit-player.org/2019/737-the-max-mess
Also for JT610 and ET302. the ADIRU is never suspected in any published documents or declaration from investigators, manufacturer, regulator, or company. All have talked about the AoA sensor.
AoA
| |            /---------------------------------------------------------\
| \---> ADIRU --> FCC --> MCAS ---> STAB TRIM MOTOR --> STAB POSITION ---\|
|                                \---------------------------------------\|
\------> SMYD -----------------------------------------------------------\|
            \-----> STICK SHAKER ----------------------------------------\|
                                                                           \--> FADU --> FDR
 
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zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 12:17 pm

But you have no real idea as none of what you write is your own knowledge. You just present other people’s work as your own.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 12:48 pm

zeke wrote:
But you have no real idea as none of what you write is your own knowledge. You just present other people’s work as your own.

Happy waiting for more information to analyze from peoples out there that feel to know so more than me. :wave:
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 1:13 pm

PixelFlight wrote:
XRAYretired wrote:
I don't believe there has been confirmation yet that the left AOA sensor from the JT610 crash was failed. And to my knowledge, they haven't yet found the left AOA sensor from the ET302 crash.

The Truth: "Erroneous left-side AOA data caused MCAS to push the nose down." Whether that erroneous data was due to a faulty ADIRU, bad wiring connection, or a bad sensor itself, remains to be determined.

My understanding of the various information found online is that the ADIRU fault scenario can be ruled out, as the second AoA link connected to the SMYD also produced FDR traces that fully fit the AoA erratic value scenario. The AoA value recorded by the FDR is from the AoA link to the SMYD itself. Various sources go in that direction:
https://www.pprune.org/10435549-post2885.html
https://www.pprune.org/10422910-post258.html
http://bit-player.org/2019/737-the-max-mess
Also for JT610 and ET302. the ADIRU is never suspected in any published documents or declaration from investigators, manufacturer, regulator, or company. All have talked about the AoA sensor.
AoA
| |            /---------------------------------------------------------\
| \---> ADIRU --> FCC --> MCAS ---> STAB TRIM MOTOR --> STAB POSITION ---\|
|                                \---------------------------------------\|
\------> SMYD -----------------------------------------------------------\|
            \-----> STICK SHAKER ----------------------------------------\|
                                                                           \--> FADU --> FDR

The writings you have attributed to me above are not mine, although I do not necessarily disagree with them.

I recognise the statements regarding AOA analogue being separately routed to ADIRU and SYMD and it is likely that SYMD initiates the Stick Shaker.

The problem I still have in accepting 'not ADIRU' position is why is the affected side IAS is low, when I am being told that AOA high should result in AIS high as well?

Conversely, I have a problem accepting the 'it is AIDRU' position whist I do not have any information identifying what ADIRU problem or other source data used by ADIRU would result in AIS low, Altitude low and AOA high? I am conscious that all three begin at the same time stamp (but could just be related to WOW FALSE).

Ray.
 
sgrow787
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 2:58 pm

PixelFlight wrote:
XRAYretired wrote:
I don't believe there has been confirmation yet that the left AOA sensor from the JT610 crash was failed. And to my knowledge, they haven't yet found the left AOA sensor from the ET302 crash.

The Truth: "Erroneous left-side AOA data caused MCAS to push the nose down." Whether that erroneous data was due to a faulty ADIRU, bad wiring connection, or a bad sensor itself, remains to be determined.

My understanding of the various information found online is that the ADIRU fault scenario can be ruled out, as the second AoA link connected to the SMYD also produced FDR traces that fully fit the AoA erratic value scenario. The AoA value recorded by the FDR is from the AoA link to the SMYD itself. Various sources go in that direction:
https://www.pprune.org/10435549-post2885.html
https://www.pprune.org/10422910-post258.html
http://bit-player.org/2019/737-the-max-mess
Also for JT610 and ET302. the ADIRU is never suspected in any published documents or declaration from investigators, manufacturer, regulator, or company. All have talked about the AoA sensor.
AoA
| |            /---------------------------------------------------------\
| \---> ADIRU --> FCC --> MCAS ---> STAB TRIM MOTOR --> STAB POSITION ---\|
|                                \---------------------------------------\|
\------> SMYD -----------------------------------------------------------\|
            \-----> STICK SHAKER ----------------------------------------\|
                                                                           \--> FADU --> FDR


Looks like you edited the nested quote block improperly, since the quote is from me and not XRay (who sees through everything??).

I've got to go in to work today, so I'll get back to you. I get to review a HUD AOA Staple design for a 757 project today.

(I would have added the link from ADIRU to SMYD, since the system block diagram shows that connection, and because the SMYD needs airspeed to make it's decision on stick shaker.)
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
sgrow787
Posts: 275
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 3:09 pm

flybucky wrote:
aljrooney wrote:
I did a quick search....Anyone seen this?
http://www.youtube.com/watch?v=HWZhbsGHBss
FAA grounded Cirrus Vision Jets
Some similarities and issue with AOA installation?

These are not the same AOA sensors, but it does sound like an analogous situation.

An AOA failure resulted in erroneous AOA data, which triggered an automatic nose down by the computer system (stall warning and protection system (SWPS) or electronic stability and protection system (ESP)). The root cause was "two set screws that secure the potentiometer shaft to the AOA vane shaft can feature “improper torqueing and no application of thread locker [loctite] to secure the two set screws.”"

https://www.aviationtoday.com/2019/04/1 ... incidents/


I think the more accurate statement is "the probable root cause...":

Aerosonic, the company that manufactures the AOA sensors for the SF50, believes that the probable root cause of the three different incidents resulted from AOA sensor malfunction due to a “quality escape” during assembly. Specifically, the two set screws that secure the potentiometer shaft to the AOA vane shaft can feature “improper torqueing and no application of thread locker to secure the two set screws.”


Personally, it wouldn't surprise me if this is nothing but more PR response from Foeing (FAA/Boeing). "Hey look, Boeing's not the only one with AOA sensor issues, not the only one with systems that push the nose down."
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
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ssteve
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 3:12 pm

sgrow787 wrote:
Personally, it wouldn't surprise me if this is nothing but more PR response from Foeing (FAA/Boeing). "Hey look, Boeing's not the only one with AOA sensor issues, not the only one with systems that push the nose down."


The FAA is conspiring with Boeing to do it's job? Does that dovetail into QAnon somehow, too?
 
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par13del
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 3:18 pm

sgrow787 wrote:
Personally, it wouldn't surprise me if this is nothing but more PR response from Foeing (FAA/Boeing). "Hey look, Boeing's not the only one with AOA sensor issues, not the only one with systems that push the nose down."

Boeing and the FAA PR cannot make a company liable for damages, if the device is / was faulty, the manufacturer will bear legal and financial liability, how quick we forget that the USA is a country of liability, guess we easily forget the ambulance chaser.
Boeing and the FAA will be held responsible for whatever laws, rules and or regulations that they break or have broken, the USA has too many media houses, Benedict Arnolds and whistle blowers to hide a conspiracy.
Look at how much MCAS stuff has come out inspite of it not being included in some documentation, it was already out there.
 
WIederling
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 3:37 pm

zeke wrote:
What you are posting simply is not true. Any changes to the MAX from the NG is certified to FAR standards at the date when the FAA accepted their application.

It would meet the current stability requirements.


Would be interesting to know what has been defined as "not changed" from the NG ( resp. Classic, Jurassic ) to the MAX:
This presents the constraints that MCAS was intended to wiggle past while keeping the pretense.
Murphy is an optimist
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 4:32 pm

XRAYretired wrote:
The writings you have attributed to me above are not mine, although I do not necessarily disagree with them.

Oops, very sorry for my confusion. Please forgive me, :white:
sgrow787 wrote:
I recognise the statements regarding AOA analogue being separately routed to ADIRU and SYMD and it is likely that SYMD initiates the Stick Shaker.

The problem I still have in accepting 'not ADIRU' position is why is the affected side IAS is low, when I am being told that AOA high should result in AIS high as well?

Conversely, I have a problem accepting the 'it is AIDRU' position whist I do not have any information identifying what ADIRU problem or other source data used by ADIRU would result in AIS low, Altitude low and AOA high? I am conscious that all three begin at the same time stamp (but could just be related to WOW FALSE).
Ray.

Trying to learn about the AoA/IAS argument, I share my understanding from this document page 1 for the definition and page 7 for the Variation of Verror with AOA graph:
https://www.nal.res.in/FullPapers/P8-Po ... 0using.pdf
Verror = ((Vmeasured-Vfree)*100)/Vfree = 100*(Vmeasured/Vfree-1) => Vfree = Vmeasured/(Verror/100+1)
Assuming AoA indicate a +20° offset but that the Pitot tube angle of attack is still 0°, the Vmeasured will stay the same but the Verror used for the correction will increase from -3.5% to well over 3%. The Vfree computed with the wrong Verror caused by the +20° AoA offset will DECREASE.
For example:
Vmeasured = 300 and AoA = 0° => Verror = -3.5% => Vfree = 300/(-3.5/100+1) = 310.88
Vmeasured = 300 and AoA = 20° => Verror = 3% => Vfree = 300/(3/100+1) = 291.26
Last edited by PixelFlight on Sat Apr 27, 2019 4:48 pm, edited 1 time in total.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 4:46 pm

sgrow787 wrote:
(I would have added the link from ADIRU to SMYD, since the system block diagram shows that connection, and because the SMYD needs airspeed to make it's decision on stick shaker.)

There a lot of others connections, but I deliberately simplified to only show how the left AoA value flow and how the related consequences are send to the FDR. The SMYD don't use the AoA value from any ADIRUs in that schematic:
Image
 
XRAYretired
Posts: 634
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Apr 27, 2019 5:47 pm

PixelFlight wrote:
XRAYretired wrote:
The writings you have attributed to me above are not mine, although I do not necessarily disagree with them.

Oops, very sorry for my confusion. Please forgive me, :white:
sgrow787 wrote:
I recognise the statements regarding AOA analogue being separately routed to ADIRU and SYMD and it is likely that SYMD initiates the Stick Shaker.

The problem I still have in accepting 'not ADIRU' position is why is the affected side IAS is low, when I am being told that AOA high should result in AIS high as well?

Conversely, I have a problem accepting the 'it is AIDRU' position whist I do not have any information identifying what ADIRU problem or other source data used by ADIRU would result in AIS low, Altitude low and AOA high? I am conscious that all three begin at the same time stamp (but could just be related to WOW FALSE).
Ray.

Trying to learn about the AoA/IAS argument, I share my understanding from this document page 1 for the definition and page 7 for the Variation of Verror with AOA graph:
https://www.nal.res.in/FullPapers/P8-Po ... 0using.pdf
Verror = ((Vmeasured-Vfree)*100)/Vfree = 100*(Vmeasured/Vfree-1) => Vfree = Vmeasured/(Verror/100+1)
Assuming AoA indicate a +20° offset but that the Pitot tube angle of attack is still 0°, the Vmeasured will stay t. he same but the Verror used for the correction will increase from -3.5% to well over 3%. The Vfree computed with the wrong Verror caused by the +20° AoA offset will DECREASE.
For example:
Vmeasured = 300 and AoA = 0° => Verror = -3.5% => Vfree = 300/(-3.5/100+1) = 310.88
Vmeasured = 300 and AoA = 20° => Verror = 3% => Vfree = 300/(3/100+1) = 291.26


Excellent. Thank you. We duffers need to be lead by the nose sometimes.

I'm on board and everything seems to support loss of the AOA vane probably due to bird strike (which is where we started I think). Looking at JT043/JT610, we have sufficient similarity so I'm back to the opinion that we are looking at AOA MRO or installation fault (remembering that the pre-JT043 AOA has been reported defective by Indonesian investigation team and pre-JT043 maintenance reports looks significantly different).

Ray
 
Saintor
Posts: 29
Joined: Wed Mar 13, 2019 10:35 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 28, 2019 1:40 am

sgrow787 wrote:

https://www.aviationtoday.com/2019/04/1 ... incidents/

I think the more accurate statement is "the probable root cause...":





Does 'root cause' = 'determinant cause' to you?

Unsure about JT610, but I think that ET302 flight should have been saved. I understand some procedures appeared confusing, yet no reason why they were at 94% trust/340+ knots at that altitude.

And Boeing was clearly in the wrong relying on a single sensor feeding MCAS.

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