xmp125a
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:30 am

PixelFlight wrote:
MD80Ttail wrote:
xmp125a wrote:

You would tear off the flaps IF you could even extend them at unsafe aerodynamic pressure (I would assume system does not allow that). Even worse, you would partially tear of only one of them, sending plane into unrecoverable spin and end up as pile of smoking debris on the ground, with investigators wondering what the hell were you doing when extending flaps at 300kts, let alone 400kts.

http://www.b737.org.uk/flapspeedschedule.htm¡

Are you really an airline pilot?!


It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.


But let's not forget that pilots did not have the luxury of reading their own accident report and going from there. If this procedure really works then this is another damning evidence against Boeing who had months after lion air to design AND test emergency procedures before Ethiopian went down.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:31 am

kalvado wrote:
PixelFlight wrote:
MD80Ttail wrote:


Wow. Can’t believe I have to explain in such detail. The Mcas issue started when flaps were retracted. One of the basic rules of flying is if you take an action and the plane doesn’t like it undo said action. The IAS problems started immediately after take off and the MCAS problems where flaps were retracted. I would have immediately redeployed the flaps after retracting them and having an issue -or- would have never retracted them in the beginning in this situation knowing it would engage MCAS. Which they should have known after the Lion crash. Then fly pitch and power for said configuration. Before the flaps “rip” off you will get some nice buffeting as a warning btw.

It’s frustrating today every little detail has to be explained. One would think the premise is easy to understand.

It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.

Flaps extension can produce additional nose down pitch, extra forces on a coloumn and stabilizer. That is when there is another pitch down problem. If blowback is the thing, it will make things worse.
Is it bad enough of effect?

The proposed procedure is not to just "flaps not up" to disable MCAS but also "manual electric stab trim". Yes the "flaps not up" is not the ideal configuration, but it that really as lethal thread that prevent the aircraft to return and landing ? The Aviation Herald routinely have entries about flaps problems and obviously the pilots are very capable of handling that kind of situation.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:35 am

xmp125a wrote:
PixelFlight wrote:
MD80Ttail wrote:

It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.


But let's not forget that pilots did not have the luxury of reading their own accident report and going from there. If this procedure really works then this is another damning evidence against Boeing who had months after lion air to design AND test emergency procedures before Ethiopian went down.

I think this even more brutal. The EAD 2018-23-51 will certainly become a criminal evidence against Boeing and the FAA. There published a lethal procedure without verification.
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:52 am

mxaxai wrote:
I wonder, though, why MCAS gave one automatic AND input after the trim cut out switches had been flipped, then remained dormant, and only reactivated after (presumably) electric trim had been reactived. Could it be that inputs to the electric trim - either manually on the yoke or from MCAS - were not recorded while electric trim was off (after some initial transition time)?

zeke wrote:
There presently is no direct way to actually turn off MCAS, the only way that I have seen to indirectly turn off MCAS is by selecting flap greater than zero. The AD that has been published just turns off power to the stabilizer, the actual command from the MCAS located in the FCC will continue to tell the aircraft to pitch nose down if the actuation conditions are met. Turning power back on to the stabilizer will enable the MCAS commands to start moving the stabilizer again.

With respect, I believe mxaxai's question is why did MCAS only function once during the period the trim cut out switches were flipped?

With the AoA data consistently off the charts, we should have seen MCAS attempting to move the jackscrew every 15 seconds.

Instead, it operated more like the sentient pilots; it tried once, failed, and then gave up. :scratchchin:

(yes, that is most unfair to the pilots - I was attempting a joke...)

Are there more lines of code buried in the MCAS system, taking it to a different level?

EDIT; I presume there is a function that prevents the motor from operating if the jackscrew is already at the limit of it's travel (which is wasn't in this case), but I also assume that this control is located closer to the motor relay itself.
Nothing to see here; move along please.
 
arcticcruiser
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 12:03 pm

PixelFlight wrote:
MD80Ttail wrote:
xmp125a wrote:

You would tear off the flaps IF you could even extend them at unsafe aerodynamic pressure (I would assume system does not allow that). Even worse, you would partially tear of only one of them, sending plane into unrecoverable spin and end up as pile of smoking debris on the ground, with investigators wondering what the hell were you doing when extending flaps at 300kts, let alone 400kts.

http://www.b737.org.uk/flapspeedschedule.htm¡

Are you really an airline pilot?!



Wow. Can’t believe I have to explain in such detail. The Mcas issue started when flaps were retracted. One of the basic rules of flying is if you take an action and the plane doesn’t like it undo said action. The IAS problems started immediately after take off and the MCAS problems where flaps were retracted. I would have immediately redeployed the flaps after retracting them and having an issue -or- would have never retracted them in the beginning in this situation knowing it would engage MCAS. Which they should have known after the Lion crash. Then fly pitch and power for said configuration. Before the flaps “rip” off you will get some nice buffeting as a warning btw.

It’s frustrating today every little detail has to be explained. One would think the premise is easy to understand.

It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.


What is "manual electric stab trim"? No such thing on the 737 IIRC. Stab trim switches on the yoke = electric stab trim. Manual stab trim = trim wheels. Nothing in between.
 
Some1Somewhere
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 12:22 pm

arcticcruiser wrote:
PixelFlight wrote:
MD80Ttail wrote:


Wow. Can’t believe I have to explain in such detail. The Mcas issue started when flaps were retracted. One of the basic rules of flying is if you take an action and the plane doesn’t like it undo said action. The IAS problems started immediately after take off and the MCAS problems where flaps were retracted. I would have immediately redeployed the flaps after retracting them and having an issue -or- would have never retracted them in the beginning in this situation knowing it would engage MCAS. Which they should have known after the Lion crash. Then fly pitch and power for said configuration. Before the flaps “rip” off you will get some nice buffeting as a warning btw.

It’s frustrating today every little detail has to be explained. One would think the premise is easy to understand.

It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.


What is "manual electric stab trim"? No such thing on the 737 IIRC. Stab trim switches on the yoke = electric stab trim. Manual stab trim = trim wheels. Nothing in between.


I would say "automatic electric stab trim" would be STS or similar; in the sense that it's not directly pilot commanded. Yoke switches = "manual electric stab trim", in the sense that while the electrics is doing the physical work, the pilot said "move the stabiliser".
 
xmp125a
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 12:24 pm

PixelFlight wrote:
xmp125a wrote:
PixelFlight wrote:


But let's not forget that pilots did not have the luxury of reading their own accident report and going from there. If this procedure really works then this is another damning evidence against Boeing who had months after lion air to design AND test emergency procedures before Ethiopian went down.

I think this even more brutal. The EAD 2018-23-51 will certainly become a criminal evidence against Boeing and the FAA. There published a lethal procedure without verification.


It is also conceivable that pilots have been taught to follow the proscribed procedures because everyone assumes that before they are released to pilots they are well rested in simulators or perhaps even in real flight AND that alternatives that pop up in ones brain during emergency were also tested and found to be non effective or even dangerous. That would be my reasoning, but I am not a pilot.

That means even if pilots got the idea "let's put flaps back on", their training would kick in and prevent them from doing unrecommended, possibly untested procedure instead of recently published EAD 2018-23-51 which certainly was imprinted in their mind due to Lion air crash.
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 12:26 pm

morrisond wrote:
flybucky wrote:
We know that FO did not try Electric Trim during that time because the FDR Electric Trim Command showed no activity during that time (the FDR data would have shown Electric Trim Command even if the Stab Trim was cutout).
I thought the same thing - but Would it have shown it though if the power was cut-off? MCAS shows when the trim was cut-off probably because it is powered on different circuit?

Of all the various things you have posted, this is possibly the most useful. :lol:

Flybucky states that the FDR trace would show all thumb switch commands even after the power was cut off.
Likewise I have assumed this was the case.
And the fact that MCAS tried to function, and was recorded as such on the FDR despite it also being disabled by the cut-out switches, seemed to corroborate this.

However... without access to the wiring diagrams, your question is 100% valid.

I can see an argument for isolating the power upstream of the thumb switches, to cover the possibility of the switch itself failing, and possibly supplying live power to the framework of the control column (which I'm guessing is earthed/double insulated).

The only resource I could come up with was JT043, the Lion Air flight that survived after successfully operating stab trim cut out.

And as soon as I started looking at that, alarm bells rang.
I might need some time to think this through....
Nothing to see here; move along please.
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 12:38 pm

arcticcruiser wrote:
What is "manual electric stab trim"? No such thing on the 737 IIRC. Stab trim switches on the yoke = electric stab trim. Manual stab trim = trim wheels. Nothing in between.

I suggest you have words with both the Indonesian and Ethiopian AAIB because they both use the term in respect of FDR data traces. :lol:

For JT610 there is either "Trim Manual" or Trim Automatic", and they are definitely not referring to the trim wheel in either case.

For ET302 they specifically identify one spike on the graph as a "Manual (Electric) Trim Command"

It is possible that both organisations have got it wrong, and that you are the only person to spot it so far..

Unlike many on these forums, I don't trust my memory to be 100% correct.

The information is out there if you can be bothered.
Nothing to see here; move along please.
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 1:00 pm

zeke wrote:
mxaxai wrote:
I wonder, though, why MCAS gave one automatic AND input after the trim cut out switches had been flipped, then remained dormant, and only reactivated after (presumably) electric trim had been reactived. Could it be that inputs to the electric trim - either manually on the yoke or from MCAS - were not recorded while electric trim was off (after some initial transition time)?

There presently is no direct way to actually turn off MCAS, the only way that I have seen to indirectly turn off MCAS is by selecting flap greater than zero. The AD that has been published just turns off power to the stabilizer, the actual command from the MCAS located in the FCC will continue to tell the aircraft to pitch nose down if the actuation conditions are met. Turning power back on to the stabilizer will enable the MCAS commands to start moving the stabilizer again.

Compare the FDR data for JT043 - the Lion Air flight that survived after correctly hitting the stab trim cut out switches.

The exact point at which the switches were thrown is not specified, but either side of the data line at 14:33:54 there are indications of MCAS trim down, manual electric trim up, and finally manual trim wheel up (inferred).
This was followed by 60 minutes of level flight, with stable trim conditions, and no MCAS input ! (and no electric thumb switch operation either)

During the 30 min descent from altitude, MCAS attempted to operate sporadically (four times) with no effect. Another oddity.
Meanwhile the actual pitch trim was controlled manually (by trim wheel).

And they all lived happily ever after. :D

So to a large extent we have the same pattern; MCAS predominantly sulked in the background when we might have expected it to function hundreds of times at 15 sec intervals.
Nothing to see here; move along please.
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 1:24 pm

SheikhDjibouti wrote:

During the 30 min descent from altitude, MCAS attempted to operate sporadically (four times) with no effect. Another oddity.

Those don't have to be MCAS. Could be STS. Especially since it looks as though the last one came after flap extension.
Phrogs Phorever
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 1:48 pm

dragon6172 wrote:
SheikhDjibouti wrote:
During the 30 min descent from altitude, MCAS attempted to operate sporadically (four times) with no effect. Another oddity.

Those don't have to be MCAS. Could be STS. Especially since it looks as though the last one came after flap extension.

Thx. I'm here to learn, so tell me more.

The earlier 2-3 cycles display no particular logic.
Nothing obvious occurred immediately before to obviously cause STS to function
Nothing significantly different happened following (because electric trim was disabled)
So whatever prompted STS to operate, why wasn't it 20-30 back-to-back cycles of STS?
(I admit I don't know which parameters cause STS to function)

The second pair of automatic trim attempts do indeed coincide with minimal flaps (5 deg, or whatever it represents) and a tiny corresponding movement on both AoA sensors

p.s. all the above is re JT043
Nothing to see here; move along please.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 2:10 pm

dragon6172 wrote:
SheikhDjibouti wrote:

During the 30 min descent from altitude, MCAS attempted to operate sporadically (four times) with no effect. Another oddity.

Those don't have to be MCAS. Could be STS. Especially since it looks as though the last one came after flap extension.

I think we can deduce from the FDR alalyses that Trim Switch in Normal position is a pre-requsite to MCAS becoming active (i.e. is inhibited in Cut-Out the same as with Flaps Down), so no command is given. It is then clear for ET302 that the Trim switches are in Normal initiating MCAS shortly before TRIM switches are moved to CUT-OUT so MCAS completes it 10 sec cycle but with TRIM now in CUT-OUT there is no effect on pitch.

I suspect a similar situation exists for manual electrical trim via the thumb switch. In that, if Trim is in CUT-OUT, thumb switch is inhibited so no command is seen.

Is this the situation for STS? Possibly not if the auto trim commands in the FDRs with Trim switches in CUT-OUT are STS set. Or could the traces be gliches?

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

Sun Apr 07, 2019 2:24 pm

arcticcruiser wrote:
PixelFlight wrote:
MD80Ttail wrote:


Wow. Can’t believe I have to explain in such detail. The Mcas issue started when flaps were retracted. One of the basic rules of flying is if you take an action and the plane doesn’t like it undo said action. The IAS problems started immediately after take off and the MCAS problems where flaps were retracted. I would have immediately redeployed the flaps after retracting them and having an issue -or- would have never retracted them in the beginning in this situation knowing it would engage MCAS. Which they should have known after the Lion crash. Then fly pitch and power for said configuration. Before the flaps “rip” off you will get some nice buffeting as a warning btw.

It’s frustrating today every little detail has to be explained. One would think the premise is easy to understand.

It's now clear that the procedure you propose (flaps not up + manual electric stab trim) is by far superior to anything Boeing have produced yet in case of AOA disagree on a 737 MAX with MCAS v1.


What is "manual electric stab trim"? No such thing on the 737 IIRC. Stab trim switches on the yoke = electric stab trim. Manual stab trim = trim wheels. Nothing in between.

I mean "Stab trim switches on the yoke = electric stab trim". Sorry for the wording.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 2:47 pm

SheikhDjibouti wrote:
morrisond wrote:
flybucky wrote:
We know that FO did not try Electric Trim during that time because the FDR Electric Trim Command showed no activity during that time (the FDR data would have shown Electric Trim Command even if the Stab Trim was cutout).
I thought the same thing - but Would it have shown it though if the power was cut-off? MCAS shows when the trim was cut-off probably because it is powered on different circuit?

Of all the various things you have posted, this is possibly the most useful. :lol:

Flybucky states that the FDR trace would show all thumb switch commands even after the power was cut off.
Likewise I have assumed this was the case.
And the fact that MCAS tried to function, and was recorded as such on the FDR despite it also being disabled by the cut-out switches, seemed to corroborate this.

However... without access to the wiring diagrams, your question is 100% valid.

From the published schematic of the B737 MAX it's absolutely clear that both "F/O STAB TRIM SW" and "CAPT STAB TRIM SW" are _ONLY_ powered by the exactly _SAME_ "STAB TRIM CONTROL" 28V signal that energize the "R64 STAB TRIM CONT RELAY". There is obviously _NO_WAY_ to record action of the "F/O STAB TRIM SW" or "CAPT STAB TRIM SW" if the "STAB TRIM CUTOUT SW" are not _BOTH_ on the "NORM" position.
Image
 
ikramerica
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 2:58 pm

MSPNWA wrote:
Jetty wrote:
It’s not hard in good conditions. But in bad conditions it can be, as is shown by the ET pilot not being able to get it moving.


More completely unknown details stated as known fact. We have no proof they even touched the trim wheels, let alone couldn't turn them.

Sadly I think we will find out that the near zero time FO only tried his electric switches and didn’t try the manual wheel, or didn’t realize how many rotations it takes to move it. The decision to reengage electric trim was counter to procedure and likely fatal.

The odds of the AoA sensors failing AND the trim crank failing are astronomical.
Of all the things to worry about... the Wookie has no pants.
 
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 3:31 pm

mandala499 wrote:
By the way, anyone tried to pulling the manual trim up while having 1/2 to 2/3 aft column input, while flying at Vmo, in the 737NG sim?


scbriml wrote:
Even without knowing if they attempted to use the trim wheel, we have evidence from Bjorn at Leeham supporting the fact that the trim wheel becomes incredibly heavy to turn at high aerodynamic loads. Even more so when pulling back on the yoke for all you're worth.


MentourPilot had recreated the ET302 trim conditions (ie close at Vmo, heavy control column) in the 737 NG sim. Apparently he needed to have both arms around the column to maintain the desired pull force on the control column, and found that the trim wheel was extremely hard to be turned. Unfortunately, he removed his video the same day.
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

So yes, it was tried in the 737NG sim, and confirmed the theories in this respect.
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mandala499
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 3:44 pm

PW100 wrote:
MentourPilot had recreated the ET302 trim conditions (ie close at Vmo, heavy control column) in the 737 NG sim. Apparently he needed to have both arms around the column to maintain the desired pull force on the control column, and found that the trim wheel was extremely hard to be turned. Unfortunately, he removed his video the same day.
Here he explains why it was removed, but confirms his findings:

I might try that myself on the 737NG simulator... just to see it for myself... But I'd probably just limit it to the trim behaviour and column forces...
But then...
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
mxaxai
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 4:29 pm

SheikhDjibouti wrote:
With respect, I believe mxaxai's question is why did MCAS only function once during the period the trim cut out switches were flipped?

With the AoA data consistently off the charts, we should have seen MCAS attempting to move the jackscrew every 15 seconds.

Instead, it operated more like the sentient pilots; it tried once, failed, and then gave up. :scratchchin:

(yes, that is most unfair to the pilots - I was attempting a joke...)

Exactly.

However, this sounds like a potential explanation:
XRAYretired wrote:
I think we can deduce from the FDR alalyses that Trim Switch in Normal position is a pre-requsite to MCAS becoming active (i.e. is inhibited in Cut-Out the same as with Flaps Down), so no command is given. It is then clear for ET302 that the Trim switches are in Normal initiating MCAS shortly before TRIM switches are moved to CUT-OUT so MCAS completes it 10 sec cycle but with TRIM now in CUT-OUT there is no effect on pitch.

Ray

There were only 5 seconds between the end of the ANU trim and the next MCAS cycle. Certainly possible that the trim was still powered, briefly. If the system only checks for electric power at the beginning of each cycle, it would command AND trim for the full duration even if power is lost in between. Of course nothing happens, because the trim cannot execute the command without power.

ikramerica wrote:
Sadly I think we will find out that the near zero time FO only tried his electric switches and didn’t try the manual wheel, or didn’t realize how many rotations it takes to move it. The decision to reengage electric trim was counter to procedure and likely fatal.

The very experienced captain called out "pitch is not enough". I would not be surprised if he was the one to reengage electric trim, particularly after he asked the FO to "pitch up together", which may have allowed him to take one hand off the yoke. We'll probably never know for sure (OT: a video camera could help reconstruct such interactions).
 
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 5:01 pm

ikramerica wrote:
MSPNWA wrote:
Jetty wrote:
It’s not hard in good conditions. But in bad conditions it can be, as is shown by the ET pilot not being able to get it moving.


More completely unknown details stated as known fact. We have no proof they even touched the trim wheels, let alone couldn't turn them.

Sadly I think we will find out that the near zero time FO only tried his electric switches and didn’t try the manual wheel, or didn’t realize how many rotations it takes to move it. The decision to reengage electric trim was counter to procedure and likely fatal.

The odds of the AoA sensors failing AND the trim crank failing are astronomical.

Unless these factors are linked (through MCAS), and trim crack failed due to extreme aerodynamic loading. If that was indeed the case, we don't know at this point. But there are certainly indications to such effect:
1) Extreme airspeed, close to, or even exceeding Vmo;
2) Significant stabilizer pitch trim (AND);
3) Significant elevator displacement (ANU);
4) Leeham suggesting that at the above combination of factors would result in inability to turn the trim wheel manually. This was confirmed by sim experiment by Mentour Pilot.

https://leehamnews.com/2019/04/05/bjorns-corner-et302-crash-report-the-first-analysis/
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PlanesNTrains
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 5:12 pm

SomebodyInTLS wrote:
MD80Ttail wrote:
I have stated this before but no one has discussed.....if I was in the ET cockpit...and I had considered this before the ET crash after learning from the lion accident.....I would have lowered flaps to disable the MCAS while still allowing use of the electric trim. Thoughts?


In overspeed...


I’m reminded of my now- father-in-law, who I love and respect in many ways, but who is deeply flawed in believing that he is always right and knows what’s best. Case in point: In 1991, my step-dad was killed in a head-on crash with a drunk driver. The next day, my then-fiancé and I stopped by her parents house to share the news. Her father replied “Oh, I would’ve been looking for someplace to go”, implying that my dead step-dad just didn’t have the elevated driving skills needed to safely evade the collision. Never mind it happened at a combined 90mph on a left hand curve with no median and the oncoming vehicle crossed over literally a moment before the collision.

As here, some people think they’d “xyz” because they’re just that smart/skilled/capable/aware - fill in the blank. They make these pronouncements standing g on the graves of the “responsible” without even having the full picture or allowing for the human factor.

My FIL is 83 and even his family struggles being around him. I can’t imagine why? At least here, we have the foe option.
-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.
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 5:42 pm

SheikhDjibouti wrote:
EDIT; I presume there is a function that prevents the motor from operating if the jackscrew is already at the limit of it's travel (which is wasn't in this case), but I also assume that this control is located closer to the motor relay itself.


IIRC, investigators found the ET stabilizer jack screw, and it was in its full nose down trim position.
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1989worstyear
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 5:48 pm

PixelFlight wrote:
planecane wrote:
Is Airbus management too business based to do the NEO instead of a clean sheet replacement?

The A320 is already a clean sheet design compared to the B737. Changing the engines was more easy for the NEO than for the MAX.


1988 was 31 years ago. I think you meant to say it's a better platform for re-engining due to having FBW from the start.
Stuck at age 15 thanks to the certification date of the A320-200 and my parents' decision to postpone having a kid by 3 years. At least there's Dignitas...
 
smartplane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 6:33 pm

zeke wrote:
mxaxai wrote:
I wonder, though, why MCAS gave one automatic AND input after the trim cut out switches had been flipped, then remained dormant, and only reactivated after (presumably) electric trim had been reactived. Could it be that inputs to the electric trim - either manually on the yoke or from MCAS - were not recorded while electric trim was off (after some initial transition time)?


There presently is no direct way to actually turn off MCAS, the only way that I have seen to indirectly turn off MCAS is by selecting flap greater than zero. The AD that has been published just turns off power to the stabilizer, the actual command from the MCAS located in the FCC will continue to tell the aircraft to pitch nose down if the actuation conditions are met. Turning power back on to the stabilizer will enable the MCAS commands to start moving the stabilizer again.

And is flap setting greater than zero overridden in certain conditions?

When the stabiliser is powered off, does MCAS accumulate commands, so when the stabiliser is powered back on, the magnitude of MCAS commands is greater than usual?
 
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7BOEING7
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 6:40 pm

flybucky wrote:
Here's a video of pilots demonstrating manual wheel trim in a parked 737-800 NG. They set the trim to 0 units (full nose down) and attempted the manual wheel to trim back to normal 5 units.

That was in a parked 737 with no aerodynamic forces on the stabilizer. The FO struggled and was only able to trim 1 unit in 1 minute, and was exhausted afterwards. Using the left hand may have been a factor. There have been several experts that have said that the aerodynamic forces on an out-of-trim stabilizer when the elevator is up (which it was, because the FDR Control Column Position was 5-10º nose up for most of the flight) at high speed would likely make it impossible for the manual wheel to be able to trim up.

Even the Captain in the demo, who had no problems turning the manual trim wheel, took 30 seconds to trim back to normal 5 units. According to the Preliminary Report graph, ET302 crashed ~20 seconds after the final MCAS command.


Having used the manual trim wheels on the ground hundreds of times and watched other pilots (male and female, left hand and right hand), the Captain is much more representative of reality -- 30 seconds might be a little long for the speed I've generally observed myself and others doing. The FO on the other hand is either faking it or is so weak/uncoordinated he has no business in an airplane.

Having also operated the manual trim wheels in flight at various altitudes from 15,000 ft to FL350 at normal operating speeds the loads i observed were not much different than on the ground.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 7:16 pm

Jetty wrote:
mjoelnir wrote:
speedking wrote:
I wonder why Boeing designed the Final Gatekeeper, the manual trim wheel system, so poorly that it is impossible to use in the whole flight envelope and a bit more to really make sure that you can save the plane if all automation and electrical system fails?
What if you are in the high end of the envelope and you get a real trim runaway and cannot use the electric trim to bring the trim back to neutral before hitting the cut off switches?
Now the system seems to be like a Russian-made anal vibrator. Doesn't fit in and doesn't vibrate.


Perhaps 60 years ago they did not know better? And grandfathering something is more important than that things actually work?

I also do not understand how Boeing got away with making the wheels smaller, long before the MAX, and so still more difficult to use it.

Exactly. Especially as there are many more female pilots flying. Nothing against that, but on average their upper body strength is only about half that of males. If anything, they should have made the wheel twice as big. The 737 doesn't only need skillful pilots, as it is it needs strong pilots as well.


Or maybe an electric boost motor on the manual trim wheel?

"If a problem comes along ... you must kludge it..... kludge it good!"
(Apologies to "Devo.")
:stirthepot:
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 7:19 pm

RickNRoll wrote:
Jetty wrote:
mjoelnir wrote:

Perhaps 60 years ago they did not know better? And grandfathering something is more important than that things actually work?

I also do not understand how Boeing got away with making the wheels smaller, long before the MAX, and so still more difficult to use it.

Exactly. Especially as there are many more female pilots flying. Nothing against that, but on average their upper body strength is only about half that of males. If anything, they should have made the wheel twice as big. The 737 doesn't only need skillful pilots, as it is it needs strong pilots as well.


The NG trim wheels were made smaller than the Classic trim wheels to fit the new, larger instrement panel. When electric trim was added a damper had to be placed on the manual trim to stop springback. Both changes added to the physical load on the pilot trying to manually trim.


:checkmark:
"One thing leads to another."
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 7:26 pm

Elshad wrote:
Would a small increase in horizontal stabiliser area make MCAS redundant? Obviously all frames would need to be retrofitted at great cost but it would be a real solution as opposed to an MCAS patch.


:checkmark:

I'm with you - in favor of an expensive hardware redesign, rather than an inexpensive sofware redesign. "There's never time to do the job correctly the first time, but always time to redo it....."
If Boeing truly wants to save the long-term reputation of the aircraft, it seems to me that a definitive hardware fix goes a lot farther in rebuilding confidence than a software "kludge."

Just my opinion, but I would rather see Boeing think long-term, rather than short-term.

The first rule of holes is to stop digging.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 8:05 pm

Can someone explain to me what is the "F/C COL CUTOUT SW MOD" ?

It look like it have 2 switches "COL AFT" (?) and "COL FWD" (?). I suspect that either of those switches can cut automatic STAB TRIM signals from the FCC, so maybe from the MCAS too, without disabling the "Stab trim switches on the yoke = electric stab trim".
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 8:15 pm

PixelFlight wrote:
Can someone explain to me what is the "F/C COL CUTOUT SW MOD" ?

It look like it have 2 switches "COL AFT" (?) and "COL FWD" (?). I suspect that either of those switches can cut automatic STAB TRIM signals from the FCC, so maybe from the MCAS too, without disabling the "Stab trim switches on the yoke = electric stab trim".


If the trim is running forward and you pull the column aft or if you're trimming forward and pull the column aft the trim stops -- and vice versa -- except if MCAS is functioning.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:04 pm

PW100 wrote:
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

Thanks for that link regarding Mentour Pilot's decision to pull his video. But I did not have time to watch the 50 minute (!) video. Does someone have a summary? I only watched the first few minutes, where he said he pulled the video purely on his own decision, not due to any pressure from his company, Boeing, etc.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:12 pm

7BOEING7 wrote:
PixelFlight wrote:
Can someone explain to me what is the "F/C COL CUTOUT SW MOD" ?

It look like it have 2 switches "COL AFT" (?) and "COL FWD" (?). I suspect that either of those switches can cut automatic STAB TRIM signals from the FCC, so maybe from the MCAS too, without disabling the "Stab trim switches on the yoke = electric stab trim".


If the trim is running forward and you pull the column aft or if you're trimming forward and pull the column aft the trim stops -- and vice versa -- except if MCAS is functioning.

Yes. According to Peter Lemme, the Column Aft/Fwd Cutout switches were for the 737 NG to cutout Speed Trim with the yoke. However, they do not cutout MCAS.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:14 pm

7BOEING7 wrote:
PixelFlight wrote:
Can someone explain to me what is the "F/C COL CUTOUT SW MOD" ?

It look like it have 2 switches "COL AFT" (?) and "COL FWD" (?). I suspect that either of those switches can cut automatic STAB TRIM signals from the FCC, so maybe from the MCAS too, without disabling the "Stab trim switches on the yoke = electric stab trim".


If the trim is running forward and you pull the column aft or if you're trimming forward and pull the column aft the trim stops -- and vice versa -- except if MCAS is functioning.

Thanks :-)
Something strange. The two signals coming from the FCC to the "F/O COL CUTOUT SW MOD" end to the "A/P ENABLE SPEED & DIRECTION" after passing through the "NOT UP" "S144 STAB NODE UP LIMIT SW" for one signal and through the "NOT DOWN" "S145 STAB NODE DOWN LIMIT SW". So it's clear that those two signals are the "STAB TRIM UP" and "STAB TRIM DOWN" signals from the FCC, even if there names are not on the schematic. But there is no similar signal for the MCAS command. As you said, the column didn't cut the MCAS so we are certain that the 2 signals from the FCC to the ELECTRIC STAB TRIM MOTOR don't carry the MCAS signals. But there are only 2 signals that pass through the "NOT DOWN" "S145 STAB NOSE DOWN LIMIT SW", the one from the "STAB TRIM SW" on the yoke and the other from the FCC. My conclusion is that the MCAS send command by a completely different circuit not show in that schematic.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:17 pm

flybucky wrote:
PW100 wrote:
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

Thanks for that link regarding Mentour Pilot's decision to pull his video. But I did not have time to watch the 50 minute (!) video. Does someone have a summary? I only watched the first few minutes, where he said he pulled the video purely on his own decision, not due to any pressure from his company, Boeing, etc.

Interesting
Last edited by smartplane on Sun Apr 07, 2019 9:21 pm, edited 1 time in total.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:20 pm

arcticcruiser wrote:
What is "manual electric stab trim"? No such thing on the 737 IIRC. Stab trim switches on the yoke = electric stab trim. Manual stab trim = trim wheels. Nothing in between.

This is an unfortunate terminology that leads to ambiguity, but there is such a thing as "manual electric stab trim". The FDR has a data field called "Trim Up-Man" and "Trim Down-Man", but it is referring to the Electric Trim, not the Manual Wheel Trim. It is also labeled as "Manual (Electric) Trim Command" in the Preliminary Report graph.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:34 pm

morrisond wrote:
I thought the same thing - but Would it have shown it though if the power was cut-off? MCAS shows when the trim was cut-off probably because it is powered on different circuit?

SheikhDjibouti wrote:
However... without access to the wiring diagrams, your question is 100% valid.

I agree that this is a valid question. It is entirely possible that the FDR records the Electric Trim Command after the Stab Trim Cutout, which would be very unfortunate (since ideally we want to see what the pilot's actions were). Ideally, the FDR would be recording Electric Trim Command before Stab Trim Cutout, and also recording the Stab Trim Cutout position.

The MCAS command is also very ambiguous on the FDR graph as well. There is no specific MCAS command signal on the graph. It is "Automatic Trim Command", which includes STS and MCAS. There is 1 MCAS command which did not result in actual Pitch Trim change, leading to the conclusion that the FDR is recording MCAS command before Stab Trim Cutout. However, then why were there no MCAS commands for the next 3 minutes, even though all the MCAS conditions were met (flaps up, AP off, excessive AOA input)?
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 9:53 pm

flybucky wrote:
morrisond wrote:
I thought the same thing - but Would it have shown it though if the power was cut-off? MCAS shows when the trim was cut-off probably because it is powered on different circuit?

SheikhDjibouti wrote:
However... without access to the wiring diagrams, your question is 100% valid.

I agree that this is a valid question. It is entirely possible that the FDR records the Electric Trim Command after the Stab Trim Cutout, which would be very unfortunate (since ideally we want to see what the pilot's actions were). Ideally, the FDR would be recording Electric Trim Command before Stab Trim Cutout, and also recording the Stab Trim Cutout position.

The MCAS command is also very ambiguous on the FDR graph as well. There is no specific MCAS command signal on the graph. It is "Automatic Trim Command", which includes STS and MCAS. There is 1 MCAS command which did not result in actual Pitch Trim change, leading to the conclusion that the FDR is recording MCAS command before Stab Trim Cutout. However, then why were there no MCAS commands for the next 3 minutes, even though all the MCAS conditions were met (flaps up, AP off, excessive AOA input)?

As discussed up thread, have a read back before posting, It can be deduced from the FDR analyses that MCAS conditions likely include TRIM NORMAL/CUT-OUT = NORMAL. Explains the question marks. It is likely that Trim Manual Electric (Thumb Switch) also includes this pre-requisite, so no command is generated from MCAS or Thumb Switch if TRIM SWICHES are in CUT-OUT, so nothing to record in FDR. It would be done in software.

Ray
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 10:11 pm

flybucky wrote:
morrisond wrote:
I thought the same thing - but Would it have shown it though if the power was cut-off? MCAS shows when the trim was cut-off probably because it is powered on different circuit?

SheikhDjibouti wrote:
However... without access to the wiring diagrams, your question is 100% valid.

I agree that this is a valid question. It is entirely possible that the FDR records the Electric Trim Command after the Stab Trim Cutout, which would be very unfortunate (since ideally we want to see what the pilot's actions were). Ideally, the FDR would be recording Electric Trim Command before Stab Trim Cutout, and also recording the Stab Trim Cutout position.

The MCAS command is also very ambiguous on the FDR graph as well. There is no specific MCAS command signal on the graph. It is "Automatic Trim Command", which includes STS and MCAS. There is 1 MCAS command which did not result in actual Pitch Trim change, leading to the conclusion that the FDR is recording MCAS command before Stab Trim Cutout. However, then why were there no MCAS commands for the next 3 minutes, even though all the MCAS conditions were met (flaps up, AP off, excessive AOA input)?



See upthread, post 4663: https://www.airliners.net/forum/viewtopic.php?p=21259805#p21259095

XRAYretired wrote:
I think we can deduce from the FDR alalyses that Trim Switch in Normal position is a pre-requsite to MCAS becoming active (i.e. is inhibited in Cut-Out the same as with Flaps Down), so no command is given. It is then clear for ET302 that the Trim switches are in Normal initiating MCAS shortly before TRIM switches are moved to CUT-OUT so MCAS completes it 10 sec cycle but with TRIM now in CUT-OUT there is no effect on pitch.

I suspect a similar situation exists for manual electrical trim via the thumb switch. In that, if Trim is in CUT-OUT, thumb switch is inhibited so no command is seen.

Is this the situation for STS? Possibly not if the auto trim commands in the FDRs with Trim switches in CUT-OUT are STS set. Or could the traces be gliches?

Ray



Edit: and Ray himself beat me to it . . .
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:03 pm

XRAYretired wrote:
As discussed up thread, have a read back before posting, It can be deduced from the FDR analyses that MCAS conditions likely include TRIM NORMAL/CUT-OUT = NORMAL. Explains the question marks. It is likely that Trim Manual Electric (Thumb Switch) also includes this pre-requisite, so no command is generated from MCAS or Thumb Switch if TRIM SWICHES are in CUT-OUT, so nothing to record in FDR. It would be done in software.

To be precise with the schematic, we don't know if the MCAS command was generated or not while the STAB TRIM CUTOUT SW = CUTOUT, but for sure we know from the schematic that the ELECTRIC STAB TRIM MOTOR is not powered anymore in this case. So regardless if the MCAS command is generated or not, that command can't have any effect on the stab trim motor.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:48 pm

PixelFlight wrote:
My conclusion is that the MCAS send command by a completely different circuit not show in that schematic.

MCAS comes from the FCC. Two things move the stab trim electrically, the column switches and the FCC. The FCC includes autopilot, STS, and MCAS
Phrogs Phorever
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 07, 2019 11:49 pm

flybucky wrote:
PW100 wrote:
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

Thanks for that link regarding Mentour Pilot's decision to pull his video. But I did not have time to watch the 50 minute (!) video. Does someone have a summary? I only watched the first few minutes, where he said he pulled the video purely on his own decision, not due to any pressure from his company, Boeing, etc.


I watched the original sim session that was being pulled and also was smart enough to save the video as well...

The original sim session transcript [C=CAPT; F=FO]:
C: We have an IAS disagree.
C: So, IAS disagree memory items.
F: Autopilot if engaged, disengage.
C: Disengaged!
F: Autothrottle if engaged, disengage.
C: Disengaged!
F: Flight directors - Both up
F: With flaps up established a flight path 4 degrees and 75% N1.
C: So, 75% N1.
F: We have 77, 76,...
C: A little bit less...
F: And, there you go.
C: 4 degrees.
F: 4 degrees.

C: So I am trying to establish this now.
F: Check!
F: We are descending...?
F: We probably... Are you feeling troubled with...
F :Any trouble with the flight control?
C: Yeah, I'm trying to trim it but...
C: It continues to trim against me when I'm trimming
C: So state the malfunction, please.
F: Yeah, this doesn't look right. Looks like uh...
F: How do you feel the stabilizer, the trim system?
F: Can you control it?
C: I'm trimming it. It is responding but...
F: It's a runaway stabilizer, if you agree?
C: For every time that I trim backward, it keeps trimming forward.
F: It's trimming forward. Yeah, it's runaway stabilizer.
C: So, runaway stabilizer memory items...
C: And i'm trying to keep this thing at 4 degrees.
F: Control column, hold firmly.
C: I am... [CAPT is holding the yoke firmly with both hands]
F: Autopilot - if engaged, disengage.
C: It's disengaged.
F: Autothrottle - if engaged, disengage.
C: It's..., if you can disengage it for me, make sure that it's disengaged.
F: It's disengaged.
F: And, do you feel that the failure stop?
F: Negative?
C: No, it's still moving.
F: Stab trim cutoff switches to cutoff.
F: OK. It stops. It looks like it stops.
C: You can see now I'm using almost full back pressure here.
F: Exactly.
C: How many degrees nose down?
F: We have 4 units nose down now
C: 4 units nose down?
F: Yup.
C: OK, I'm struggling.
C: I'm actually using almost my full force to keep the aircraft level here.
F: Do you want me to help you?
C: What I would like to do.
C: Just for the sake of exercise, can you trim this forward? [to simulate MCAS trim AND]
C: See if we can reach even zero nose down.
C: And see if I can even hold it.

[FO is trying to crank the trim wheel to reach zero nose down, simulating MCAS AND]

C: So, now we are doing this just as an exercise!
C: Do not try this at home.
C: This...
C: We are at 300 knots now.
F: I'm fighting.
C: I'm sttrugling to to keep this aircraft flying.
F: My god! [FO surprised at how hard it is to trim further nose down]
C: Yeah, the thing is with higher speed the force on the stabilizer will be higher and higher as well.
C: So it becomes almost impossible to move it.
C: So we are now at about 3 degrees.
F: Yup. [FO still tries to continue trimming nose down, the wheels is so difficult to spin]
C: We're still about 3 degrees away from full nose down trim.
C: And I am using everything that I have. [CAPT still holding on to his yoke with both hands]
F: My God ! [the trim wheel barely move for the down trim]
C: This is realistic guys.
C: This is how much of effort it would take to trim the stabilizer at this kind of speed.
C: Umph... [Capt is still trying to hold on to his yoke with his hands]
C: I'm just in control of it, though. But it's getting harder and harder.
C: And remember we're still 2.5 degrees away...
F: My God! [FO still struggles to spin the refused-to-be-spun trim wheel]
C: It's not possible, is it?
C: All right, we stop at that.

C: The reason that we have to try...
C: The reason we have to trim this manually is because the normal trim system wouldn't do this, OK.
C: It would require manual trim to get it away from this.
C: That's fine.
C: Trim it backward. [This time to illustrate the effort to trim the nose back up after "MCAS" brought the AC further nose down]
C: Trim it backward as you can.
F: Oh my God! I couldn't... [FO can't spin the wheel to trim up]
C: OK.
C: Eh...
C: Juan, press the red button! [CAPT called the sim operator...]
C: Press the red button now. [to stop the sim session]
C: This is at 340 knots.
C: And the trim is at...It's still at almost 2.5 degrees.
F: Yeah, 2.5 degrees.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 12:09 am

dragon6172 wrote:
PixelFlight wrote:
My conclusion is that the MCAS send command by a completely different circuit not show in that schematic.

MCAS comes from the FCC. Two things move the stab trim electrically, the column switches and the FCC. The FCC includes autopilot, STS, and MCAS

This is what I was thinking early, but the FCC signals are cut by the F/O COL CUTOUT SW MOD and the FDR data show the column was handled with force. So the FCC signals was cut for sure but there is still the MCAS activation signal acting on the stab trim motor. The same observation is from JT610 and ET302. The FCC signals includes autopilot and STS, but not MCAS I agree this is strange as the MCAS is believed to be a code added next to the STS code in the FCC, but if I am wrong, I have to read a plausible explanation why the COL AFT switch of the F/O COL CUTOUT SW MOD don't cut the FCC NOSE DOWN signal when the FDR record an aft force on the C/O column.

An other hint of a MCAS other circuit is that the MCAS ENGAGE signal energize a relay that cut the NOSE DOWN signal from the FCC. So the FCC NOSE DOWN can't be the signal from MCAS: he is cut two times in his path: at COL AFT and by MCAS ENGAGE relay.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 12:23 am

patplan wrote:
flybucky wrote:
PW100 wrote:
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

Thanks for that link regarding Mentour Pilot's decision to pull his video. But I did not have time to watch the 50 minute (!) video. Does someone have a summary? I only watched the first few minutes, where he said he pulled the video purely on his own decision, not due to any pressure from his company, Boeing, etc.


I watched the original sim session that was being pulled and also was smart enough to save the video as well...

The original sim session transcript [C=CAPT; F=FO]:
C: We have an IAS disagree.
C: So, IAS disagree memory items.
F: Autopilot if engaged, disengage.
C: Disengaged!
F: Autothrottle if engaged, disengage.
C: Disengaged!
F: Flight directors - Both up
F: With flaps up established a flight path 4 degrees and 75% N1.
C: So, 75% N1.
F: We have 77, 76,...
C: A little bit less...
F: And, there you go.
C: 4 degrees.
F: 4 degrees.

C: So I am trying to establish this now.
F: Check!
F: We are descending...?
F: We probably... Are you feeling troubled with...
F :Any trouble with the flight control?
C: Yeah, I'm trying to trim it but...
C: It continues to trim against me when I'm trimming
C: So state the malfunction, please.
F: Yeah, this doesn't look right. Looks like uh...
F: How do you feel the stabilizer, the trim system?
F: Can you control it?
C: I'm trimming it. It is responding but...
F: It's a runaway stabilizer, if you agree?
C: For every time that I trim backward, it keeps trimming forward.
F: It's trimming forward. Yeah, it's runaway stabilizer.
C: So, runaway stabilizer memory items...
C: And i'm trying to keep this thing at 4 degrees.
F: Control column, hold firmly.
C: I am... [CAPT is holding the yoke firmly with both hands]
F: Autopilot - if engaged, disengage.
C: It's disengaged.
F: Autothrottle - if engaged, disengage.
C: It's..., if you can disengage it for me, make sure that it's disengaged.
F: It's disengaged.
F: And, do you feel that the failure stop?
F: Negative?
C: No, it's still moving.
F: Stab trim cutoff switches to cutoff.
F: OK. It stops. It looks like it stops.
C: You can see now I'm using almost full back pressure here.
F: Exactly.
C: How many degrees nose down?
F: We have 4 units nose down now
C: 4 units nose down?
F: Yup.
C: OK, I'm struggling.
C: I'm actually using almost my full force to keep the aircraft level here.
F: Do you want me to help you?
C: What I would like to do.
C: Just for the sake of exercise, can you trim this forward? [to simulate MCAS trim AND]
C: See if we can reach even zero nose down.
C: And see if I can even hold it.

[FO is trying to crank the trim wheel to reach zero nose down, simulating MCAS AND]

C: So, now we are doing this just as an exercise!
C: Do not try this at home.
C: This...
C: We are at 300 knots now.
F: I'm fighting.
C: I'm sttrugling to to keep this aircraft flying.
F: My god! [FO surprised at how hard it is to trim further nose down]
C: Yeah, the thing is with higher speed the force on the stabilizer will be higher and higher as well.
C: So it becomes almost impossible to move it.
C: So we are now at about 3 degrees.
F: Yup. [FO still tries to continue trimming nose down, the wheels is so difficult to spin]
C: We're still about 3 degrees away from full nose down trim.
C: And I am using everything that I have. [CAPT still holding on to his yoke with both hands]
F: My God ! [the trim wheel barely move for the down trim]
C: This is realistic guys.
C: This is how much of effort it would take to trim the stabilizer at this kind of speed.
C: Umph... [Capt is still trying to hold on to his yoke with his hands]
C: I'm just in control of it, though. But it's getting harder and harder.
C: And remember we're still 2.5 degrees away...
F: My God! [FO still struggles to spin the refused-to-be-spun trim wheel]
C: It's not possible, is it?
C: All right, we stop at that.

C: The reason that we have to try...
C: The reason we have to trim this manually is because the normal trim system wouldn't do this, OK.
C: It would require manual trim to get it away from this.
C: That's fine.
C: Trim it backward. [This time to illustrate the effort to trim the nose back up after "MCAS" brought the AC further nose down]
C: Trim it backward as you can.
F: Oh my God! I couldn't... [FO can't spin the wheel to trim up]
C: OK.
C: Eh...
C: Juan, press the red button! [CAPT called the sim operator...]
C: Press the red button now. [to stop the sim session]
C: This is at 340 knots.
C: And the trim is at...It's still at almost 2.5 degrees.
F: Yeah, 2.5 degrees.

Many thanks for sharing this,
This fully confirm the "scary place" scenario and the impossibility to have an usable stab trim wheel.
This also confirm that the simulator correctly simulate the force on the stab trim wheel and that Boeing have not tested in a simulator the procedure published in the EAD.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 12:30 am

(If this has been addressed somewhere in the previous 93 parts of this thread let me know and I will go hunt for it.)

Regarding two of the criteria for MCAS to become active (the third is AoA input out of range): AP off and flaps up. I can understand AP off. The AP is not going to require the force gradient increase with air speed that a human might in order to to fly the airplane inside the envelope. Besides, one piece of software fighting another piece of software is pointless.

But why the requirement for flaps fully retracted? I'm assuming it's because with any amount of flaps deployed, the certification requirements regarding force gradient are always met. But if this isn't the case, is it because the MCAS engineers recognized that MCAS activating in any flaps-deployed situation (e.g., right after takeoff, approach and landing) would be dangerous due to likely near proximity to terrain?
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 1:06 am

hivue wrote:
(If this has been addressed somewhere in the previous 93 parts of this thread let me know and I will go hunt for it.)

Regarding two of the criteria for MCAS to become active (the third is AoA input out of range): AP off and flaps up. I can understand AP off. The AP is not going to require the force gradient increase with air speed that a human might in order to to fly the airplane inside the envelope. Besides, one piece of software fighting another piece of software is pointless.

But why the requirement for flaps fully retracted? I'm assuming it's because with any amount of flaps deployed, the certification requirements regarding force gradient are always met. But if this isn't the case, is it because the MCAS engineers recognized that MCAS activating in any flaps-deployed situation (e.g., right after takeoff, approach and landing) would be dangerous due to likely near proximity to terrain?

If I recall from earlier, flap extension changes the center of lift meaning the large nacelles have less effect on pitch up tendency.
Phrogs Phorever
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 1:11 am

PixelFlight wrote:
This is what I was thinking early, but the FCC signals are cut by the F/O COL CUTOUT SW MOD and the FDR data show the column was handled with force. So the FCC signals was cut for sure but there is still the MCAS activation signal acting on the stab trim motor. The same observation is from JT610 and ET302. The FCC signals includes autopilot and STS, but not MCAS I agree this is strange as the MCAS is believed to be a code added next to the STS code in the FCC, but if I am wrong, I have to read a plausible explanation why the COL AFT switch of the F/O COL CUTOUT SW MOD don't cut the FCC NOSE DOWN signal when the FDR record an aft force on the C/O column.

An other hint of a MCAS other circuit is that the MCAS ENGAGE signal energize a relay that cut the NOSE DOWN signal from the FCC. So the FCC NOSE DOWN can't be the signal from MCAS: he is cut two times in his path: at COL AFT and by MCAS ENGAGE relay.

Look at the upper cutout switch, bottom leg has FCC on one side and "A" on the other. "A" is direct input to the trim motor. I would guess this is the MCAS circuit. FCC-cutout switch-trim motor.
Phrogs Phorever
 
mwmav8r01
Posts: 68
Joined: Tue Dec 05, 2017 4:22 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 3:21 am

rheinwaldner wrote:
mwmav8r01 wrote:
In my opinion... I think thats what happened. The Captain asked the FO if it was working and he tried his yoke switch. But there is absolutely no way to know.

Why? Check the FDR plot.
Hint: there is no electric trim input visible so we absolutely know that he did not continue using the yoke switch.

[/list]

Noted. If my life depended on it I would try to get the other guy to try too. I have used the trim wheel in the MAX at a decent speed and had no issue. This part is a red flag to me. But I want to see the full report.
 
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gatibosgru
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 5:11 am

patplan wrote:
flybucky wrote:
PW100 wrote:
Here he explains why it was removed, but confirms his findings:
https://www.youtube.com/watch?v=q17vykscK0w

Thanks for that link regarding Mentour Pilot's decision to pull his video. But I did not have time to watch the 50 minute (!) video. Does someone have a summary? I only watched the first few minutes, where he said he pulled the video purely on his own decision, not due to any pressure from his company, Boeing, etc.


I watched the original sim session that was being pulled and also was smart enough to save the video as well...

The original sim session transcript [C=CAPT; F=FO]:
C: We have an IAS disagree.
C: So, IAS disagree memory items.
F: Autopilot if engaged, disengage.
C: Disengaged!
F: Autothrottle if engaged, disengage.
C: Disengaged!
F: Flight directors - Both up
F: With flaps up established a flight path 4 degrees and 75% N1.
C: So, 75% N1.
F: We have 77, 76,...
C: A little bit less...
F: And, there you go.
C: 4 degrees.
F: 4 degrees.

C: So I am trying to establish this now.
F: Check!
F: We are descending...?
F: We probably... Are you feeling troubled with...
F :Any trouble with the flight control?
C: Yeah, I'm trying to trim it but...
C: It continues to trim against me when I'm trimming
C: So state the malfunction, please.
F: Yeah, this doesn't look right. Looks like uh...
F: How do you feel the stabilizer, the trim system?
F: Can you control it?
C: I'm trimming it. It is responding but...
F: It's a runaway stabilizer, if you agree?
C: For every time that I trim backward, it keeps trimming forward.
F: It's trimming forward. Yeah, it's runaway stabilizer.
C: So, runaway stabilizer memory items...
C: And i'm trying to keep this thing at 4 degrees.
F: Control column, hold firmly.
C: I am... [CAPT is holding the yoke firmly with both hands]
F: Autopilot - if engaged, disengage.
C: It's disengaged.
F: Autothrottle - if engaged, disengage.
C: It's..., if you can disengage it for me, make sure that it's disengaged.
F: It's disengaged.
F: And, do you feel that the failure stop?
F: Negative?
C: No, it's still moving.
F: Stab trim cutoff switches to cutoff.
F: OK. It stops. It looks like it stops.
C: You can see now I'm using almost full back pressure here.
F: Exactly.
C: How many degrees nose down?
F: We have 4 units nose down now
C: 4 units nose down?
F: Yup.
C: OK, I'm struggling.
C: I'm actually using almost my full force to keep the aircraft level here.
F: Do you want me to help you?
C: What I would like to do.
C: Just for the sake of exercise, can you trim this forward? [to simulate MCAS trim AND]
C: See if we can reach even zero nose down.
C: And see if I can even hold it.

[FO is trying to crank the trim wheel to reach zero nose down, simulating MCAS AND]

C: So, now we are doing this just as an exercise!
C: Do not try this at home.
C: This...
C: We are at 300 knots now.
F: I'm fighting.
C: I'm sttrugling to to keep this aircraft flying.
F: My god! [FO surprised at how hard it is to trim further nose down]
C: Yeah, the thing is with higher speed the force on the stabilizer will be higher and higher as well.
C: So it becomes almost impossible to move it.
C: So we are now at about 3 degrees.
F: Yup. [FO still tries to continue trimming nose down, the wheels is so difficult to spin]
C: We're still about 3 degrees away from full nose down trim.
C: And I am using everything that I have. [CAPT still holding on to his yoke with both hands]
F: My God ! [the trim wheel barely move for the down trim]
C: This is realistic guys.
C: This is how much of effort it would take to trim the stabilizer at this kind of speed.
C: Umph... [Capt is still trying to hold on to his yoke with his hands]
C: I'm just in control of it, though. But it's getting harder and harder.
C: And remember we're still 2.5 degrees away...
F: My God! [FO still struggles to spin the refused-to-be-spun trim wheel]
C: It's not possible, is it?
C: All right, we stop at that.

C: The reason that we have to try...
C: The reason we have to trim this manually is because the normal trim system wouldn't do this, OK.
C: It would require manual trim to get it away from this.
C: That's fine.
C: Trim it backward. [This time to illustrate the effort to trim the nose back up after "MCAS" brought the AC further nose down]
C: Trim it backward as you can.
F: Oh my God! I couldn't... [FO can't spin the wheel to trim up]
C: OK.
C: Eh...
C: Juan, press the red button! [CAPT called the sim operator...]
C: Press the red button now. [to stop the sim session]
C: This is at 340 knots.
C: And the trim is at...It's still at almost 2.5 degrees.
F: Yeah, 2.5 degrees.


Thanks for sharing this. What a terrifying experience it must have been irl.
@DadCelo
 
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PixelFlight
Posts: 650
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 5:39 am

dragon6172 wrote:
PixelFlight wrote:
This is what I was thinking early, but the FCC signals are cut by the F/O COL CUTOUT SW MOD and the FDR data show the column was handled with force. So the FCC signals was cut for sure but there is still the MCAS activation signal acting on the stab trim motor. The same observation is from JT610 and ET302. The FCC signals includes autopilot and STS, but not MCAS I agree this is strange as the MCAS is believed to be a code added next to the STS code in the FCC, but if I am wrong, I have to read a plausible explanation why the COL AFT switch of the F/O COL CUTOUT SW MOD don't cut the FCC NOSE DOWN signal when the FDR record an aft force on the C/O column.

An other hint of a MCAS other circuit is that the MCAS ENGAGE signal energize a relay that cut the NOSE DOWN signal from the FCC. So the FCC NOSE DOWN can't be the signal from MCAS: he is cut two times in his path: at COL AFT and by MCAS ENGAGE relay.

Look at the upper cutout switch, bottom leg has FCC on one side and "A" on the other. "A" is direct input to the trim motor. I would guess this is the MCAS circuit. FCC-cutout switch-trim motor.

Very possible.
 
Spotter1967
Posts: 11
Joined: Fri May 14, 2010 12:13 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 08, 2019 6:40 am

Boeing made many mistakes in designing and implementing MCAS. This post provides an overview of those mistakes.
https://feitoffake.wordpress.com/2019/0 ... g-737-max/

The major mistakes
1. Use only one AOA-sensor for input to MCAS
2. No checks by MCAS software of data input from AOA-sensor makes sense. A AOA-angle of 74,4 does not make sense at all
3. No information in the FCOM about MCAS
4. MCAS can make huge Aircraft Nose Down commands, which is hard to compensate by the crew using trim switches
5. Disable the ability to cutoff the 'autopilot command' to the stabilzer using the cutout switches. This was available in the NG-series

These simple steps would have prevented two fatal crashes.

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