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.

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?

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.

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.

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.

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.

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?

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.

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.

SheikhDjibouti wrote:

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

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.

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.

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.

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.

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.

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.

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.

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:

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.

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

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

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.

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.

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...

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.

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.

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.

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.

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.

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.

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.

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".

PW100 wrote:

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

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.

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.

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.

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.

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.

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)?

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)?

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

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.

PixelFlight wrote:

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

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.

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.

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

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.

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?

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.

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.

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.

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.