SteinarN
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 8:00 pm

dragon6172 wrote:
I believe it is the AoA indicator that is an option. If you don't have an AoA indicator, you don't need an AoA disagree caution.


Well, in this case it seems that an AoA disagree message would have been very helpful for the maintenance guys when they was trying to diagnose the airplane after the previous flights.
It could even be conceivable that such a message might have been helpful for the pilots when they were in manual flight mode and the automatic trim went awry.
 
dakota123
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 8:02 pm

BlueSky1976 wrote:
Tucker1 wrote:
Knee-jerk action. If my next 10+ flights were on a max 8, I wouldn't think twice about getting on board. There should be more investigation into pilot response before the FAA comes a conclusion like this so soon. Now if my next 10+ flights on the max 8 were with lion air, I WOULD think twice about getting aboard. even the FIRST flight...


I suggest you do some reading on faulty dampers Boeing kept installing in 737s since the beginning of its production until USAir Pittsburgh crash.
Boeing has history of faulty designs and LionAir crash could be a result of one, as well - you know?


OK, I'll bite.

Was going to give you the benefit of the doubt that maybe your choice of words was just off a bit, but then read your tag line. Really? Then you won't be flying Airbus any time soon either, I guess? News for you, there isn't a perfect airliner design flying.

Anyway, I had studied the 737 PCU (not damper.) issue extensively at one point (along with other hard-to-figure-out engineering/design failures). There was an excellent, really in depth almost-book about it on-line, but I can't find it any longer. This article isn't bad, although it omits some of the early root-cause efforts: https://www.airspacemag.com/flight-toda ... 23/?page=1 Provides a decent discussion of why it took so long to find the issue.
 
edmountain
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 8:49 pm

Revelation wrote:
edmountain wrote:
The following hypothetical system designs would also be subject to similar procedural failures. As a result they can be remedied without any major changes to the equipment.

A vehicle's cruise control no longer receives valid speed information. The system responds by opening the throttle wide open because, hey, every driver should know how to use the break.

A different vehicle's traction control system no longer receives valid speed information from one of the wheels. The system responds by locking the wheel in question because, hey, every driver should know how to recover from a spin.

An elevator door can no longer tell if someone is in the entrance to the lift or not. The system responds by slamming the door shut because, hey, every little old lady should be able to prop open a 50kg door.

An insulin pump no longer receives valid information about blood sugar. The system responds by injecting a bolus of insulin because, hey, every diabetic should know how to respond to a hypoglycemic seizure.

Basically you're comparing systems with no operators (automatic insulin delivery) or untrained operators (elevators) or minimally trained operators (automobiles) to ones operated by professionals with recurring training. IMHO you are doing so in a very exaggerated way, and given what we know so far, an unjustified way.

It's clear you have no experience with insulin pumps if you think they function without an operator--but that's besides the point.

Yes, I exaggerated. I did so to illustrate the apparent irrationality to an outside observer of a situation wherein data that are known to be erroneous form the basis of command inputs into a system. Seeing as how the FAA issued an emergency AD describing an "unsafe condition" that "is likely to exist or develop in other products of the same type" the exaggeration for illustrative purposes seems completely justified.

Consider the unsafe condition. As per the AD, this condition allows "erroneously high single angle of attack sensor input" to cause "repeated nose-down trim commands" that could cause the "flight crew to have difficulty controlling the airplane" to the point of "possible impact with terrain." Is there a good reason for the flight control system of the 737MAX to respond to erroneous data rather than rejecting it? Perhaps--but I've yet to see one provided here. Is it a good enough safety check to rely on "professionals with recurring training" to detect and rectify the unsafe condition? The answer to that lies at the bottom of the Java Sea but the fact that the FAA considers the remedy in the AD as interim would indicate otherwise.
 
osiris30
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 8:52 pm

PW100 wrote:
osiris30 wrote:
This is pilot error but IMHO the Lion Air crash was the fault of the previous pilots who did not report AOA issues in the maintenance book. We saw the log book and there was no reference to any AOA issues. Just airspeed and trim. Had they reported the AOA mismatch this would have never happened.

How do you know they could/should have recognized AoA issue? Could its symptoms perhaps have somehow been "camouflaged" by the unreliable air speed issues? How well was the AoA apparent to the pilots.
I'll accept that one crew may have missed it, but if three or four crews missed it, that there seems to be more to it. Mind you, that may very well be a company procedure/training/culture thing (or lack off rather). But it may also be that such information was not recognizable for the pilots and only the 1700 channel DFDR was able to detect such.



Depending on the configuration it would have presented AOA disagree to the crew directly (I understand that for some reason AOA disagree is an optional warning light.. Which boggles the hell out of my mind). Also if Lion has deployed the maintenance software from Boeing I *believe* it would have reported the AOA problem as well. We do know that the AOA sensors were changed prior to the flight BEFORE the flight that crashed, so it possible they had been reported back then, so we don't know if 3 or 4 crews missed it. Only that 1 did for sure. I haven't seen a picture of the logbook for any prior flights to know. Earlier crews may have reported AOA issues.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
osiris30
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 8:55 pm

dragon6172 wrote:

osiris30 wrote:

This is why I have added did AOA disagree report in a later reply. This is a fair point. AOA disagree is optional apparently?? I do not know why any airline would ever opt out for that but... There are a few questions to be answered but my assumption is aoa disagree would have reported If not it moves this to airline mgmt who didnt select it and maintenance who didn't do a thorough job.

I believe it is the AoA indicator that is an option. If you don't have an AoA indicator, you don't need an AoA disagree caution.


That only makes slightly more sense, as AOA Disagree is (in my opinion) potentially dangerous enough and important enough to at least report to the flight crew, regardless of if you have the AOA indicator or not.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
KCaviator
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 9:16 pm

This accident and subsequent loss of life resulted from Boeing-error, not pilot-error.

Too bad this will never be the official result because of politics and money.
Last edited by KCaviator on Thu Nov 08, 2018 9:27 pm, edited 2 times in total.
 
ikramerica
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 9:17 pm

edmountain wrote:
osiris30 wrote:
...

This accident should have been prevented and without any major changes to pilot flying techniques or aircraft. This is a procedural failure at its root. Equipment breaks all the time. A faulty pitot or aoa should jot be the root cause ever to an aircraft crashing.

The following hypothetical system designs would also be subject to similar procedural failures. As a result they can be remedied without any major changes to the equipment.

A vehicle's cruise control no longer receives valid speed information. The system responds by opening the throttle wide open because, hey, every driver should know how to use the break.

A different vehicle's traction control system no longer receives valid speed information from one of the wheels. The system responds by locking the wheel in question because, hey, every driver should know how to recover from a spin.

An elevator door can no longer tell if someone is in the entrance to the lift or not. The system responds by slamming the door shut because, hey, every little old lady should be able to prop open a 50kg door.

An insulin pump no longer receives valid information about blood sugar. The system responds by injecting a bolus of insulin because, hey, every diabetic should know how to respond to a hypoglycemic seizure.

1. Yes every driver knows that the stop cruise control you brake. It will immediately stop auto speed.
2. The default is disengage and light a warning.
3. The default is to open, not close. Then to go union.
4. These are as tested as an aircraft and the scenario is ludicrous. It would beep and show and error that you couldnt ignore.

All your scenarios are ludicrous.
Of all the things to worry about... the Wookie has no pants.
 
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SEPilot
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 9:55 pm

So why does the MAX have less inherent stability than the NGs? My understanding is that that would be from the CG envelope being moved further aft. But I thought that the fuselage and wing changes were minimal, and the engines are heavier, which would move the CG forward, not aft. Is the horizontal stabilizer smaller? But I don’t think that would reduce inherent stability, it would just reduce control authority.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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PW100
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:04 pm

osiris30 wrote:
We do know that the AOA sensors were changed prior to the flight BEFORE the flight that crashed, so it possible they had been reported back then, so we don't know if 3 or 4 crews missed it. Only that 1 did for sure. I haven't seen a picture of the logbook for any prior flights to know. Earlier crews may have reported AOA issues.


Yet you had no issues writing this:

osiris30 wrote:
This is pilot error but IMHO the Lion Air crash was the fault of the previous pilots who did not report AOA issues in the maintenance book. We saw the log book and there was no reference to any AOA issues. Just airspeed and trim. Had they reported the AOA mismatch this would have never happened.


We don't even know what AoA indicator option package Lion Air has in their fleet. We don't know how visible the AoA issue was in the cockpit. We only know at this stage it is visible and detectable on the 1700 channel DFDR.
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
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PW100
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:06 pm

SEPilot wrote:
So why does the MAX have less inherent stability than the NGs? My understanding is that that would be from the CG envelope being moved further aft. But I thought that the fuselage and wing changes were minimal, and the engines are heavier, which would move the CG forward, not aft. Is the horizontal stabilizer smaller? But I don’t think that would reduce inherent stability, it would just reduce control authority.

Perhaps the CoG was moved a little forward to improve drag efficiency (reduced tail loading).
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
ikramerica
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:14 pm

ikramerica wrote:
edmountain wrote:
osiris30 wrote:
...

This accident should have been prevented and without any major changes to pilot flying techniques or aircraft. This is a procedural failure at its root. Equipment breaks all the time. A faulty pitot or aoa should jot be the root cause ever to an aircraft crashing.

The following hypothetical system designs would also be subject to similar procedural failures. As a result they can be remedied without any major changes to the equipment.

A vehicle's cruise control no longer receives valid speed information. The system responds by opening the throttle wide open because, hey, every driver should know how to use the break.

A different vehicle's traction control system no longer receives valid speed information from one of the wheels. The system responds by locking the wheel in question because, hey, every driver should know how to recover from a spin.

An elevator door can no longer tell if someone is in the entrance to the lift or not. The system responds by slamming the door shut because, hey, every little old lady should be able to prop open a 50kg door.

An insulin pump no longer receives valid information about blood sugar. The system responds by injecting a bolus of insulin because, hey, every diabetic should know how to respond to a hypoglycemic seizure.

1. Yes every driver knows that the stop cruise control you brake. It will immediately stop auto speed.
2. The default is disengage and light a warning.
3. The default is to open, not close. Then to go union.
4. These are as tested as an aircraft and the scenario is ludicrous. It would beep and show and error that you couldnt ignore.

All your scenarios are ludicrous.

As for why the aircraft would pitch down, it’s because it’s preventjng a stall. Instinct should be to pull up to level to compensate and then disengage system.

Look at the AF accident. They pulled up into a stall.
Of all the things to worry about... the Wookie has no pants.
 
dakota123
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:15 pm

According to http://www.b737.org.uk/737maxdiffs.htm#diffs the thrust line is different. Could have something to do with it: "The thrust line has changed from the NG because the engines had to be moved forward and up to accomodate (sic) the larger fan diameter. Any handling differences as a result of this have been tuned out by Boeing in the flight control system to make the types feel the same to crew. This was necessary for certification under the same type certificate."

(Mildly) interestingly, there is a photo of the speed trim fail caution light towards the bottom of the page.
 
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SEPilot
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:39 pm

PW100 wrote:
SEPilot wrote:
So why does the MAX have less inherent stability than the NGs? My understanding is that that would be from the CG envelope being moved further aft. But I thought that the fuselage and wing changes were minimal, and the engines are heavier, which would move the CG forward, not aft. Is the horizontal stabilizer smaller? But I don’t think that would reduce inherent stability, it would just reduce control authority.

Perhaps the CoG was moved a little forward to improve drag efficiency (reduced tail loading).

Moving the CG forward would enhance stability, not decrease it. But without other changes the CG would have moved forward as the engines are heavier AND farther forward. To move the CG aft you need to shift weight to the tail. Without adding dead weight the only real way to do that is move the wing back on the fuselage. It would’t take much; was that done? I don’t think changing the thrust line would affect stability; it would affect trim and possibly control authority.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
CO953
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 10:53 pm

Speaking from an auto-mechanic's perspective, instead of a pilot's, the warning about the trim system reminds me of when anti-lock braking systems began to become more popular in cars.
Drivers were cautioned that their old style of emergency braking would not work properly if used in an ABS-equipped vehicle, and could actually impair/increase stopping distance.

Traditional braking systems required drivers to pump (quickly apply and release) the brakes, so as to prevent a skid in the event of a panic stop.

ABS systems performed that pulsating brake-caliper action on BEHALF of the driver, and so drivers were told to just go ahead and mash the brake pedal, and let the system do the modulation for them.
The act of applying the pump-and-release old-style driver foot action actually interfered with/confused the ABS systems, with the result that the driver/ABS interface resulted in a worse outcome, than with the combination of a skilled driver and a traditional braking system.

I remember very clearly the first time I had to make a panic stop in an ABS-equipped rental car. Even though my MIND knew that I was supposed to just apply steady, hard force, and let the ABS system do the pulsation, my FOOT followed my old reflexes and pumped the brake pedal - resulting in my almost rear-ending another car.

Let me just provide the previous as an overall thinking point, however/if it may apply in some way.
 
dragon6172
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 11:06 pm

SteinarN wrote:
dragon6172 wrote:
I believe it is the AoA indicator that is an option. If you don't have an AoA indicator, you don't need an AoA disagree caution.


Well, in this case it seems that an AoA disagree message would have been very helpful for the maintenance guys when they was trying to diagnose the airplane after the previous flights.
It could even be conceivable that such a message might have been helpful for the pilots when they were in manual flight mode and the automatic trim went awry.

I would guess that the aircraft has some sort of "maintenance mode" that stores errors and other info that the maintainers can access.
Phrogs Phorever
 
edmountain
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 11:16 pm

ikramerica wrote:
ikramerica wrote:
edmountain wrote:
The following hypothetical system designs would also be subject to similar procedural failures. As a result they can be remedied without any major changes to the equipment.

A vehicle's cruise control no longer receives valid speed information. The system responds by opening the throttle wide open because, hey, every driver should know how to use the break.

A different vehicle's traction control system no longer receives valid speed information from one of the wheels. The system responds by locking the wheel in question because, hey, every driver should know how to recover from a spin.

An elevator door can no longer tell if someone is in the entrance to the lift or not. The system responds by slamming the door shut because, hey, every little old lady should be able to prop open a 50kg door.

An insulin pump no longer receives valid information about blood sugar. The system responds by injecting a bolus of insulin because, hey, every diabetic should know how to respond to a hypoglycemic seizure.

1. Yes every driver knows that the stop cruise control you brake. It will immediately stop auto speed.
2. The default is disengage and light a warning.
3. The default is to open, not close. Then to go union.
4. These are as tested as an aircraft and the scenario is ludicrous. It would beep and show and error that you couldnt ignore.

All your scenarios are ludicrous.

As for why the aircraft would pitch down, it’s because it’s preventjng a stall. Instinct should be to pull up to level to compensate and then disengage system.

Look at the AF accident. They pulled up into a stall.

The issue is not how the system behaves when receiving valid inputs, it's how the system behaves when the inputs are known to be erroneous.

Once again, from the AD:

analysis performed by the manufacturer showing that if an erroneously high single angle of attack (AOA) sensor input is received by the flight control system, there is a potential for repeated nose-down trim commands


This is analogous to an insulin pump injecting a bolus of insulin when it knows the blood sugar readings are erroneous. Perhaps there's a good reason the system was designed this way but nobody around here has provided one.
 
dtw2hyd
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 11:20 pm

Question abt runaway trim.

Does it go on for just 10 seconds, or forever in 10-second increments.

How many seconds crew has to stop and regain control from say 5000 ft. altitude?
 
dakota123
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 11:25 pm

Have a look at figure 1: https://www.boeing.com/commercial/aerom ... 01txt.html

Moving CG forward requires (of course) more stick force and therefore requires more trim authority. Which would fit with the heavier engine, farther forward idea.

That thing about MAX longitudinal stability being different than the NG was from a friend of a poster on here, not a Boeing communique AFAIK? So maybe not entirely accurate?

Thrust line does affect stability, but it's the opposite, above (or closer to) cg increases stability.
 
benjjk
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Re: FAA issues emergency 737 Max airworthiness order

Thu Nov 08, 2018 11:45 pm

dakota123 wrote:
Have a look at figure 1: https://www.boeing.com/commercial/aerom ... 01txt.html

Moving CG forward requires (of course) more stick force and therefore requires more trim authority. Which would fit with the heavier engine, farther forward idea.

That thing about MAX longitudinal stability being different than the NG was from a friend of a poster on here, not a Boeing communique AFAIK? So maybe not entirely accurate?

Thrust line does affect stability, but it's the opposite, above (or closer to) cg increases stability.


This does make sense. I posted a message written by a chief pilot for a non-Max operator, which only said the longitudinal stability was different to the NG, not more or less. Maybe the poster erroneously assumed that meant decreased stability?
 
Elshad
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 12:05 am

Aptivaboy wrote:
Question: does the MAX instrument display contain a backup old fashioned (non-digital) steam guage artificial horizon? And, if so, is it linked to a different AOA system?

Thanks for any input. Non-pilot here trying to understand a few things.


There is no "steam guage" ADI but there is a backup Integrated Standby Flight Display (ISFD) in the middle between the LCD displays. I don't think it's specific to the MAX though, as later NGs also got rid of the separate back up steam gauges (you can see the blanking panels where they used to be).

Not sure if they use a separate AOA system though.
 
osiris30
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 12:12 am

PW100 wrote:
osiris30 wrote:
We do know that the AOA sensors were changed prior to the flight BEFORE the flight that crashed, so it possible they had been reported back then, so we don't know if 3 or 4 crews missed it. Only that 1 did for sure. I haven't seen a picture of the logbook for any prior flights to know. Earlier crews may have reported AOA issues.


Yet you had no issues writing this:

osiris30 wrote:
This is pilot error but IMHO the Lion Air crash was the fault of the previous pilots who did not report AOA issues in the maintenance book. We saw the log book and there was no reference to any AOA issues. Just airspeed and trim. Had they reported the AOA mismatch this would have never happened.


We don't even know what AoA indicator option package Lion Air has in their fleet. We don't know how visible the AoA issue was in the cockpit. We only know at this stage it is visible and detectable on the 1700 channel DFDR.


If you read further down I clarified my statement as I had forgotten AOA warning is not guaranteed to exist. I am unsure if Lion's planes have it. And said as much.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
maint123
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 1:13 am

dtw2hyd wrote:
Question abt runaway trim.

Does it go on for just 10 seconds, or forever in 10-second increments.

How many seconds crew has to stop and regain control from say 5000 ft. altitude?

This question will be studiously ignored or deleted by the experts here , as mine was.
I had asked precisely this question couple of days back - twice, as even to a layman a height of 5000 ft at a speed of 800 ft per sec is covered in 6 seconds.
 
osiris30
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 2:26 am

maint123 wrote:
dtw2hyd wrote:
Question abt runaway trim.

Does it go on for just 10 seconds, or forever in 10-second increments.

How many seconds crew has to stop and regain control from say 5000 ft. altitude?

This question will be studiously ignored or deleted by the experts here , as mine was.
I had asked precisely this question couple of days back - twice, as even to a layman a height of 5000 ft at a speed of 800 ft per sec is covered in 6 seconds.


It trims down slowly over a period of 10 seconds and then pauses and if AOA is still out of whack it will trim again. That is my reading of the manual on it.

It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
buzzard302
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 2:50 am

osiris30 wrote:
maint123 wrote:
dtw2hyd wrote:
Question abt runaway trim.

Does it go on for just 10 seconds, or forever in 10-second increments.

How many seconds crew has to stop and regain control from say 5000 ft. altitude?

This question will be studiously ignored or deleted by the experts here , as mine was.
I had asked precisely this question couple of days back - twice, as even to a layman a height of 5000 ft at a speed of 800 ft per sec is covered in 6 seconds.


It trims down slowly over a period of 10 seconds and then pauses and if AOA is still out of whack it will trim again. That is my reading of the manual on it.

It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.


Which means these pilots could have been distracted and preoccupied and didn't realize the plane was about to go into a dive. Eastern Airlines 401 flew into the ground because pilots were paying attention to an indicator light and didn't realize autopilot was disconnected. We need CVR for this accident to help understand what these pilots were facing.
 
osiris30
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 3:31 am

buzzard302 wrote:
osiris30 wrote:
maint123 wrote:
This question will be studiously ignored or deleted by the experts here , as mine was.
I had asked precisely this question couple of days back - twice, as even to a layman a height of 5000 ft at a speed of 800 ft per sec is covered in 6 seconds.


It trims down slowly over a period of 10 seconds and then pauses and if AOA is still out of whack it will trim again. That is my reading of the manual on it.

It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.


Which means these pilots could have been distracted and preoccupied and didn't realize the plane was about to go into a dive. Eastern Airlines 401 flew into the ground because pilots were paying attention to an indicator light and didn't realize autopilot was disconnected. We need CVR for this accident to help understand what these pilots were facing.


I should mention based on my understanding of the system that it would have in fact been closer to a minute+a few seconds based on the fact it wouldn't have reached maximum swing until ~30 seconds from start. Doesn't invalidate your point at all, just reran the numbers in my head.

I should also mention the flight data does not match the decent profile that trim alone would have caused.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
maint123
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 4:42 am

The FAA directive -

"(h) AFM Revision: Operating Procedures
Within 3 days after receipt of this AD, revise the Operating Procedures chapter of the
applicable AFM to include the information in figure 2 to paragraph (h) of this AD.
Figure 2 to paragraph (h) of this AD – Operating Procedures
Required by AD 2018-23-51
Runaway Stabilizer
Disengage autopilot and control airplane pitch attitude with control column
and main electric trim as required. If relaxing the column causes the trim to
move, set stabilizer trim switches to CUTOUT. If runaway continues, hold
the stabilizer trim wheel against rotation and trim the airplane manually.
Note: The 737-8/-9 uses a Flight Control Computer command of pitch
trim to improve longitudinal handling characteristics. In the event of
erroneous Angle of Attack (AOA) input, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds.
In the event an uncommanded nose down stabilizer trim is experienced
on the 737-8/-9, in conjunction with one or more of the indications or
effects listed below, do the existing AFM Runaway Stabilizer
procedure above, ensuring that the STAB TRIM CUTOUT switches
are set to CUTOUT and stay in the CUTOUT position for the
remainder of the flight.
An erroneous AOA input can cause some or all of the following
indications and effects:
• Continuous or intermittent stick shaker on the affected side only.
• Minimum speed bar (red and black) on the affected side only.
• Increasing nose down control forces.
• IAS DISAGREE alert.
• ALT DISAGREE alert.
• AOA DISAGREE alert (if the option is installed).
• FEEL DIFF PRESS light.
• Autopilot may disengage.
• Inability to engage autopilot.
Initially, higher control forces may be needed to overcome any
stabilizer nose down trim already applied. Electric stabilizer trim can be
used to neutralize control column pitch forces before moving the STAB
TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be
used before and after the STAB TRIM CUTOUT switches are moved
to CUTOUT."

I see the pilots having a very hard time with so many simultaneous alarms.
Best to ground all Max planes till a proper solution to this defective logic is given by Boeing.
Not good enough to just tell the pilots that your plane has a problem , deal with it.
 
T54A
Posts: 132
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Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 6:03 am

iamlucky13 wrote:
T54A wrote:
How does a new type get through a certification process without this been picked up? Is the regulator falling short of its responsibility?


That suggests it is not a common issue, perhaps related to fairly specific environmental conditions not identified as a risk factor, perhaps due to in-service damage not corrected for some reason, perhaps due to a manufacturing defect not present on any of the test aircraft, etc, etc.

The 200 aircraft in service represent 50 times as many aircraft as were flight tested, and accrue as many hours in a day or two as the entire Max 8 test program.

Just an anecdotal commentary as somebody with experience in test engineering - some problems are really difficult to replicate in even well-designed tests.


Considering the B748 horizontal stab flutter, the B788 elec problems, B787 RR engine problems, now Max issue, does it not suggest the current Boeing flight test profile is lacking. Is the commercial and accounting department not putting unreasonable pressure on the Flight Test Dept to rush aircraft into service?

Did we see similar problems with B744, B757, B767, B777, A320 (perhaps), A330, A340 and A380.
T6, Allouette 3, Oryx, King Air, B1900, B727, B744, A319, A342/3/6 A332/3
 
SteinarN
Posts: 110
Joined: Mon Dec 29, 2014 1:26 pm

Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 6:19 am

osiris30 wrote:
It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.


I will sugest that you make your self aware of the difference between AoA and pitch so you dont spread misinformation.
In steady flight one sensor can correctly read 2 degrees AoA and the other a erouneously 20 degrees.. The plane pitches down reaching a steady 20 degree pitch down attitude. The working sensor will still read about 2 degrees AoA and the faulty one will still read about 20 degrees AoA.
 
osiris30
Posts: 2373
Joined: Sat Sep 30, 2006 10:16 am

Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 8:39 am

SteinarN wrote:
osiris30 wrote:
It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.


I will sugest that you make your self aware of the difference between AoA and pitch so you dont spread misinformation.
In steady flight one sensor can correctly read 2 degrees AoA and the other a erouneously 20 degrees.. The plane pitches down reaching a steady 20 degree pitch down attitude. The working sensor will still read about 2 degrees AoA and the faulty one will still read about 20 degrees AoA.


Explain to me how the aoa wouldn't change exactly when constantly pitching down. Maybe I am missing something but if pitch is constantly being lowered aoa should continue to change as the relative motion should be changing constantly. There may be some equalibrium point but if the pitch down is constant shouldn't the aoa continue to change until to motion vector stabilizes? Maybe I am missing something it is late so happy to be corrected.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
SteinarN
Posts: 110
Joined: Mon Dec 29, 2014 1:26 pm

Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 9:14 am

osiris30 wrote:
SteinarN wrote:
osiris30 wrote:
It should also be noted we have a max deviance of 20 degrees on the AOA data from the FDR, which means the aircraft would pitch down a maximum of 18.5 degree roughly (assuming 1.5 degrees is normal AOA)

That means the rapid loss of altitude in the logs cannot be solely attributed to the auto trim and your 6-second number becomes something more on the order of 30 seconds, which IS more than enough to grab the yoke and do something.


I will sugest that you make your self aware of the difference between AoA and pitch so you dont spread misinformation.
In steady flight one sensor can correctly read 2 degrees AoA and the other a erouneously 20 degrees.. The plane pitches down reaching a steady 20 degree pitch down attitude. The working sensor will still read about 2 degrees AoA and the faulty one will still read about 20 degrees AoA.


Explain to me how the aoa wouldn't change exactly when constantly pitching down. Maybe I am missing something but if pitch is constantly being lowered aoa should continue to change as the relative motion should be changing constantly. There may be some equalibrium point but if the pitch down is constant shouldn't the aoa continue to change until to motion vector stabilizes? Maybe I am missing something it is late so happy to be corrected.


The AOA tells you something about how much lift the wing is generating. At zero degres AOA the wing is generating zero lift. At steady flight in normal speeds you might have 2 degrees AOA as you correctly suggest in another post. The wing is then generating the same lift as the weight of the aircraft and the aircraft flies happily away at constant altitude and 1 G.
Now, assume that one AOA sensor is way off and in this example is indicating an AOA which is 20 degrees to high, that is one sensor indicates the correct 2 degres and the other one an incorrect 22 degres.
Then we pitch down the aircraft to a 10 degrees pitch down attitude. We wait until the aircraft is stabilized at this attitude. The aircraft is now flying along a line pitching down 10 degrees and the aircrafts altitude is decreasing with a constant number of feet per minute. But the G experienced by the aircraft and its passengers and crew is still 1 G, since the aircraft is following a straight line with no vertical acceleration. Therefore the true AOA must still be the same ca 2 degrees as previously since the wings still need to generate the same lift as the weight of the aircraft, which has not changed. So, the correct working AOA sensor is still indicating ca 2 degrees AOA, the faulty sensor is still indicating 20 degrees to high AOA, that is it is still indicating ca 22 degrees AOA.

Lets say we pitch down the aircraft to an insane 90 degrees pitch down attitude and stabilize the aircraft. Now the wing dont need to generate any lift since we are flying straight down. The true AOA is therefore zero degrees.. The correct AOA sensor is indicating zero degree, the faulty one 20 degrees more, that is the faulty sensor will now indicate 20 degrees AOA.

So, we see that as the aircraft pitches down the true AOA gradually decreases to zero degrees as long as a particular attitude is stabilized. Any AOA sensor with a constant positive error will therefore never reach a value of zero degrees in any constant pitch attitude between level flight and 90 degrees straight down.

I can add that this explanation is valid as long as the roll rate is zero or at least very low.

Edit: I have omitted some details, like a possibly angular deviation between the wing chord line and and the fuselage senterline and some other minor details. So if someone was going to be very pedantic (s)he could find some minor errors in my explanation, but the principle still holds true.
 
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AirlineCritic
Posts: 1441
Joined: Sat Mar 14, 2009 1:07 pm

Re: FAA issues emergency 737 Max airworthiness order

Fri Nov 09, 2018 12:29 pm

Osiris30: What SteinarN said. You've been quick to come to conclusions about blame, and now are quick to come to conclusion about how steep descent the aircraft entered. Perhaps it would be useful to slow down a bit and think about the possibilities.

We don't have the full FDR data. We don't know what failure mode the sensor had, if it indeed was faulty, or if the computers were faulty instead. I could easily imagine a sensor-being-stuck situation where the AoA is according to the sensor always too high, and the plane perpetually attempts to lower the nose lower and lower. But it is not the only possible fault mode.
 
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NeBaNi
Posts: 346
Joined: Sun Dec 20, 2009 10:45 am

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 1:46 am

SteinarN wrote:
osiris30 wrote:
SteinarN wrote:

I will sugest that you make your self aware of the difference between AoA and pitch so you dont spread misinformation.
In steady flight one sensor can correctly read 2 degrees AoA and the other a erouneously 20 degrees.. The plane pitches down reaching a steady 20 degree pitch down attitude. The working sensor will still read about 2 degrees AoA and the faulty one will still read about 20 degrees AoA.


Explain to me how the aoa wouldn't change exactly when constantly pitching down. Maybe I am missing something but if pitch is constantly being lowered aoa should continue to change as the relative motion should be changing constantly. There may be some equalibrium point but if the pitch down is constant shouldn't the aoa continue to change until to motion vector stabilizes? Maybe I am missing something it is late so happy to be corrected.


The AOA tells you something about how much lift the wing is generating. At zero degres AOA the wing is generating zero lift.

When you have a non-symmetric (possibly supercritical) airfoil like in the case of the 737, it is not necessarily true that you have zero lift at zero degrees angle of attack. There can be positive lift at zero AoA.
 
SteinarN
Posts: 110
Joined: Mon Dec 29, 2014 1:26 pm

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 8:34 am

NeBaNi wrote:
SteinarN wrote:
The AOA tells you something about how much lift the wing is generating. At zero degres AOA the wing is generating zero lift.

When you have a non-symmetric (possibly supercritical) airfoil like in the case of the 737, it is not necessarily true that you have zero lift at zero degrees angle of attack. There can be positive lift at zero AoA.


Well, i said I had omitted some minor details, I think this is in the minor details category. The principle in my explanation still holds true.
But anyway, thanks for mentioning this fact.
 
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seahawk
Posts: 7446
Joined: Fri May 27, 2005 1:29 am

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 11:40 am

In combination with faulty airspeed sensors, it should make a not easy scenario to trouble shoot.
 
ubeema
Posts: 319
Joined: Thu Aug 23, 2012 3:48 am

FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 12:01 pm

SteinarN wrote:
The AOA tells you something about how much lift the wing is generating. At zero degres AOA the wing is generating zero lift. At steady flight in normal speeds you might have 2 degrees AOA as you correctly suggest in another post. The wing is then generating the same lift as the weight of the aircraft and the aircraft flies happily away at constant altitude and 1 G.
Now, assume that one AOA sensor is way off and in this example is indicating an AOA which is 20 degrees to high, that is one sensor indicates the correct 2 degres and the other one an incorrect 22 degres.
Then we pitch down the aircraft to a 10 degrees pitch down attitude. We wait until the aircraft is stabilized at this attitude. The aircraft is now flying along a line pitching down 10 degrees and the aircrafts altitude is decreasing with a constant number of feet per minute. But the G experienced by the aircraft and its passengers and crew is still 1 G, since the aircraft is following a straight line with no vertical acceleration. Therefore the true AOA must still be the same ca 2 degrees as previously since the wings still need to generate the same lift as the weight of the aircraft, which has not changed. So, the correct working AOA sensor is still indicating ca 2 degrees AOA, the faulty sensor is still indicating 20 degrees to high AOA, that is it is still indicating ca 22 degrees AOA.

Lets say we pitch down the aircraft to an insane 90 degrees pitch down attitude and stabilize the aircraft. Now the wing dont need to generate any lift since we are flying straight down. The true AOA is therefore zero degrees.. The correct AOA sensor is indicating zero degree, the faulty one 20 degrees more, that is the faulty sensor will now indicate 20 degrees AOA.

So, we see that as the aircraft pitches down the true AOA gradually decreases to zero degrees as long as a particular attitude is stabilized. Any AOA sensor with a constant positive error will therefore never reach a value of zero degrees in any constant pitch attitude between level flight and 90 degrees straight down.

I can add that this explanation is valid as long as the roll rate is zero or at least very low.

Edit: I have omitted some details, like a possibly angular deviation between the wing chord line and and the fuselage senterline and some other minor details. So if someone was going to be very pedantic (s)he could find some minor errors in my explanation, but the principle still holds true.

THIS! I appreciate your post(s) on this topic because you explained, elaborated, and offered some nuances. Yet you stayed within the subject matter without broad generalization about this tragic event, and avoided to cast blame one way or the other. Thanks Sir.
 
LTC8K6
Posts: 1452
Joined: Fri Jun 05, 2009 8:36 pm

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 2:40 pm

The AoA replacement must have been in the records. The pilots should have known it had been replaced recently.
 
beechnut
Posts: 686
Joined: Wed Apr 21, 2004 12:27 am

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 8:28 pm

PW100 wrote:
Perhaps the CoG was moved a little forward to improve drag efficiency (reduced tail loading).


It is the other was around. The tail generates negative, not positive, lift. Moving the CofG forward would require more negative lift from the tail to maintain the correct angle-of-attack, and would thus increase induced drag. An aft CofG unloads the tail, but makes the aircraft left stable and more difficult to recover from a stall. But it also makes it more fuel efficient as the lift and thus induced drag from the tail is less.

Beech
 
SteinarN
Posts: 110
Joined: Mon Dec 29, 2014 1:26 pm

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 8:44 pm

beechnut wrote:
PW100 wrote:
Perhaps the CoG was moved a little forward to improve drag efficiency (reduced tail loading).


It is the other was around. The tail generates negative, not positive, lift. Moving the CofG forward would require more negative lift from the tail to maintain the correct angle-of-attack, and would thus increase induced drag. An aft CofG unloads the tail, but makes the aircraft left stable and more difficult to recover from a stall. But it also makes it more fuel efficient as the lift and thus induced drag from the tail is less.

Beech


Exactly. I was thinking the same, Boeing has made the Max less front heavy, making the tail generating less downward force and then saved a couple tenths of a percent in fuel consumption.
Also this negative lift from the tail actually counts twice as the wings needs to make less (positive) lift too to counter the now reduced negative lift from the tail. And this causes an inherently less stable aircraft in the pitch attitude, as you correctly says. And to make the Max feel the same as the NG in manual flight mode and have the same type rating for the pilots Boeing had to give more power and authority to the automatic horizontal stabilizer trim compared to the NG. At least this is as I understand it.
 
dakota123
Posts: 125
Joined: Wed Aug 30, 2006 11:03 pm

Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 10:09 pm

SteinarN wrote:
beechnut wrote:
PW100 wrote:
Perhaps the CoG was moved a little forward to improve drag efficiency (reduced tail loading).


It is the other was around. The tail generates negative, not positive, lift. Moving the CofG forward would require more negative lift from the tail to maintain the correct angle-of-attack, and would thus increase induced drag. An aft CofG unloads the tail, but makes the aircraft left stable and more difficult to recover from a stall. But it also makes it more fuel efficient as the lift and thus induced drag from the tail is less.

Beech


Exactly. I was thinking the same, Boeing has made the Max less front heavy, making the tail generating less downward force and then saved a couple tenths of a percent in fuel consumption.
Also this negative lift from the tail actually counts twice as the wings needs to make less (positive) lift too to counter the now reduced negative lift from the tail. And this causes an inherently less stable aircraft in the pitch attitude, as you correctly says. And to make the Max feel the same as the NG in manual flight mode and have the same type rating for the pilots Boeing had to give more power and authority to the automatic horizontal stabilizer trim compared to the NG. At least this is as I understand it.


Apparently the Max is the only variant that ties AOA into the trim system, which may moot all of this. https://www.seattletimes.com/business/b ... directive/

(But an aft cg would require less of the trim system, not more. Less elevator movement would be required for the same desired action compared to a more forward cg. Actually, I could that see quicker-acting may be required, but not more authority.)

It’s interesting to me that the AD specifically notes that the cutout switches should remain in cutout for the remainder of the flight. Seems like an obvious thing that wouldn’t need to be said, unless there is a clue there as to what happened.
 
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PW100
Posts: 3115
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Re: FAA issues emergency 737 Max airworthiness order

Sat Nov 10, 2018 10:19 pm

SEPilot wrote:
Moving the CG forward would enhance stability, not decrease it. But without other changes the CG would have moved forward as the engines are heavier AND farther forward. To move the CG aft you need to shift weight to the tail.


beechnut wrote:
It is the other was around. The tail generates negative, not positive, lift. Moving the CofG forward would require more negative lift from the tail to maintain the correct angle-of-attack, and would thus increase induced drag. An aft CofG unloads the tail, but makes the aircraft left stable and more difficult to recover from a stall. But it also makes it more fuel efficient as the lift and thus induced drag from the tail is less.

Beech


Thanks guys. That's what I mean indeed (maybe should cut back on the late night posting).
Perhaps the Max traded some natural stability for efficiency.
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
acjbbj
Posts: 104
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Re: FAA issues emergency 737 Max airworthiness order

Sun Nov 11, 2018 4:09 am

The world needs a Dash 7 NextGen and Q200/Q300 NextGen!
Favourite plane: "L-1011-800 TriStar Next Generation" :mrgreen:
(3-Engine cargo jet approximately the size of a 77F, with three Trent XWB-97. Two engines on the wing, the third in the tail with an S-duct.)

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