pygmalion
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 5:44 pm

hivue wrote:
Disclaimer: Not an aeronautical engineer or involved in aviation.
The trimmable horizontal stabilizer wanting to jump in and pitch the nose down in the event it thinks AoA is excessive only when the autopilot is off sounds to me a lot like flight control law. How much alpha protection -- and other contemporary levels of automation (maybe a lot more in the case of the MAX) -- can be added to non-FBW airplanes without resulting in diminishing returns/a less safe airplane?


the system doesnt pitch the nose down directly like the pilot pushing forward on the column and moving the elevator. It is re-trimming the stabilizer and is clearly visible in the cockpit by watching the barber poled 8" diameter trim wheel by the pilot and copilot legs spin while its trimming the airplane. It dosnt go that fast... its not like the airplane is thrown into a dive.

https://www.youtube.com/watch?v=rxPa9A-k2xY
Last edited by pygmalion on Wed Nov 07, 2018 5:49 pm, edited 1 time in total.
 
SteinarN
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 5:48 pm

PW100 wrote:
Was the electrical disconnecting of STS already a memory item?


I too am very interested in the answer to this question. Anyone know the answer?
 
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Moose135
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 5:48 pm

pygmalion wrote:
the system doesnt pitch the nose down directly like the pilot pushing forward on the column and moving the elevator. It is re-trimming the stabilizer and is clearly visible in the cockpit by watching the barber poled 8" diameter trim wheel by the pilot and copilot legs spin while its trimming the airplane. It dosnt go that fast... its not like the airplane is thrown into a dive.

And 30 years ago, when I was flying KC-135s, we practiced runaway trim malfunctions in the simulator, so it shouldn't be a surprise when it happens.
KC-135 - Passing gas and taking names!
 
pygmalion
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 5:50 pm

Moose135 wrote:
pygmalion wrote:
the system doesnt pitch the nose down directly like the pilot pushing forward on the column and moving the elevator. It is re-trimming the stabilizer and is clearly visible in the cockpit by watching the barber poled 8" diameter trim wheel by the pilot and copilot legs spin while its trimming the airplane. It dosnt go that fast... its not like the airplane is thrown into a dive.

And 30 years ago, when I was flying KC-135s, we practiced runaway trim malfunctions in the simulator, so it shouldn't be a surprise when it happens.


Trim malfunctions are a normal sim training item... so yes I agree.
 
pygmalion
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 5:59 pm

here is a runaway trim training video in a 737 simulator...

http://www.youtube.com/watch?v=3pPRuFHR1co
 
BravoOne
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 6:09 pm

SteinarN wrote:
PW100 wrote:
Was the electrical disconnecting of STS already a memory item?


I too am very interested in the answer to this question. Anyone know the answer?


It's been a memory item going back as far is the first 707's. nothing new here to see, and I suspect those who really know are not talking while others demonstrate their lack of knowledge on the totality of this subject.
 
QuickSilverNG
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 6:15 pm

SomebodyInTLS wrote:
log0008 wrote:
uta999 wrote:
Perhaps a simple App on an iPad (based on SatNav) satellite data could be created, that gives (approx) airspeed and an artificial horizon, and then outputs both to a small HUD in between the pilots.


GPS ground speed has nothing to do with airspeed


I think we need to have a new a.net emoticon of someone holding this as a banner...


This and tail coming off are two things I learnt about aviation from this thread. Thanks to all those that share.
 
stratclub
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 6:33 pm

Trin wrote:
stratclub wrote:
Erebus wrote:
Interesting development. Question I have is, if such issues have surfaced on other MAXes flying even if they were not immediately detected, or if this particular Lion Air aircraft presented the first known instance of such a problem.

Holy crap. No issues has been officially identified yet. The supposed source for this fake news remained anonymous. If people buy into unsubstantiated fake news the journalist's payday is assured. Watch for the slim possibility of a teeny tiny retraction on the last page if the reporting was not factual and correct.


FACT: Boeing have issued an Operations Bulletin addressing the issues (mentioned in this article and many others across media this morning) that they are positing contributed to this incident.

FACT: The more times you say "fake news" in a post, the less serious you will be taken. There's actually probably an algorithm out there that deals with this that perhaps some of our more technical-minded members can provide you with.

Trin

I did make an assumption based on just one article that quoted an anonymous source for questionable information. My bad. With further reading it does occur to me that a runaway stab trim could very easily have caused the crash. https://www.youtube.com/watch?v=3pPRuFHR1co
 
wingman
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 6:42 pm

pygmalion wrote:
here is a runaway trim training video in a 737 simulator...

http://www.youtube.com/watch?v=3pPRuFHR1co


Thanks for all the video link, very helpful to see what everyone is talking about. I'm well late to posting anything here and understand the toddlers (christ I must be getting old) in the link above knew in advance what the scenario would be, but wouldn't the Lion Air pilots have been expecting the same situation after the four prior flights? Something seems wrong in the MAX flight control set-up (or something was installed improperly in that particular plane) and yet the recovery procedure from the error looks as easy as flipping that trim switch off.
 
BREECH
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 6:44 pm

Hearing all this "they should work on this in a simulator", I have a question. Just how much do you (or "they") think a human being can remember and automatically implement in a critical situation? EVERY time (or at least VERY often) when a plane crashes there is something the pilots didn't practice in a simulator. BUT!!! How useful this "training" can be. I just cannot imagine they can memorize (let alone automate) all the possible scenarios. Pilots are not some superhumans with the brains of a T1000. They are regular people who miss things, forget things, don't pay attention. Say you buy yourself a very fast car. Do you go into a simulator and work on your "sudden tire pressure loss"? It can cause A LOT of trouble if it happens on a high speed road, like an autobahn. So why do we expect pilots to remember every single piece of training they ever received? And why we almost never blame the airplane manufacturer for not creating an error-free system? They have thousands of engineers and test-pilots to do that. Yet there are only two normal regular people in the cockpit who have to somehow remember all their negligences.
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hivue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 7:07 pm

pygmalion wrote:
Moose135 wrote:
pygmalion wrote:
the system doesnt pitch the nose down directly like the pilot pushing forward on the column and moving the elevator. It is re-trimming the stabilizer and is clearly visible in the cockpit by watching the barber poled 8" diameter trim wheel by the pilot and copilot legs spin while its trimming the airplane. It dosnt go that fast... its not like the airplane is thrown into a dive.

And 30 years ago, when I was flying KC-135s, we practiced runaway trim malfunctions in the simulator, so it shouldn't be a surprise when it happens.


Trim malfunctions are a normal sim training item... so yes I agree.


But the present case doesn't sound like a runaway trim situation or a trim malfunction. It sounds like some computer was programmed to purposely trim nose down for alpha protection and it did just what it was programmed to do. The only problem is that it's looking like it was, for some reason, acting on bad AoA information. My question was whether this level and type of implementation of envelope protection is appropriate on a non-FBW airplane.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
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Moose135
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 7:35 pm

BREECH wrote:
Hearing all this "they should work on this in a simulator", I have a question. Just how much do you (or "they") think a human being can remember and automatically implement in a critical situation?

You spend most of your time in the simulator practicing malfunctions - engine loss on takeoff, system failures, runaway trim - so when they happen in the airplane, it becomes a natural reaction, a "muscle memory" sort of thing. At the end of the day, there aren't a lot of situations where you need to react quickly and correctly from memory only, and you work on those over and over in the sim.
KC-135 - Passing gas and taking names!
 
iamlucky13
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 7:58 pm

hivue wrote:
pygmalion wrote:
Moose135 wrote:
And 30 years ago, when I was flying KC-135s, we practiced runaway trim malfunctions in the simulator, so it shouldn't be a surprise when it happens.


Trim malfunctions are a normal sim training item... so yes I agree.


But the present case doesn't sound like a runaway trim situation or a trim malfunction. It sounds like some computer was programmed to purposely trim nose down for alpha protection and it did just what it was programmed to do. The only problem is that it's looking like it was, for some reason, acting on bad AoA information. My question was whether this level and type of implementation of envelope protection is appropriate on a non-FBW airplane.


I'm unclear why you're describing this as alpha protection and not a trim malfunction. It sounds like the computer was programmed to maintain a preferred AoA, not prevent an inappropriate AoA.

It does indeed seem to be the case it was acting on bad AoA info. Bad data is a problem regardless of whether you have a FBW aircraft, although the exact implications are different for each.
 
kalvado
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:00 pm

How about a combination of unreliable airspeed and runaway trim?
There is a lot of "power and pitch" information as a way to handle airspeed issues; but adding trim runaway on top of that - would it become a bit more fun to handle?
Or is there anything with autothrottle in terms of alpha protection what can also kick in?
 
rheinwaldner
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:02 pm

BravoOne wrote:
SteinarN wrote:
PW100 wrote:
Was the electrical disconnecting of STS already a memory item?


I too am very interested in the answer to this question. Anyone know the answer?


It's been a memory item going back as far is the first 707's. nothing new here to see, and I suspect those who really know are not talking while others demonstrate their lack of knowledge on the totality of this subject.

Then why does Boeing send a bulletin only to the MAX operators?
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smartplane
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:05 pm

I have an inherent problem with grandfathering, because knowledge is 'lost' with each generation and iteration, including what were at the time, logical assumptions.

Over 25 years ago, I was contracted to an accounting firm to 'improve' a clients processes and staffing. The accounting firm had developed a software based staffing model, originally on a mid-size computer, then migrated to PC, which had many iterations developed and overlaid. And it seemed every change, assumed previous work was correct, so only the new was tested.

Alarm bells rang when staff from a firm that had recently undertaken a peer review / audit of the software, were unable to answer specific 'what if' questions.

So we tested a few smaller customer locations, layer by layer. The model had no commonsense rules, for example recommending customer sites could operate with fractions of staff (FTEU), when two was the practical minimum. But worse, it calculated staff reductions based on the starting number, for every iteration.

The company had 'got away' with this because they were dealing with big sites, and had not been able to implement all options / iterations, but if you did apply all options, locations were projected to operate with negative staff numbers.

It wasn't difficult to rectify, but until the perfect storm arose, and every factor (option in this case) applied, the defect wasn't detected.

Irrespective of the reasons for the Lion accident, commercial aviation grandfathering should change. Grandfathering is high risk for structure, but unacceptable for software. Change should be defined, and when change greater than X% occurs, grandfathering should be lost. No negotiation, no lobbying, lost.
 
cat3appr50
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:10 pm

Since one of the AoA sensors provided incorrect readings per the “Operations Manual Bulletin to all Boeing 737 Max Operators” regarding the JT610 accident, it would then seem logical that an AoA sensor is a/the root cause. So, what was the root cause of the sensor providing incorrect readings? Was one of the AoA sensors damaged (or repaired) at some point in the past? Was the specific AoA sensor angular position OK but it’s specific output signal (i.e. calibration) was in error? Was the AoA sensor output OK but the associated ADIRU which received the AoA output signal dysfunctional for some reason and then passed an erroneous output forward, resulting in a false stall condition, which then set in motion the trim nose down automatic response cycle? Is this a potential issue with the 737 NG (700, 800, 900) fleet, or solely confined to the 737 Max 8? If it is just the Max 8, then what does the Max 8 have in AoA hardware/software that is different from the NG’s?

Per the same noted Bulletin, “pilots are reminded that an erroneous AoA can cause some or all of the following indications and effects”…noting just one of them, an “AoA Disagree Alert (if the AoA Indicator Option is Installed).” Now why would any airline not want the option of knowing when a AoA disagree (between the L and R AoA) condition occurs, since it could potentially lead to the automatic trim nose down (challenging) cycle reacting to (by software design) that a stall then must be occurring, along with a plethora of other indications/warnings being initiated as well. I would want to know the root problem asap…”AoA Disagree”…and that is the root cause of why as a pilot one is getting the automatic trim nose down scenario, an intermittent stick shaker, etc. Otherwise, one is getting alarms for “IAS Disagree”, “Alt Disagree”, “Feel Diff Press”, and an “intermittent stick shaker”, etc., creating a first reaction that there is likely an issue with the pitot system (UAS), when in reality it is the AoA system. And unless you have purchased the “option” you’re not going to get that critical root cause AoA disagree indication. IMO the AoA indicator on the PFD needs to be on both the Captain and FO PFD, L AoA on Captains side and R AoA on the FO side so that the disagree can be seen (trending). Just my opinion.
 
hivue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:43 pm

iamlucky13 wrote:
It sounds like the computer was programmed to maintain a preferred AoA, not prevent an inappropriate AoA.


If that's how it works then I see your point. But if what it really was trying to do is keep the airplane from stalling then I would think it could be called some form of "protection."
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
Eikie
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 8:59 pm

dragon6172 wrote:
7BOEING7 wrote:
CeddP wrote:
Does that even apply to STS operation ? At acceleration altitude for exemple, as you push control column to decrease pitch and accelerate, you always have the STS annoyingly trimming nose up until trimming nose down yourself with trim switches… I reckon the forward movement of the column is quite subtle, but it makes me wonder if the "anti-runaway" feature apply to STS operation ?


Boeing is referencing that procedure in the bulletin.

Assuming full nose down trim, can you hold the aircraft level with just aft control column pressure? If so, any guesses on the force required to do so?

Easily possible. It's annoying, but perfect flyable.
 
SteinarN
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:27 pm

hivue wrote:
iamlucky13 wrote:
It sounds like the computer was programmed to maintain a preferred AoA, not prevent an inappropriate AoA.


If that's how it works then I see your point. But if what it really was trying to do is keep the airplane from stalling then I would think it could be called some form of "protection."


The system cant possibly try to maintain a specific angle of attack except trying to avoid an angle of attack which is so high that it means the aircraft is stalled, that is keeping the angle of attack below something like 10 degrees or thereabout. During normal flight the angle of attack is something like 2 degrees at low altitude, higher at low speed and higher at high altitude, and is dependent on aircraft weight, speed, density of the air and G, and NOT dependent and do not vary with aircraft attitude or rate of climb or decent.

So, there is a lot of unanswered questions here. This was obviously not as simple for the pilots as a pure trim runaway. They got other faults or symptoms too, or even first, like speed disagree, possibly autopilot disconnect, possibly stick shaker etc.

But in all this - there seems to be two angle of attack sensors - but how on earth can the systems be designed such that when those two sensors disagree on the actual angle of attack and the system has no way to know which sensor is correct, it then still starts to massively run the horizontal electric trim according to the faulty sensor and disregarding the one correct sensor? Or does it add in the possibly faulty speed readings from the pitot system into the mix to shore up the faulty AoA sensor reading?

I was very very critical regarding the performance of the AF447 pilots, but this time I wont blame the Lion Air pilots one bit with the information we have got so far.
 
zakelwe
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:32 pm

How often are planes allowed to continue flying when they have both airspeed and trim issues and the cause is not determined but instead a "trial and error " solution tried more than once?

Seems odd to me also that control software has an extra feature for manual control but then if this goes wrong it does not have an automatic solution but a manual one that needs to be known/done. That seems to degrade the safety net of having the extra level of protection in the first place.

The CVR needs to be recovered as the human side is needed to complete this complex interaction of events.
 
djm18
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:39 pm

Again, interesting to note the AoA instrument issues on the last flight prior to the accident as noted in the article below. It seems the crew did an amazing job in handling this situation on a night flight.


https://www.channelnewsasia.com/news/as ... s-10905532

Soerjanto Tjahjono, head of Indonesia's National Transportation Safety Committee told reporters that after one flight from Bali to Jakarta - the last flight before the crash - the left and right AOA sensors were found to disagree by 20 degrees.

He said the pilot had landed the plane safely on that occasion.

"The pilot's success became our reference to give a recommendation to Boeing so they could issue an advice for other airlines to follow the same procedures if the same situation occurs," Soerjanto said.

Read more at https://www.channelnewsasia.com/news/as ... s-10905532
 
Trin
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:41 pm

SteinarN wrote:

I was very very critical regarding the performance of the AF447 pilots, but this time I wont blame the Lion Air pilots one bit with the information we have got so far.


Agreed 100% Whereas AF447 was complete failure to respond to standard loss of airspeed information at high altitude (and subsequent nose-up inputs by the PF occurring continually until the aircraft was stalled, AND non-realization of that by ANY of the three crew all the way to impact with the ocean surface) - this case seems vastly different. Not least of which in that the aircraft apparently had inherent technical issues that had persisted for DAYS (and had, apparently, not been rectified correctly by maintenance crews on numerous occasions), and the fact that whatever technical issues the aircraft DID have were manifesting themselves at very sensitive segments of the flight (i.e. immediately post-takeoff and at climb-out).

It boggles my mind what the crew were going through at climb-out, with POSSIBLY loss of airspeed data, POSSIBLY faulty AoA sensor and/or the data it was sending, POSSIBLY any number of stall/overspeed warnings, POSSIBLY a very startling and rapid descent immediately after takeoff (per the FR24 data), and POSSIBLY having the aircraft continue to try to trim downwards during all of this. With only ~5,000 ft of altitude.

Something was very wrong with this airplane. I just continue to try and keep the families of the victims in my thoughts.

Trin
Last edited by Trin on Wed Nov 07, 2018 9:43 pm, edited 1 time in total.
 
SteinarN
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:42 pm

A technical write up from Leeham News by Bjørn Fehrm:
https://leehamnews.com/2018/11/07/boein ... -accident/
 
SteinarN
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 9:55 pm

Trin wrote:
SteinarN wrote:

I was very very critical regarding the performance of the AF447 pilots, but this time I wont blame the Lion Air pilots one bit with the information we have got so far.


Agreed 100% Whereas AF447 was complete failure to respond to standard loss of airspeed information at high altitude (and subsequent nose-up inputs by the PF occurring continually until the aircraft was stalled, AND non-realization of that by ANY of the three crew all the way to impact with the ocean surface) - this case seems vastly different. Not least of which in that the aircraft apparently had inherent technical issues that had persisted for DAYS (and had, apparently, not been rectified correctly by maintenance crews on numerous occasions), and the fact that whatever technical issues the aircraft DID have were manifesting themselves at very sensitive segments of the flight (i.e. immediately post-takeoff and at climb-out).

It boggles my mind what the crew were going through at climb-out, with POSSIBLY loss of airspeed data, POSSIBLY faulty AoA sensor and/or the data it was sending, POSSIBLY any number of stall/overspeed warnings, POSSIBLY a very startling and rapid descent immediately after takeoff (per the FR24 data), and POSSIBLY having the aircraft continue to try to trim downwards during all of this. With only ~5,000 ft of altitude.

Something was very wrong with this airplane. I just continue to try and keep the families of the victims in my thoughts.

Trin


Exactly. In the AF447 case the pilots could have done absolutely nothing, keept their hands off of the sidestick and the aircraft would have continued flying flawlessly and stable. The pitot static would have opened up again, as it in fact did, and everything would have been ok.

But in this case the aircraft itself seems to have been hell bent on plunging straight to the ground from a low altitude, repeatedly. The crew on the previous flight did a great job saving the plane and all on board, the last crew not so lucky or skilfull.

It will be very interesting learning more facts about exactly what was going on in the plane and why. I think there is still a lot of unanswered questions.
 
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PW100
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 10:16 pm

kalvado wrote:
How about a combination of unreliable airspeed and runaway trim?
There is a lot of "power and pitch" information as a way to handle airspeed issues; but adding trim runaway on top of that - would it become a bit more fun to handle?
Or is there anything with autothrottle in terms of alpha protection what can also kick in?

This.

The crew may have been working the unreliable airspeed checklist, trying to understand what was going on. Then, when on manual control, BAM another issue: STS runaway, which they may not have recognized as such immediately, as their mind set may have been with unreliable air speed --> pitch and power. At 5000 ft, 300 kts, they did not have much time to do the right thing.
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PW100
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 10:20 pm

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83EC7F95F3E5BFBD8625833E0070A070?OpenDocument

BTW, I find it "interesting" that the AD only covers 737-8 and -9. Not the -800 series. Would that suggest inherent differences between these families in terms of flight control system, logic, or operating manual? Might there be something that doesn't apply to the previous generation series?
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
edmountain
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:01 pm

PW100 wrote:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83EC7F95F3E5BFBD8625833E0070A070?OpenDocument

BTW, I find it "interesting" that the AD only covers 737-8 and -9. Not the -800 series. Would that suggest inherent differences between these families in terms of flight control system, logic, or operating manual? Might there be something that doesn't apply to the previous generation series?


Not a pilot, so please excuse me if this is a dumb question.

The AD says:

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 of the horizontal stabilizer.


and

In the event of an uncommanded horizontal stabilizer trim movement, combined with any of the following potential effects or indications resulting from an erroneous Angle of Attack (AOA) input, the flight crew must comply with the Runaway Stabilizer procedure in the Operating Procedures chapter of this manual:


I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?
 
XT6Wagon
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:01 pm

PW100 wrote:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83EC7F95F3E5BFBD8625833E0070A070?OpenDocument

BTW, I find it "interesting" that the AD only covers 737-8 and -9. Not the -800 series. Would that suggest inherent differences between these families in terms of flight control system, logic, or operating manual? Might there be something that doesn't apply to the previous generation series?


I read this AD not as new information, but more of a "hey stupid, standard procedures are still standard. Ignoring them results in bad things".
 
SteinarN
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:10 pm

edmountain wrote:
I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?

:checkmark:
I too are very interested in knowing the logic behind this design decision. Or do the apparently faulty air speed data also play a role in this situation?
 
hivue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:16 pm

edmountain wrote:
Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?


This would strike me as analogous to a degraded flight control law -- except the 737 is not a FBW airplane.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
pygmalion
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:25 pm

PW100 wrote:
kalvado wrote:
How about a combination of unreliable airspeed and runaway trim?
There is a lot of "power and pitch" information as a way to handle airspeed issues; but adding trim runaway on top of that - would it become a bit more fun to handle?
Or is there anything with autothrottle in terms of alpha protection what can also kick in?

This.

The crew may have been working the unreliable airspeed checklist, trying to understand what was going on. Then, when on manual control, BAM another issue: STS runaway, which they may not have recognized as such immediately, as their mind set may have been with unreliable air speed --> pitch and power. At 5000 ft, 300 kts, they did not have much time to do the right thing.


Fly the airplane... then troubleshoot. If you have problems, the pilot flying... flies the airplane. Autopilot off, flying to nominal throttle and pitch attitudes if needed. The pilot not flying, assists with navigation and communication. Then the pilot not flying troubleshoots. That's how it works. Basic CRM. Unreliable airspeed is a memory check list item. So is runaway trim.

There are three separate airspeed systems. Two separate AOA systems. If they disagree, you are taught to fly attitude and throttle and ignore them. keep the airplane stable and then work it out after. If the trim is moving uncommanded, grab the trim wheel to stop it and hit the stab trim cutoff and fly the airplane. RTB.

"runaway" stab trim is not a BAM. The airplane noses over and pushes against pilot holding the control wheel. It doesnt invert airplane and roll it over.

There is radar altimeter data at 5,000 feet. There is an HSI to determine pitch attitude that doesnt need the pitot/static system. If really needed, there is a manual compass you can use for attitude.

This is standard training and part of annual recurring training. The pilots are not told in the simulator what issues they will face. They are taught to notice the problem and then react. Again, it is something they train for.

Remember, a commercial airline pilot has a ATP certificate that requires 1,500 hours of flight time to get.
 
dragon6172
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:46 pm

None of this discussion of trim problems explains the dive into the ocean. The problem showed on climb-out, they leveled at 5000 and flew there for 6-7 minutes, probably dealing with the problem judging by the altitude deviations. And then they just let go of the controls and let the plane fly itself into the ocean? Doesn't make any sense.
Phrogs Phorever
 
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glideslope
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Wed Nov 07, 2018 11:52 pm

dragon6172 wrote:
konrad wrote:
I find it strange that conditions for such an important malfunction have not occurred earlier, in test flying or in any of the hundreds of daily 737 MAX flights.

It has come up on prior flights. The flight right before the accident flight actually. Those pilots were able to follow the procedure and continue the flight.


Yes they were. I feel a lot will be revealed on the CVR. Not arm chairing, just extremely interested to hear the CRM during this tragic loss of life.
To know your Enemy, you must become your Enemy.” Sun Tzu
 
pygmalion
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 12:07 am

SteinarN wrote:
edmountain wrote:
I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?

:checkmark:
I too are very interested in knowing the logic behind this design decision. Or do the apparently faulty air speed data also play a role in this situation?


The automated stab trim system is there to reduce pilot work load and reduce control forces. In an airplane without an automated trim system, the pilot has to manually move the trim to keep from having to hold the control wheel to maintain stable flight. With an automated trim system, the system continuously trims the airplane to keep the controls centered in the requested pitch attitude just like a pilot would if they were flying a manually trimmed airplane. If the pilot is flying autopilot off, the system still trims the airplane to maintain a constant angle of attack. This reduces pilot work load as they dont have to do it manually. All pilots know how to trim an airplane manually. its how they are taught from their very first flight in a Cessna 172. If the trim system "runs away" or over trims the airplane, the pilot shuts it off and manually trims the airplane or just flies the airplane out of trim. It will fly out of trim, the controls are just heavy on one direction.

There are definitely notifications, cautions, warnings to the pilots if the pitot static or the AOA systems disagree or if there is a trim warning.
 
edmountain
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 12:31 am

pygmalion wrote:
SteinarN wrote:
edmountain wrote:
I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?

:checkmark:
I too are very interested in knowing the logic behind this design decision. Or do the apparently faulty air speed data also play a role in this situation?


The automated stab trim system is there to reduce pilot work load and reduce control forces. In an airplane without an automated trim system, the pilot has to manually move the trim to keep from having to hold the control wheel to maintain stable flight. With an automated trim system, the system continuously trims the airplane to keep the controls centered in the requested pitch attitude just like a pilot would if they were flying a manually trimmed airplane. If the pilot is flying autopilot off, the system still trims the airplane to maintain a constant angle of attack. This reduces pilot work load as they dont have to do it manually. All pilots know how to trim an airplane manually. its how they are taught from their very first flight in a Cessna 172. If the trim system "runs away" or over trims the airplane, the pilot shuts it off and manually trims the airplane or just flies the airplane out of trim. It will fly out of trim, the controls are just heavy on one direction.

There are definitely notifications, cautions, warnings to the pilots if the pitot static or the AOA systems disagree or if there is a trim warning.

Yes, but why would the system be allowed to continue to cause uncommanded trim movements when it is known that the data it's responding to are erroneous?
Last edited by edmountain on Thu Nov 08, 2018 12:53 am, edited 1 time in total.
 
salttee
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 12:46 am

My assumption is that pulling back on the control column on this 737 will cause the elevators to override any errant trim applied by the flight-control system. Therefore, the bulletin from Boeing is not addressing the cause of the crash of JT610.

Agreed?
 
dtwpilot225
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 12:49 am

I’m reading a lot of of they should have done this or that and flying the airplane with full trim up or down is easy, let’s stop right there; they may be designed to work that way but it ain’t easy in the least bit. It would take an incredible amount of control force it to hold an airplane level with full trim down or up. And yes there are procedures to disconnect a runaway trim wheel, but if the pilots were getting false info, they might have been focused on that and not noticed the trim right away. Should they have been able to recover from this? Probably. Should it have been easy? Hell no
 
dragon6172
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 1:08 am

pygmalion wrote:
SteinarN wrote:
edmountain wrote:
I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?

:checkmark:
I too are very interested in knowing the logic behind this design decision. Or do the apparently faulty air speed data also play a role in this situation?


The automated stab trim system is there to reduce pilot work load and reduce control forces. In an airplane without an automated trim system, the pilot has to manually move the trim to keep from having to hold the control wheel to maintain stable flight. With an automated trim system, the system continuously trims the airplane to keep the controls centered in the requested pitch attitude just like a pilot would if they were flying a manually trimmed airplane. If the pilot is flying autopilot off, the system still trims the airplane to maintain a constant angle of attack. This reduces pilot work load as they dont have to do it manually. All pilots know how to trim an airplane manually. its how they are taught from their very first flight in a Cessna 172. If the trim system "runs away" or over trims the airplane, the pilot shuts it off and manually trims the airplane or just flies the airplane out of trim. It will fly out of trim, the controls are just heavy on one direction.

There are definitely notifications, cautions, warnings to the pilots if the pitot static or the AOA systems disagree or if there is a trim warning.


Speed Trim System works to return the aircraft to trimmed airspeed. It takes inputs from throttle position, stabilizer position, airspeed, and vertical speed. When the airspeed deviates from the trimmed airspeed the STS moves the stabilizer to return the aircraft to the trimmed airspeed. This means the aircraft will climb or descend until the trimmed airspeed is reached, at which point the STS moves the stabilizer back to the trimmed position (reduced control forces).

This is why pilots say that the STS is trimming the wrong way. If the aircraft is straight and level trimmed and encounters something that causes an airspeed increase, the STS will trim a climb to decrease airspeed to the trimmed position. A pilot manually flying the aircraft detects a climb will want to trim the opposite direction to maintain altitude.

This description is for NGs. Haven't found any info on how the MAX differs.
Phrogs Phorever
 
benjjk
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 2:13 am

My friend is a 737 driver who forwarded a communique from his chief pilot. It says:

"There is no intention to extend the OMB to the 737NG, however many of you are likely wondering why it does not apply to these variants. The OMB describes a scenario where erroneous Angle of Attack (AOA) data causes the pitch trim system to trim the stabilizer down in increments lasting up to 10 seconds each. The pitch trim system is responding to a pre-programed speed trim schedule required to comply with FAR requirements. While the basic architecture of the 737 MAX variants (designated 737-8/9, as opposed to the NG variants which are designated -800/900) is very similar to the NG, there are some pertinent differences “under the hood.” This is particularly true of the speed trim system, which has expanded authority beyond that available to the NG variants to activate during manual flight – this is because of differences in the longitudinal stability of the 737 MAX. "
 
mandala499
Posts: 6498
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 2:46 am

edmountain wrote:
I'm curious why the system would be allowed to cause "uncommanded horizontal stabilizer trim movement" when the data are known (or suspected) by the system to be erroneous. Would it not be safer to have the system reject the data, not cause uncommanded trim movements, and raise an alert to the pilots about the unreliable data?

I really want to know what can cause the STS nosedown trim in unreliable airspeed... Toxic data from ADR? or?
Not familiar with the setup...

glideslope wrote:
Yes they were. I feel a lot will be revealed on the CVR. Not arm chairing, just extremely interested to hear the CRM during this tragic loss of life.

I'm sure a LOT would be revealed, including CRM deficiencies... and a lot of arm chairing too by many others.

dtwdpilot225 wrote:
I’m reading a lot of of they should have done this or that and flying the airplane with full trim up or down is easy, let’s stop right there; they may be designed to work that way but it ain’t easy in the least bit. It would take an incredible amount of control force it to hold an airplane level with full trim down or up. And yes there are procedures to disconnect a runaway trim wheel, but if the pilots were getting false info, they might have been focused on that and not noticed the trim right away. Should they have been able to recover from this? Probably. Should it have been easy? Hell no

Agree... on their own, UAS or runaway trim, should be a "no sweat"... but as a combo? I think it's a different story altogether... If it was easy, the bulletin wouldn't end up with an EAD on top of it.

dragon6172 wrote:
Speed Trim System works to return the aircraft to trimmed airspeed. It takes inputs from throttle position, stabilizer position, airspeed, and vertical speed. When the airspeed deviates from the trimmed airspeed the STS moves the stabilizer to return the aircraft to the trimmed airspeed. This means the aircraft will climb or descend until the trimmed airspeed is reached, at which point the STS moves the stabilizer back to the trimmed position (reduced control forces).

Does this mean STS would be allowed to take in toxic data from the ADR? If so, I wonder there isn't a way to stop STS from taking toxic data in the event of an ADR fault or unreliable airspeed? To me sounds like asking uncessary workload during unreliable airspeed. :( (Of course, hindsight, is always 20/20)

benjjk wrote:
This is particularly true of the speed trim system, which has expanded authority beyond that available to the NG variants to activate during manual flight – this is because of differences in the longitudinal stability of the 737 MAX.

I hereby declare that I hate the new Boeing FCOMs that don't explain the systems in detail unlike the days of the 737-200 manuals. I hate this "it's under the hood, you don't need to know the details" kinda thing... Just a personal opinion...
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
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Starlionblue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:04 am

Amiga500 wrote:
trpmb6 wrote:
I believe you just described the Airbus Backup Speed Scale system. (BUSS) that has been discussed here.

I'm not familiar with how the Airbus BUSS system works, but I assume it involves measuring angle of attack by determining the angle of the streamline with the wing. (cough - by definition that would be angle of attack :mrgreen: ) Probably have naca scoops on the wing or some other method. I may post in the technical forum about this topic just to get a better understanding personally.


That sounds like it runs through some convoluted process to infer speed.

I'm talking about simple stuff - AoA only - and should be constantly displayed. Wouldn't be hard to add a blip to the artificial horizon or maybe cleaner, a vertical scale running beside it.


BUSS is quite simple actually. It uses raw AoA from the vanes. There is no speed displayed, just an AoA range. Just keep it in the green. Combine with an appropriate thrust setting and you get expected performance.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Starlionblue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:12 am

pygmalion wrote:
PW100 wrote:
kalvado wrote:
How about a combination of unreliable airspeed and runaway trim?
There is a lot of "power and pitch" information as a way to handle airspeed issues; but adding trim runaway on top of that - would it become a bit more fun to handle?
Or is there anything with autothrottle in terms of alpha protection what can also kick in?

This.

The crew may have been working the unreliable airspeed checklist, trying to understand what was going on. Then, when on manual control, BAM another issue: STS runaway, which they may not have recognized as such immediately, as their mind set may have been with unreliable air speed --> pitch and power. At 5000 ft, 300 kts, they did not have much time to do the right thing.


Fly the airplane... then troubleshoot. If you have problems, the pilot flying... flies the airplane. Autopilot off, flying to nominal throttle and pitch attitudes if needed. The pilot not flying, assists with navigation and communication. Then the pilot not flying troubleshoots. That's how it works. Basic CRM. Unreliable airspeed is a memory check list item. So is runaway trim.

There are three separate airspeed systems. Two separate AOA systems. If they disagree, you are taught to fly attitude and throttle and ignore them. keep the airplane stable and then work it out after. If the trim is moving uncommanded, grab the trim wheel to stop it and hit the stab trim cutoff and fly the airplane. RTB.

"runaway" stab trim is not a BAM. The airplane noses over and pushes against pilot holding the control wheel. It doesnt invert airplane and roll it over.

There is radar altimeter data at 5,000 feet. There is an HSI to determine pitch attitude that doesnt need the pitot/static system. If really needed, there is a manual compass you can use for attitude.

This is standard training and part of annual recurring training. The pilots are not told in the simulator what issues they will face. They are taught to notice the problem and then react. Again, it is something they train for.

Remember, a commercial airline pilot has a ATP certificate that requires 1,500 hours of flight time to get.


Good points. A couple of corrections though:
- Recurrent Training is typically with known scenarios. You know what will happen, at least in general, because there are things to be “checked off” in that particular session. Simulator sessions where the pilots don’t know what will happen would be things like conmand LOFTs.
- The 1500 hour and ATP requirement is a US thing. In the rest of the world airliners are routinely crewed by pilots with CPLs and 500 hours. Also, even a guy with 2000 hours might have 1800 in light pistons which are very different from swept wing jets.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Erebus
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:14 am

Does anyone know what the JT610 flight number has been replaced with on this route?
 
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Starlionblue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:18 am

BREECH wrote:
Hearing all this "they should work on this in a simulator", I have a question. Just how much do you (or "they") think a human being can remember and automatically implement in a critical situation? EVERY time (or at least VERY often) when a plane crashes there is something the pilots didn't practice in a simulator. BUT!!! How useful this "training" can be. I just cannot imagine they can memorize (let alone automate) all the possible scenarios. Pilots are not some superhumans with the brains of a T1000. They are regular people who miss things, forget things, don't pay attention. Say you buy yourself a very fast car. Do you go into a simulator and work on your "sudden tire pressure loss"? It can cause A LOT of trouble if it happens on a high speed road, like an autobahn. So why do we expect pilots to remember every single piece of training they ever received? And why we almost never blame the airplane manufacturer for not creating an error-free system? They have thousands of engineers and test-pilots to do that. Yet there are only two normal regular people in the cockpit who have to somehow remember all their negligences.


You have a point. However pilot training is designed to repeatedly expose you to critical scenarios. The more likely and critical, the more often you see it.

Procedures are also designed so that memory items are kept to a minimum. Stabilise the aircraft, then reference a printed or on screen procedure. We are taught methods of dealing with situations, and we practice applying these methods.

The logic is that if you get something you’ve never seen you can used your knowledge and your methods to deal with it.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
maint123
Posts: 36
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:21 am

Too many people concentrating on how the pilots should have recovered from a faulty plane rather than what the fault was in a new plane.
1. In manual mode why still have a feature in which the auto trimming comes into play ?
2. Boeing being quite Cryptic about the differences in the software in max series wrt the other 737s.
3. Again the same query , when a plane is at 5000 ft , flying at 700 to 800 ft per sec , would a pilot struggling to keep a plane level in manual , have enough time (5 to 6 secs)to implement any solutions for a sudden and massive dip in the plane?
4. A maintenance engineer was flying in the plane so the pilots were very well aware of the previous flights issues , so was not a bolt out of the blue.
5. Let's stop hoping that its a pilot or maintenance issue so that the boeing company can come out of the crash smelling like roses , and just concentrate on the information available for any conclusions.
6. And for the question why only this plane had a issue not others , in car crashes only a low decimal percent crashes lead to recall of 100s of thousands of cars, no one waits for the figures to rise to thousands before taking action.
 
mandala499
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:23 am

The flight number continued until 31Oct.
Since, JT610 has been replaced with JT216.
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
hivue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:36 am

benjjk wrote:
there are some pertinent differences “under the hood.” This is particularly true of the speed trim system, which has expanded authority beyond that available to the NG variants to activate during manual flight – this is because of differences in the longitudinal stability of the 737 MAX. "


I'm still wondering whether, with the MAX, Boeing was trying to get as much FBW-type behavior as they could out of a non-FBW airplane.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
dragon6172
Posts: 928
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:43 am

maint123 wrote:
Too many people concentrating on how the pilots should have recovered from a faulty plane rather than what the fault was in a new plane.
1. In manual mode why still have a feature in which the auto trimming comes into play ?

FAR requirement for longitudinal stability
Phrogs Phorever
 
osiris30
Posts: 2373
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangal Pinang

Thu Nov 08, 2018 3:55 am

SteinarN wrote:
Trin wrote:
SteinarN wrote:

I was very very critical regarding the performance of the AF447 pilots, but this time I wont blame the Lion Air pilots one bit with the information we have got so far.


Agreed 100% Whereas AF447 was complete failure to respond to standard loss of airspeed information at high altitude (and subsequent nose-up inputs by the PF occurring continually until the aircraft was stalled, AND non-realization of that by ANY of the three crew all the way to impact with the ocean surface) - this case seems vastly different. Not least of which in that the aircraft apparently had inherent technical issues that had persisted for DAYS (and had, apparently, not been rectified correctly by maintenance crews on numerous occasions), and the fact that whatever technical issues the aircraft DID have were manifesting themselves at very sensitive segments of the flight (i.e. immediately post-takeoff and at climb-out).

It boggles my mind what the crew were going through at climb-out, with POSSIBLY loss of airspeed data, POSSIBLY faulty AoA sensor and/or the data it was sending, POSSIBLY any number of stall/overspeed warnings, POSSIBLY a very startling and rapid descent immediately after takeoff (per the FR24 data), and POSSIBLY having the aircraft continue to try to trim downwards during all of this. With only ~5,000 ft of altitude.

Something was very wrong with this airplane. I just continue to try and keep the families of the victims in my thoughts.

Trin


Exactly. In the AF447 case the pilots could have done absolutely nothing, keept their hands off of the sidestick and the aircraft would have continued flying flawlessly and stable. The pitot static would have opened up again, as it in fact did, and everything would have been ok.

But in this case the aircraft itself seems to have been hell bent on plunging straight to the ground from a low altitude, repeatedly. The crew on the previous flight did a great job saving the plane and all on board, the last crew not so lucky or skilfull.

It will be very interesting learning more facts about exactly what was going on in the plane and why. I think there is still a lot of unanswered questions.


The aircraft wasn't hell bent on plunging into the ground. It was doing exactly what it was designed to do and has been designed to do for decades. Read the Lehman article. This is likely a case of crew failing to react correctly. This hyperbole on here is getting out if hand. I would be willing to bet a VERY large sum of money that this behavior of systems has saved far more lives than it has cost.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)

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