buzzard302
Posts: 156
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 2:25 pm

zeke wrote:

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure. The pilots have to trust maintenance resolved the problem. The passengers have to trust the pilots can fly the plane...
 
ikramerica
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 2:37 pm

buzzard302 wrote:
zeke wrote:

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure. The pilots have to trust maintenance resolved the problem. The passengers have to trust the pilots can fly the plane...

The authorities have to trust the airline is providing accurate logs.

If Lion was so confident, would they need to have a mechanic fly along?
Of all the things to worry about... the Wookie has no pants.
 
buzzard302
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 2:42 pm

ikramerica wrote:
buzzard302 wrote:
zeke wrote:

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure. The pilots have to trust maintenance resolved the problem. The passengers have to trust the pilots can fly the plane...

The authorities have to trust the airline is providing accurate logs.

If Lion was so confident, would they need to have a mechanic fly along?


I agree. If Lion was not confident in the repair, they should not have flown the airplane that day. I originally commented that the pilots made a bad decision to go ahead with the flight. I pull back on that opinion, as the pilots basically trust they are taking a serviceable plane. This crash started with red flags days ahead of the actual occurrence.
 
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PixelFlight
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 3:10 pm

zeke wrote:
If an AOA is deemed faulty ideally in my view MCAS/STS/Mach trim should all be taken offline and pilots made aware they have reduced protections and need to manually trim with the trim switches. Keep in mind your watch might have more processing power than the FCC, its just a 16 bit computer.

Kalman filters was running well even on computers as old as those on the Apollo missions.
Processing power is not the issue here. The issue to not use the proper algorithm for a safety critical component.
 
trent768
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 3:22 pm

ikramerica wrote:
buzzard302 wrote:
zeke wrote:

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure. The pilots have to trust maintenance resolved the problem. The passengers have to trust the pilots can fly the plane...

The authorities have to trust the airline is providing accurate logs.

If Lion was so confident, would they need to have a mechanic fly along?

Maybe so that the mechanic know what's wrong with the aircraft? It was said that this is a recurring problem even after the appropriate measure was taken.
 
patplan
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 3:50 pm

MSPNWA wrote:
zeke wrote:
Finding fault with the mechanics involved or the airlines is very expeditious and easy, but I find it to be groundless at this stage.


What isn't groundless at this stage is that this airplane had no business being in the air hauling passengers without thorough tests to confirm proper function. That's on Lion Air as a whole.

EChid wrote:
You're aware that LionAir isn't the one conducting the search, right? It's not like they are out in diving suits yelling "Nope, nothing to see here" at the authorities while they secret the CVR away.


They are valid suspicions. The lack of a CVR is extremely suspicious at this point. Your claim is also conjecture and isn't any more valid.


Do consider these things first:
1. The aircraft hit a shallow water [of around 100 feet deep] with the impact speed of about 400+ knts [that's about 460+MPH or 750+KPH or 0.61+ Mach at sea level]
2. Almost NONE of the aircraft parts remained intact, saved for the lucky tires, scrunched engine and parts of fuselage still sits at the bottom.
3. The FDR "blackbox" found with its casing badly damaged, and the CVR when found would fare the same way or perhaps worse. There was some indications that the CVR had suffered a more significant damage due to the impact that its pinger degraded so quickly due to leakage.
3. NONE of the victims' bodies resembled a complete human corpse, save some torsos, body parts here and there.
4. ONLY 125 victims out of 187 could be identified through their DNA. The CAPT was "found" but not the FO.
5. Any parts of the aircraft sunk to the bottom would've also been buried beneath 3-4 feet of mud, and there will be more layer of mud as time passes.
6. There are myriads of oil and gas pipelines and submarine telecommunication cable system near the crash site.
7. Some parts of this tropical sea are notorious for its choppy water and strong undercurrent.
8. There are hundred of divers/rescuers and tons of equipment being dispatched for the effort.
9. One diver had perished, and many of divers also suffered some forms of the decompression sickness that the Indonesian authorities urged them to undergo the hyperbaric chamber therapy at their facility without charge.
10. The search is still continuing at this time, and the radius for search was about 1 KM employing all sorts of technology available.
11. Although there is currently no plan to stop the CVR search, but, eventually, it will come down to the cost. Will Lion Air [or other parties] be willing to foot the rest of the bill?

Let me put it this way: The CVR will be found eventually. The search radius is compact enough. The water is shallow enough that no super-specialized deep water submersible is needed to accomplish the task. My words are: Be patient people!!
 
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SEPilot
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 6:34 pm

One of the perils of modern technology is that it can fail in completely unexpected ways. From what I have read so far it seems that Boeing figured that the MCAS system would basically be an invisible fix to a fairly minor problem; the fact that the MAX engines provided more lift at high angle of attack than the NG and thus had less inherent stability in that situation. The only problem with this thinking is that it is fine as long as the MCAS works properly, but does not address the problem of what happens when it runs amok, as apparently happened here. So the fact that Boeing failed to explain it in their manuals and difference training. But it also appears that Lion’s pilots and maintenance technicians also failed; so it seems there will be plenty of blame to go around.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
marcelh
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 6:46 pm

SEPilot wrote:
But it also appears that Lion’s pilots and maintenance technicians also failed; so it seems there will be plenty of blame to go around.

Would they have “failed” when they were aware of the existence of MCAS?
 
MSPNWA
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 7:15 pm

zeke wrote:
I disagree. If I was presented with that Aircraft Maintenance Log I would have happily taken the jet flying.

The procedure followed were industry standard. The defect is written up, and the aircraft is worked on in accordance with the OEMs procedures and released for flight.

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


You're making an error of only looking at it from a pilot's perspective. This went well beyond the pilots. Clearly this aircraft had serious issues on the previous flight. It was the job of someone - anyone - at Lion Air to ensure the safety of that aircraft before passenger flight. They completely failed and sent up an airplane that still wasn't operating properly. Even if Lion Air is being completely trustworthy with their maintenance/repair procedures, there's a difference between operating aircraft "by the book" and operating them safety. You should know that more than anyone.
 
KingOrGod
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 7:46 pm

MSPNWA wrote:
zeke wrote:
I disagree. If I was presented with that Aircraft Maintenance Log I would have happily taken the jet flying.

The procedure followed were industry standard. The defect is written up, and the aircraft is worked on in accordance with the OEMs procedures and released for flight.

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


You're making an error of only looking at it from a pilot's perspective. This went well beyond the pilots. Clearly this aircraft had serious issues on the previous flight. It was the job of someone - anyone - at Lion Air to ensure the safety of that aircraft before passenger flight. They completely failed and sent up an airplane that still wasn't operating properly. Even if Lion Air is being completely trustworthy with their maintenance/repair procedures, there's a difference between operating aircraft "by the book" and operating them safety. You should know that more than anyone.


And what if the maintenance and trouble shooting was done "by the book" in co-operation with Boeing and their methods, and was deemed as airworthy afterwards? Where does that leave this?
 
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SEPilot
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 8:20 pm

marcelh wrote:
SEPilot wrote:
But it also appears that Lion’s pilots and maintenance technicians also failed; so it seems there will be plenty of blame to go around.

Would they have “failed” when they were aware of the existence of MCAS?

It seems highly likely that had the pilots been aware of it and how to disable it they would not have crashed. I don’t know if it was relevant to the technicians. Whatever they did, whether they did it by the book or not, it didn’t fix the problem. But I do think that this was not an “unsurvivable” event for the pilots; even though they did not understand what was happening I would think they could figure out that they were getting uncommanded trim inputs, and they should have had the wit to shut off the electric trim; that should have been within their existing knowledge even without being aware of MCAS. It was not like the AA DC-10 in Chicago where when the engine departed the leading edge slats retracted and the pilots had no way of knowing it. In that case they put a bunch of DC-10 pilots in the simulator and gave them that exact situation, and they all crashed. They took another bunch and gave them the same situation, only added the information that they had asymmetrical slats, and they all landed safely. In this situation the pilots surely knew they were getting uncommanded trim; why didn’t they do something to stop it? They did for a while, and then it appears they just gave up.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
MrBretz
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 8:23 pm

PixelFlight wrote:
zeke wrote:
If an AOA is deemed faulty ideally in my view MCAS/STS/Mach trim should all be taken offline and pilots made aware they have reduced protections and need to manually trim with the trim switches. Keep in mind your watch might have more processing power than the FCC, its just a 16 bit computer.

Kalman filters was running well even on computers as old as those on the Apollo missions.
Processing power is not the issue here. The issue to not use the proper algorithm for a safety critical component.


Some years ago I was a programmer for a Kalman filter in the navigation system of a military aircraft with an INS. So I have some understanding of Kalman filtering. But it is not magic. If your model believes certain external measurements, it incorporates them almost completely. So it is very unclear to me how a Kalman filter would have saved the situation here. It feels like possibly a couple sensors are giving bad data and no software is going to fix something like that. That’s why we have human pilots. I await the report on what happened and what the fix is.
 
markno
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 8:55 pm

I wonder if the stickshaker could make your arms tired so much that you cannot use your hands anymore.
 
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par13del
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 9:36 pm

A lot of post to re-read, but did the pilots from the previous flight write up all the problems they encountered in sync with the data from the flight recorder?
We have talk of maintenance following procedures, did they have all the problems listed?
 
fadecfault
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 10:30 pm

zeke wrote:
fadecfault wrote:
Sorry but the autopilot function of stab trim was not controllable.


MCAS, STS, and Mach trim are completely automatic features, pilots never control these.

fadecfault wrote:
Just because you can trim the other way does not make it controllable.


Yes it does, because the pilot can move the trim to position they desire. Fact that you need more or less trim at a later time does not make it uncontrollable. The FDR shows they were able to control the STAB most of the time. I just don’t know what happened just before the terminal dive.

fadecfault wrote:
The AOA was a problem. Why? The AOA has Dual Synchros, one synchro for the Smyd and the other for Adiru. The Symd operates the onside stick shaker and the Adiru feeds the FCCs for mcas. Both were feed erroneous information.


The SYMD also has ADIRU 1+2 inputs.

fadecfault wrote:
I did a function test of mcas last night on a MAX aircraft. Yes Stab trim went to zero while pulling back on the control column, However it was stopped and reversed at the same speed using the electric trim switches. I believe it took about 7-8 seconds to go from 4 units to 0.


The book says 0.27 units per second, should have taken twice as long. No reason MCAS should ever go to zero, that is just a poor design choice.

fadecfault wrote:
Yes the trim switches are relabeled PRI and B/U. They are redundant now it it does not matter which switch you hit.


However the MCAS function was left out of FCOM.


The Smyd receives input from the adirus for airspeed information, not AOA. I can not find anything that says the adiru sends AOA data to the smyd nor would it make sense.

I found this Interesting piece of information in my NG training manual

SWS - GENERAL DESCRIPTION
General
The stall warning system shakes the control column when the
airplane gets close to a stall.
On later effectivity aircraft, the stall ID system makes sure the pilot
cannot easily overcome automatic nose down trim of the airplane
during a stall.

During a stall, the stall warning system increases
control column feel forces.
These are the components of the stall warning system:
- Stall management yaw dampers (SMYDs)
- Control column shakers
- Stall warning test panel
- Elevator feel shift module (EFSM) - if installed
These are the components and systems that supply data to the
stall warning system:
- Stall warning test panel
- Angle of attack sensors
- Air data inertial reference system (ADIRS)
- Flap position transmitters
- Flap slat electronics unit (FSEU)
- Common display system (CDS)
- Mode control panel (MCP)
- Proximity switch electronic unit (PSEU)
The control column shakers receive a discrete signal from the stall
warning system.
Aircraft with Elevator Feel Shift Module
During a stall, the FCCs command the stabilizer to trim the
airplane nose down. The EFSM and column cut-out switch
modules operate to make sure the pilot cannot easily stop this
automatic stabilizer movement with the elevator control column
nose up input.


Sound Familiar? this is for the NG, not MAX. This has a duplication date of 11/2016.
The views and opinions written here are my own and do not reflect those of my employer.
 
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PixelFlight
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Sun Nov 25, 2018 11:24 pm

MrBretz wrote:
Some years ago I was a programmer for a Kalman filter in the navigation system of a military aircraft with an INS. So I have some understanding of Kalman filtering. But it is not magic. If your model believes certain external measurements, it incorporates them almost completely. So it is very unclear to me how a Kalman filter would have saved the situation here. It feels like possibly a couple sensors are giving bad data and no software is going to fix something like that. That’s why we have human pilots. I await the report on what happened and what the fix is.

I just mentioned it because it first run on primitive computer. But it's one of the simplest member of the predictive filter family, and you are correct: it's not the best fit for the task. There exists papers about simple predictive filers tested for aircraft sensors redundancy and the usual conclusion are that a more complex flight dynamic model is require into the predictor.

My point of view is that today technology is perfectly able to integrate a fairly accurate flight dynamic model feed by a lot of sensors, so that the failure of a few of them will not disturb the output histogram of probability. A good flight dynamic predictor would have automatically assigned a low probability to the failed AoA sensor because the vertical and horizontal acceleration data and the pitch angle data from the multiple inertial reference units and the positions delta from the GPS would really don't match what there would be in case this failed AoA sensors was right, in addition to the fact that the other AoA sensor would have coherently and perfectly match the prediction.
 
fadecfault
Posts: 164
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 12:47 am

markno wrote:
I wonder if the stickshaker could make your arms tired so much that you cannot use your hands anymore.

Only the captain's sticker shaker was operating. The stick shakers are independent in operation and rely on their onside aoa/smyd to operate.
The views and opinions written here are my own and do not reflect those of my employer.
 
EChid
Posts: 546
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 1:48 am

KingOrGod wrote:
MSPNWA wrote:
zeke wrote:
I disagree. If I was presented with that Aircraft Maintenance Log I would have happily taken the jet flying.

The procedure followed were industry standard. The defect is written up, and the aircraft is worked on in accordance with the OEMs procedures and released for flight.

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


You're making an error of only looking at it from a pilot's perspective. This went well beyond the pilots. Clearly this aircraft had serious issues on the previous flight. It was the job of someone - anyone - at Lion Air to ensure the safety of that aircraft before passenger flight. They completely failed and sent up an airplane that still wasn't operating properly. Even if Lion Air is being completely trustworthy with their maintenance/repair procedures, there's a difference between operating aircraft "by the book" and operating them safety. You should know that more than anyone.


And what if the maintenance and trouble shooting was done "by the book" in co-operation with Boeing and their methods, and was deemed as airworthy afterwards? Where does that leave this?

There is no point in trying to debate with MSPNWA on this. This is the person who's suggesting that nefarious LionAir employees, not the Indonesian authorities, are somehow overseeing the investigation and suppressing the CVR, when there is absolutely zero evidence to point to that.

At some point, this thread splits into two camps. Those who wish to dig in the interaction of human and technology to discuss the source of the issue, which is a very complex subject that takes many months (or years) to resolve, and those who wish to oversimplify the cause so as resolve the questions within their minds as quickly as possible. Sometimes that can turn into a slippery slope of conspiracy theories as we saw with MH370.
2018: DRW-PER-HKG-ICN-MEL-AVV-BNE-OOL-SYD-YYZ-YYZ-YUL-YVR-PDX-SEA-SFO-PEK-KIX-CDG-IST-NRT-HND-BKK-FAT; AC J-TK J-OZ F-DL F-TG J/F-NH J/F-CX J-VA J
 
KiloAlfaTango
Posts: 2
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:43 am

For experts. how behaved an Airbus 320 in this similar conditions. Sorry for my bad English.
 
mandala499
Posts: 6589
Joined: Wed Aug 29, 2001 8:47 pm

Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:43 am

zeke wrote:
However on the MAX they have renamed these switches, the Stab Trim MAIN ELEC and AUTO PILOT are now named PRI and B/U. Just adding more confusion to the situation.

And only a 1 hour Difference Course on the iPad on some airlines. Have we taken "commonality too far" ?

zeke wrote:
Looking at the heading information and what I have previously done with the ADS-B data I saw a left turn commenced, maybe the crew commenced a left turn to return to CGK and simply ran out of elevator to keep the aircraft level in the turn.

That change in thrust lever and the turn... may explain the different force inputs sensed by the left and right yokes?

ikramerica wrote:
Shouldn’t a Max type rated pilot know the new names and what they do?

And the hours they spent in the NG to MAX difference course is how long? Let's see...

https://www.seattletimes.com/business/b ... air-crash/



APA spokesman Dennis Tajer said Monday that the detail on the MCAS system “is new infor_mation for us.”



He said his training on moving from the old 737 NG model cockpit to the new 737 MAX consisted of little more than a one-hour session on an iPad. The airline doesn’t have simulators specific to the MAX model.


zeke wrote:
I think we are are dealing with an intermittent partial ADIRU fault.

This has been my suspicion since day one.

zeke wrote:
I would be very surprised if Boeing was not aware of this issue as well prior to the flight, the aircraft dumps a lot of data, and I think the airline would have run this issue by the OEM technical representative attached to the airline for suggestions. Everyone is learning with new aircraft.

And it happened on a weekend. The tech rep would be having his/her days off...

zeke wrote:
If an AOA is deemed faulty ideally in my view MCAS/STS/Mach trim should all be taken offline and pilots made aware they have reduced protections and need to manually trim with the trim switches.

Zeke, you gotta find a different way to word that sentence, it sounds so Airbus... the hardcore Boeing fanboys are going to have a hard time accepting that. J/K :)

Jokes aside, yes, something along those lines would be a nice start on fixing this problem.

bizzard302 wrote:
And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure.

With hindsight, we all know NOW that the aircraft shouldn't have flown. The question now is, what prevented them from being able to diagnose the problem correctly?

bizzard302 wrote:
This crash started with red flags days ahead of the actual occurrence.

Make that "over the weekend"... I am told the that the aircraft was more or less perfect until that weekend... but then I have no way to verify that claim.

Oh the Onboard Mechanic issue that keeps getting questioned from time to time:
ikramerica wrote:
Outstation Mechanic with years of experience on the NG but probably very little on the Max onboard to monitor problematic aircraft.

ikramerica wrote:
If Lion was so confident, would they need to have a mechanic fly along?

trent768 wrote:
Maybe so that the mechanic know what's wrong with the aircraft?

In Indonesia, an onboard mechanic/engineer is nothing related to an aircraft having problems from the previous flight. They're there to release the aircraft should the aircraft develop a problem that can be deferred, should that problem occur at an outstation. Placing engineers at outstations can be more expensive than the loss of revenue from 1 seat plus flight pay, because aviation in Indonesia is very Jakarta-centric. Place someone at an outstation and the company has to fork out money for his accomodation and outstation pay, plus transportation to go back and forth to Jakarta or nearest maintenance base, and get a back up person. And you can't just get any engineer certified/rated on the type at an outstation to do stuff for you, the guy has to be approved on the type AND approved by the DGCA to do work for your airline. Now, Outstation based 3rd party contractors can be very expensive because of that. The same happens with dispatchers, and loadsheeters, it's not uncommon in Indonesia to see an engineer and a dispatcher onboard to outstations. Moves by the industry to make the use of certified 3rd party contractors and to make such a thing cheaper was effectively blocked by the previous transport minister in the aftermath of the Air Asia crash in end of 2014, because he seems to believe that safety should be expensive. Heck, he banned the use of centralized dispatch and tried to ban the use of approved weather information in computerized flight plans and dispatch briefs "because they're not from the national weather bureau", despite the national weather bureau were giving out the same exact information and source as those within the airline dispatch briefs!

patplan wrote:
Do consider these things first:

Oh the conspiracy theorists won't let that get in their way...

EChid wrote:
At some point, this thread splits into two camps. Those who wish to dig in the interaction of human and technology to discuss the source of the issue, which is a very complex subject that takes many months (or years) to resolve, and those who wish to oversimplify the cause so as resolve the questions within their minds as quickly as possible. Sometimes that can turn into a slippery slope of conspiracy theories as we saw with MH370.

Attepts to make it go down that slippery slope of conspiracy theories (including ones alleging that some member(s) of a.net is part of a coverup conspiracy) has been attempted... unfortunately... but at least the majority doesn't want to play along with that game.

The camps formed at the moment:
1. The It's only Lion's fault camp
2. The It's only Boeing's fault camp
3. The Let's just get to the bottom of the problem camp

The #3 camp goes something along the lines of the following:
kalvado wrote:
This is not about loyalty to A, B, AA, ALPA, XYZ, ETC - this is about preventing future accidents.

Something that I agree with.
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:54 am

fadecfault wrote:
I can not find anything that says the adiru sends AOA data to the smyd nor would it make sense.


The SYMD receives ADR data from the ADIRU, what it does with the data low level I do not know. That data does include the airspeed, altitude, TAT, AOA.

Image
Image

As you can see the SYMD however does not move the stabilizer or elevator

Image
Image

The SYMD activates the feel shift

Image


fadecfault wrote:
During a stall, the FCCs command the stabilizer to trim the
airplane nose down. The EFSM and column cut-out switch
modules operate to make sure the pilot cannot easily stop this
automatic stabilizer movement with the elevator control column
nose up input.

Sound Familiar? this is for the NG, not MAX. This has a duplication date of 11/2016.


No, that is referring to the STS stall function

Image

The FDR data shows the stick shakier coming on immediately after liftoff, however the nose down trim inputs did not start then. The STS command can be seen in the initial climb, the MCAS commands can be seen when clean. The MCAS trim commands were interrupted 5 seconds after each time the pilot made a trim control. The paragraph also clearly states it is the FCC commanding nose down, which is what we have been saying all along, these are the automatic trim functions in the FCC that the pilots have no control over, Mach, STS, and MCAS.

Also if this was generated by the SYMD, we should have seen the SMYD autoslat system commanding automatic slats extension.

I still do not know what was going on at the label 26 I identified before. this may have been a situation where it changed from MCAS diving the trim to STS driving the trim.
Last edited by zeke on Mon Nov 26, 2018 3:01 am, edited 1 time in total.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:57 am

buzzard302 wrote:
We now all know the aircraft was not actually in serviceable condition.


Only with the benefit of hindsight, the aircraft was released in a fully serviceable condition.

buzzard302 wrote:
So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault.


The will form part of the investigation.

ikramerica wrote:
The authorities have to trust the airline is providing accurate logs.


There is no reason to suggest they have not. The log is not just a single piece of paper, it normally has 3-4 "carbon" copies of each page, each copy has a different use. Forensic analysis on the copies is easy to determine if alternations we made.

ikramerica wrote:
If Lion was so confident, would they need to have a mechanic fly along?


I would not read too much into that. We have mechanics onboard for some time after we received the A350, many of the out ports did not have mechanics trained on the new aircraft, and the new aircraft produced so much data we needed mechanics to download the post flight data onto a USB stick. Now we dont need to do that as everyone has been trained, and we have 3G/4G data links at every outport to download the aircraft data onto.

PixelFlight wrote:
The issue to not use the proper algorithm for a safety critical component.


I have already adequately covered my view that they should not be using a single sensor single processor design.

MSPNWA wrote:
Clearly this aircraft had serious issues on the previous flight. It was the job of someone - anyone - at Lion Air to ensure the safety of that aircraft before passenger flight. They completely failed and sent up an airplane that still wasn't operating properly. Even if Lion Air is being completely trustworthy with their maintenance/repair procedures, there's a difference between operating aircraft "by the book" and operating them safety. You should know that more than anyone.


This is all being said with the benefit of hindsight, the procedures the airline were following in terms of reporting and fixing the issue are industry standard. If we were to replace an engine after it failed, we follow the AMM and perform ground tests called for under the AMM and release the aircraft for flight as being serviceable. No special test flight is required, and I would not hesitate flying the aircraft. There is the public perceptions, and what really happens day to day in industry which are poles apart.

Pilots and mechanics are not risk takers, we want to get back to our families as much as anyone else after a days work. If anything we are more cautious than the general public who think the items in pre-flight safety briefings apply to everyone else except them.

markno wrote:
I wonder if the stickshaker could make your arms tired so much that you cannot use your hands anymore.


Stick shaker is more of a noise maker and an annoyance, it basically just vibrates the control column.
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 3:27 am

EChid wrote:
There is no point in trying to debate with MSPNWA on this. This is the person who's suggesting that nefarious LionAir employees, not the Indonesian authorities, are somehow overseeing the investigation and suppressing the CVR, when there is absolutely zero evidence to point to that.

At some point, this thread splits into two camps. Those who wish to dig in the interaction of human and technology to discuss the source of the issue, which is a very complex subject that takes many months (or years) to resolve, and those who wish to oversimplify the cause so as resolve the questions within their minds as quickly as possible. Sometimes that can turn into a slippery slope of conspiracy theories as we saw with MH370.


I'll take the reason for that is because I will talk about inconvenient facts and and want to get to the bottom of it no matter who is involved.

zeke wrote:
This is all being said with the benefit of hindsight, the procedures the airline were following in terms of reporting and fixing the issue are industry standard. If we were to replace an engine after it failed, we follow the AMM and perform ground tests called for under the AMM and release the aircraft for flight as being serviceable. No special test flight is required, and I would not hesitate flying the aircraft. There is the public perceptions, and what really happens day to day in industry which are poles apart.


This was not as simple as a routine engine change, and you know it. Stop making excuses for parties (except one) that may have contributed to this horrible crash. We have a plane that was clearly not airworthy on its final flight, and there were repeated episodes of it with this airframe. I hope you're not implying that it's okay for an airline to treat life like a video game where "taking another shot" at fixing a serious persistent problem is enough to fly customers as usual (assuming that checked off "by the book").
 
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 4:02 am

MSPNWA wrote:
This was not as simple as a routine engine change, and you know it. Stop making excuses for parties (except one) that may have contributed to this horrible crash.


I am not making excuses, nor am I dramatising the facts. Everything they did from what I can see was industry standard.

“routine engines change” :banghead:

MSPNWA wrote:
We have a plane that was clearly not airworthy on its final flight, and there were repeated episodes of it with this airframe.


For an aircraft to be airworthy it needs

Certificate of Registration
Certificate of Airworthiness
Radio station licence
Certificate of maintenance review
To have been released for flight

Please tell me what document JT610 did I not have to base your claim on ?
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
EChid
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 4:08 am

MSPNWA wrote:
I'll take the reason for that is because I will talk about inconvenient facts and and want to get to the bottom of it no matter who is involved.

Yeah, spoken like a conspiracy theorist. "I'm willing to speak the truth when no one else is."

Look, I don't think anyone on these forums with *any* knowledge of aviation disasters is claiming that LionAir is in the free and clear, because that's usually not how modern aviation crashes work. It's usually that various things came together to create the unfortunate incident, just as those things *didn't* come together for AC, AA, WN, or any of the other major operators.

The reasons that this thread has reached so many pages is not because we don't believe LionAir played a role in this, but because major crashes that may be the partial result of a design flaw are quite rare and points to a systemic failure that affects far more than one airline. That's big news, especially from a company as well established as Boeing, whereas the failure of one crew, or one maintenance event, is comparatively less significant (although still concerning to the company, its passengers, and its regulatory body).

You're mistaking the focus of the discussion for a complete view of the cause.
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patplan
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 4:38 am

MSPNWA wrote:
...
zeke wrote:
This is all being said with the benefit of hindsight, the procedures the airline were following in terms of reporting and fixing the issue are industry standard. If we were to replace an engine after it failed, we follow the AMM and perform ground tests called for under the AMM and release the aircraft for flight as being serviceable. No special test flight is required, and I would not hesitate flying the aircraft. There is the public perceptions, and what really happens day to day in industry which are poles apart.


This was not as simple as a routine engine change, and you know it. Stop making excuses for parties (except one) that may have contributed to this horrible crash. We have a plane that was clearly not airworthy on its final flight, and there were repeated episodes of it with this airframe. I hope you're not implying that it's okay for an airline to treat life like a video game where "taking another shot" at fixing a serious persistent problem is enough to fly customers as usual (assuming that checked off "by the book").


"As simple as a routine engine change"?? I'm intrigued...

Do you mean "flushing the pitot tube" and/or "replacing AOA sensor" of an aircraft were not as simple as an aircraft's "routine engine change" ?? Or, do you mean an aircraft's engine change is more simple and routine than, say..., "flushing the pitot tube" and "replacing the AOA sensor"?? Or was it "engine change" was a simple process and routinely done to an aircraft??

Please elaborate..., like I said..., I am intrigued...[perhaps others who follow your posts are as well...]
 
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Starlionblue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 4:56 am

KiloAlfaTango wrote:
For experts. how behaved an Airbus 320 in this similar conditions. Sorry for my bad English.


IMHO, an A320 would never have gotten into this situation because there wouldn't be a single sensor input path leading to a "disguised" automated flight control input.

With the caveat that I might not quite understand MCAS, the intermittent nature of MCAS might be rather confusing to the pilots. The problem isn't necessarily "fixed" once MCAS stops making an input. Either your AoA is too high or it isn't. In an Airbus, if alpha is too high, this triggers Alpha Prot. And you don't get out of Alpha Prot until the AoA is back in a safe range.

From a high-level perspective, the Airbus A320 was designed from the ground up for fly-by-wire, computerised control. There have been some changes to the systems (such as Backup Speed Scale) but fundamentally the control systems on a A320 built in 1988 are the same as one built in 2018. By contrast, the 737 was designed for mechanical control, with more and more electronic features added through the design generations (Original, Classic, NG and MAX) as more efficiency was required, weight increased and thrust increased.
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1989worstyear
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 5:01 am

PixelFlight wrote:
MrBretz wrote:
Some years ago I was a programmer for a Kalman filter in the navigation system of a military aircraft with an INS. So I have some understanding of Kalman filtering. But it is not magic. If your model believes certain external measurements, it incorporates them almost completely. So it is very unclear to me how a Kalman filter would have saved the situation here. It feels like possibly a couple sensors are giving bad data and no software is going to fix something like that. That’s why we have human pilots. I await the report on what happened and what the fix is.

I just mentioned it because it first run on primitive computer. But it's one of the simplest member of the predictive filter family, and you are correct: it's not the best fit for the task. There exists papers about simple predictive filers tested for aircraft sensors redundancy and the usual conclusion are that a more complex flight dynamic model is require into the predictor.

My point of view is that today technology is perfectly able to integrate a fairly accurate flight dynamic model feed by a lot of sensors, so that the failure of a few of them will not disturb the output histogram of probability. A good flight dynamic predictor would have automatically assigned a low probability to the failed AoA sensor because the vertical and horizontal acceleration data and the pitch angle data from the multiple inertial reference units and the positions delta from the GPS would really don't match what there would be in case this failed AoA sensors was right, in addition to the fact that the other AoA sensor would have coherently and perfectly match the prediction.


Sadly - we probably won't see this for another 30 years for NB's, as there won't be any clean sheet designs until then.
Stuck at age 15 thanks to the certification date of the A320-200 and my parents' decision to postpone having a kid by 3 years. At least there's Dignitas...
 
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 6:38 am

Starlionblue wrote:

IMHO, an A320 would never have gotten into this situation because there wouldn't be a single sensor input path leading to a "disguised" automated flight control input.


That is not true, there has been a spate of them on 737/757, A319/20/21/30/40 which lead to the FAA AD 2000-07-27. Qantas operated VH-QPA it had an ADIRU 1 issue in 2006 which had numerous NAV IR1 FAULT and NAV ADR 1 FAULT, the same aircraft two years later the same aircraft had two uncommanded pitch down events, again the source was ADIRU 1. The flight control computers in normal law are programmed to believe a stall warning whenever generated, it is up to the pilots if they think the data is invalid to follow the procedure to turn off the ADR to get out of normal law back to direct law. They have the warning that they have lost their protections.

Even steam driven Airbuses aircraft are susceptible, for example KQ 431 an A310 which crashed after takeoff as one of the AOA vanes was damaged by group support equipment and the aircraft received stall warnings and stick shaker immediately after liftoff.
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Starlionblue
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 8:40 am

zeke wrote:
Starlionblue wrote:

IMHO, an A320 would never have gotten into this situation because there wouldn't be a single sensor input path leading to a "disguised" automated flight control input.


That is not true, there has been a spate of them on 737/757, A319/20/21/30/40 which lead to the FAA AD 2000-07-27. Qantas operated VH-QPA it had an ADIRU 1 issue in 2006 which had numerous NAV IR1 FAULT and NAV ADR 1 FAULT, the same aircraft two years later the same aircraft had two uncommanded pitch down events, again the source was ADIRU 1. The flight control computers in normal law are programmed to believe a stall warning whenever generated, it is up to the pilots if they think the data is invalid to follow the procedure to turn off the ADR to get out of normal law back to direct law. They have the warning that they have lost their protections.

Even steam driven Airbuses aircraft are susceptible, for example KQ 431 an A310 which crashed after takeoff as one of the AOA vanes was damaged by group support equipment and the aircraft received stall warnings and stick shaker immediately after liftoff.


I stand corrected.
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ferpe
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 10:41 am

aaexecplat wrote:
Seems like the pilots had a good handle on the trim to that point...why did they stop countering the MCAS at 22-ish to the same extent they had previously? Distracted by a new/different problem?


That question is the very key and I think the answer will come from the CVR.

They were doing a very good job in the circumstances with the stick shaker on continuously and countering MCAS to keep the aircraft level around 5000 ft and around 250 kts. Despite what was going on they were still in control and flying.

Looking at the heading information and what I have previously done with the ADS-B data I saw a left turn commenced, maybe the crew commenced a left turn to return to CGK and simply ran out of elevator to keep the aircraft level in the turn.

Thrust is increased at this time suggesting that at least one hand had to be removed from the control column.

AirlineCritic wrote:
Why did the pilots not use the cut out switch for the MCAS? Did not know/understand? Other reason?
.


Which switch ?

This is the description for the 737NG, what the pilots would be most familiar flying, the correct switch is the autopilot cutout switch to turn off MCAS even when flying manually.


Zeke, I've read all your posts and I agree with your analysis which is really professional. Where I can perhaps add something:

1. I'm not sure Boeing has MCAS operating through the Autopilot Cutout path. It's an anti-stall function, operating at the region just before stall. I don't think you can get FAA certification of the function if it's inhibited when a crew has thrown the Autopilot Cutout switch for some reason. Same with the Manual trim path. I've been very intrigued by Boeing's bulletin saying you should Cut out both circuits, this has made me suspicios MCAS is wired to work both paths for the reasons I just gave. And Boeing having renamed the Switches to something I can't quite understand, it makes me think dual path MCAS authority even more.

2. Why did the crew stop trimming to fully compensate MCAS between 22 and 26 in your annotated FDR graph? This is the mystery. I think we must think about how the crew sensed the MCAS and STS work from a rouge AOA value (I've been suspecting a downstream fault ever since learning they changed the sensor). You only sense it through a nose down pitch (sensed through G and nose position), which they then counter with nose up trim until they sensed a balanced trim position. Your ADS-B track and the stick force graph indicate a turn starting at 22. In a turn, it's much harder to sense what is happening in pitch. You have an STS which has increased stick forces before you go into the turn, it means you conduct the turn with even higher stick pull force than normal, to the point where both might have to pull on the yoke. This makes it harder to feel any background MCAS/STS as the pilots can't be sure if it's because the other is pulling less or more or the aircraft which is pulling/changing how much evelvator is needed.

We see there are several short trim-up inputs but they don't compensate a MCAS stabilizer nose down. And how should they know. They are not sure if they reached a trimmed position as they are in a turn with stiff arms pulling hard (no trimmed position sensation in the arms) and the turn renders a pitch movement check of trim not possible. Let's wait with the trimming until we are leveling out of the turn, pilots are trained to not trim out a stick force in a turn. The stabilizer continues the nose down until the elevator gets flow breakdown (elevator stall) and the nose pitches so violently down they get thrown up and might hurt themselves against the overhead panel which is close on a 737. I haven't experienced an elevator stall but several G induced wing flip stalls through 180° on fighters. It happens in a fraction of a second and it's so violent you bang your head on the canopy. They keep max elevator on during the violent nose down as this is logical if you get pulled off your seat, you hold on to what you have in your hands. And this is why the elevator stall remains and no correction of the dive is effective before hitting the water.

BTW, I agree, it's not a stabilizer trim runaway as sensed and analyzed by the crew. The previous crew was lucky they hit both Cutout switches, a more analyzing crew might not do it for the reasons you give.
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StTim
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 11:02 am

Thanks ferpe - great thoughts and why I read this forum - to learn.
 
Flyglobal
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 11:32 am

Sounds like a very good analysis (for a non Pilot). Awaiting zeke's comments.

Flyglobal
 
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 11:44 am

mandala499 wrote:
zeke wrote:
I think we are are dealing with an intermittent partial ADIRU fault.

This has been my suspicion since day one.


Can this in some aspects be compared to the ADIRU "strange" failure on an A330 a couple of years ago?
Three in a row makes a dive:
* processing error in the ADIRU,
* intermittent false data not inhibited as by spec,
* Airbus sanitizing algo had a time constant that amplified the not to be expected erroneous data.

Who made the MAX Adiru?
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JibberJim
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 12:25 pm

I recall being told that MCAS alternated which AOA sensor it used, toggling when weight on wheels cycling. However the FDR shows MCAS doing its stuff on both the last two flights, does that mean the alternation of AOA sensor isn't something that MCAS does, or does it point to the fault being elsewhere than the AOA sensor itself (as has been suggested anyway)
 
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PixelFlight
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 12:52 pm

1989worstyear wrote:
PixelFlight wrote:
MrBretz wrote:
My point of view is that today technology is perfectly able to integrate a fairly accurate flight dynamic model feed by a lot of sensors, so that the failure of a few of them will not disturb the output histogram of probability.

Sadly - we probably won't see this for another 30 years for NB's, as there won't be any clean sheet designs until then.

We will see. I still have hope when I see transition like for the AFDX https://en.wikipedia.org/wiki/Avionics_ ... d_Ethernet
 
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flyingturtle
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 12:58 pm

JibberJim wrote:
I recall being told that MCAS alternated which AOA sensor it used, toggling when weight on wheels cycling.


Such a weird "solution"... :eyepopping:

When you have two sensors, you can use data from both sensors. Goddammit.

David
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fadecfault
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 12:59 pm

zeke wrote:
fadecfault wrote:
I can not find anything that says the adiru sends AOA data to the smyd nor would it make sense.


The SYMD receives ADR data from the ADIRU, what it does with the data low level I do not know. That data does include the airspeed, altitude, TAT, AOA.

Image
Image

As you can see the SYMD however does not move the stabilizer or elevator

Image
Image

The SYMD activates the feel shift

Image


fadecfault wrote:
During a stall, the FCCs command the stabilizer to trim the
airplane nose down. The EFSM and column cut-out switch
modules operate to make sure the pilot cannot easily stop this
automatic stabilizer movement with the elevator control column
nose up input.

Sound Familiar? this is for the NG, not MAX. This has a duplication date of 11/2016.


No, that is referring to the STS stall function

Image

The FDR data shows the stick shakier coming on immediately after liftoff, however the nose down trim inputs did not start then. The STS command can be seen in the initial climb, the MCAS commands can be seen when clean. The MCAS trim commands were interrupted 5 seconds after each time the pilot made a trim control. The paragraph also clearly states it is the FCC commanding nose down, which is what we have been saying all along, these are the automatic trim functions in the FCC that the pilots have no control over, Mach, STS, and MCAS.

Also if this was generated by the SYMD, we should have seen the SMYD autoslat system commanding automatic slats extension.

I still do not know what was going on at the label 26 I identified before. this may have been a situation where it changed from MCAS diving the trim to STS driving the trim.


No AOA adiru Data to the Symd
Image
Per the MAX SDS:
ADIRS - LEFT AIR DATA OUTPUTS
SMYD 1
The ADIRU sends this data to SMYD 1:
Mach
True airspeed
Computed airspeed
Impact pressure.

ADIRS - LEFT INERTIAL REFERENCE DIGITAL OUTPUTS
SMYD

SMYD 1 uses this IR data to calculate stall management and yaw damper values:

Pitch angle
Roll angle
Body roll rate
Body yaw rate
Body longitudinal acceleration
Body lateral acceleration
Body normal acceleration
Inertial vertical speed

Image
VS
Image

My point is the NG Nose down Stall recovery is not all that different than mcas. Some are making it out to seem as if the pilots were blindsided by a totally new system on the max when a similar system already existed on the NG.
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estorilm
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 1:03 pm

buzzard302 wrote:
zeke wrote:

As far as everyone was concerned the aircraft was fully serviceable without a single MEL applied.


And that there lies the fundamental problem. We now all know the aircraft was not actually in serviceable condition. So it raises the question whether maintenance tests/procedures are actually sufficient for this type of fault. Maintenance has to trust Boeing's repair procedure. The pilots have to trust maintenance resolved the problem. The passengers have to trust the pilots can fly the plane...

Right, but as far as the fundamentals of the system and its failure mode are concerned - isn't that kind of meaningless? That initial failure could have occurred on the accident flight, without any possibility of maintenance fixing it.
 
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drerx7
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 1:45 pm

Been following this thread in its entirety...I'd like to consider myself a very astute non biased aviation enthusiast...my question is this: Should the traveling public have reservations about flying a MAX right now? As I understand without any further info from the crash is that every one of these could have a faulty AOA or ADIRU. Is it that now flight crew are now aware on how to disable the MCAS in the event the aircraft behaves erratically?
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:03 pm

drerx7 wrote:
Been following this thread in its entirety...I'd like to consider myself a very astute non biased aviation enthusiast...my question is this: Should the traveling public have reservations about flying a MAX right now? As I understand without any further info from the crash is that every one of these could have a faulty AOA or ADIRU. Is it that now flight crew are now aware on how to disable the MCAS in the event the aircraft behaves erratically?


As vocal as a few unions have been about the flow of information and training materials, if they are not calling for a grounding then I can surmise there is an interim workaround. Nonetheless, I’d probably be a bit uncomfortable as a non-aviation professional.
-Dave


MAX’d out on MAX threads. If you are starting a thread, and it’s about the MAX - stop. There’s already a thread that covers it.
 
kalvado
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:10 pm

drerx7 wrote:
Been following this thread in its entirety...I'd like to consider myself a very astute non biased aviation enthusiast...my question is this: Should the traveling public have reservations about flying a MAX right now? As I understand without any further info from the crash is that every one of these could have a faulty AOA or ADIRU. Is it that now flight crew are now aware on how to disable the MCAS in the event the aircraft behaves erratically?

Information is out, MCAS runaway on another flight is pretty much out of question as pilots would know the drill.
a single failed electronic block is not a crash issue. It is some marginal effects in stall recovery which are questionable IMHO - but chances of encountering that are below chances of dying in car crash on the way to the airport. WHich may still be higher than where the industry is aiming, though.
 
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:17 pm

ferpe wrote:
1. I'm not sure Boeing has MCAS operating through the Autopilot Cutout path. It's an anti-stall function, operating at the region just before stall. I don't think you can get FAA certification of the function if it's inhibited when a crew has thrown the Autopilot Cutout switch for some reason. Same with the Manual trim path. I've been very intrigued by Boeing's bulletin saying you should Cut out both circuits, this has made me suspicios MCAS is wired to work both paths for the reasons I just gave. And Boeing having renamed the Switches to something I can't quite understand, it makes me think dual path MCAS authority even more.


MCAS as far as I am aware is shutoff if the FCC output is terminated. MCAS to me is a little like an extension to the STS Stall function which was not in the aircraft when the FAA certified it. That was an add on under instruction by the JAA/EASA at the time before they would certify it. This was by way of a software modification.

The emergency AD does shed some light onto the matter, http://rgl.faa.gov/Regulatory_and_Guida ... rgency.pdf
"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"

as for the manual trim path, it remains available according to the AD

"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."

ferpe wrote:
2. Why did the crew stop trimming to fully compensate MCAS between 22 and 26 in your annotated FDR graph?


I don't know.

I think this maybe human factors related, decided to return to field (hand over control to program FM ?), and sensory perception after a two minute steady climb. We can see below they lost a little altitude, the pilots response to that was to increase thrust and to commence a climb (1), thrust was reduced and it looks like they started to commence a turn to the left (2), as the turn increased, the back pressure increased, they ended up in a high speed spiral dive. Around 2500 ft it looks like the inner engine N1 stops recording, and they make an instantaneous 35-40 degree heading change.

Image

The terminal phase of JT610 reminds me of the terminal phase of the 735 crash of U9363 (this also has some good information on how STS functions), https://mak-iac.org/upload/iblock/459/r ... bn_eng.pdf

I have added a vertical line where the left turn was commenced

Image

The BEA did good sensory analysis of what the pilots would have been experiencing, you can see what the pilots perception of what the aircraft is doing following a climb and a left descending turn, the human sensors perceptions think they are still climbing.

Image

ferpe wrote:
We see there are several short trim-up inputs but they don't compensate a MCAS stabilizer nose down.


The trim inputs simply were not long enough.

ferpe wrote:
BTW, I agree, it's not a stabilizer trim runaway as sensed and analyzed by the crew. The previous crew was lucky they hit both Cutout switches, a more analyzing crew might not do it for the reasons you give.


We now know from the FAA emergency AD there was no correct procedure o follow, the AD now states

"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 "
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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PixelFlight
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:18 pm

fadecfault wrote:
zeke wrote:
fadecfault wrote:
I can not find anything that says the adiru sends AOA data to the smyd nor would it make sense.

The SYMD receives ADR data from the ADIRU, what it does with the data low level I do not know. That data does include the airspeed, altitude, TAT, AOA.

No AOA adiru Data to the Symd

Thanks fadecfault and zeke for sharing schematics.

My understanding is that a possible scenario is that the AoA sensor have 2 mechanical to analog resolver, sending one analog signal to the ADR (since it have a ADC) and a other analog signal to the SYMD. Since the AoA sensor was replaced and that the fault was still here, we suspect that the mechanical part of the sensor is not the cause of the issue. After the resolver, the two signals look separate but the numbers of symptoms, reported by the JT-43 crew and recorded by the FDR, suggest that the two signals was wrong. So what can be the common mode failure that we have not spot yet ? Maybe the power supply of the 2 mechanical to analog resolver, or is there others ideas ?
 
fadecfault
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:27 pm

drerx7 wrote:
Been following this thread in its entirety...I'd like to consider myself a very astute non biased aviation enthusiast...my question is this: Should the traveling public have reservations about flying a MAX right now? As I understand without any further info from the crash is that every one of these could have a faulty AOA or ADIRU. Is it that now flight crew are now aware on how to disable the MCAS in the event the aircraft behaves erratically?


It's not an adiru problem and the AOA is exactly the same part as the 737NG.
We regularly do functional check flights for problem aircraft and my airline would not have let this aircraft fly passengers without doing a fcf first. I have confidence any large US carrier would do the same. So no, the public should not have reservations about flying the max (or any aircraft) on an airline with a safe flying record.
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zeke
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 2:48 pm

fadecfault wrote:
No AOA adiru Data to the Symd


Thanks for the diagram, it looks like part of the system, I dont for example see the auto-slat power or commands. Do you have similar diagrams for the MCAS and STS on the MAX ?

Image[/quote]

That is VERY useful thank you, what is STM ?

I see flaps up the pilots trim is 0.2 units/sec, where MCAS is more like 0.25 (10 seconds for 2.5 units), still not sure how you managed to do 4 units in 8 seconds the other night ??

Also this information is useful. "Only the F/Os column cutout switch module is affected because it is the only module that interfaces with the FCCs".

Are you able to help me understand the change of terms being used for the cutout switches on the MAX, I thought on the NG one just turns the autopilot command off, the other power to the actual actuator. Why the change to PRI and B/U ? What is the B/U a backup to ?

fadecfault wrote:
My point is the NG Nose down Stall recovery is not all that different than mcas. Some are making it out to seem as if the pilots were blindsided by a totally new system on the max when a similar system already existed on the NG.


Well that somebody is Boeing and the FAA who issued the emergency AD, and the emergency AD basically says with erroneous AOA data MCAS may activate at much lower speeds than originally designed.
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fadecfault
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 3:13 pm

PixelFlight wrote:
fadecfault wrote:
zeke wrote:
The SYMD receives ADR data from the ADIRU, what it does with the data low level I do not know. That data does include the airspeed, altitude, TAT, AOA.

No AOA adiru Data to the Symd

Thanks fadecfault and zeke for sharing schematics.

My understanding is that a possible scenario is that the AoA sensor have 2 mechanical to analog resolver, sending one analog signal to the ADR (since it have a ADC) and a other analog signal to the SYMD. Since the AoA sensor was replaced and that the fault was still here, we suspect that the mechanical part of the sensor is not the cause of the issue. After the resolver, the two signals look separate but the numbers of symptoms, reported by the JT-43 crew and recorded by the FDR, suggest that the two signals was wrong. So what can be the common mode failure that we have not spot yet ? Maybe the power supply of the 2 mechanical to analog resolver, or is there others ideas ?


Need to know the entire timeline of maintenance events with accuracy, can't rely on news articles. It's possible a good AOA was Swapped for a Failing AOA. Unfortunately bad from stock parts do happen.
It seems the AOA was replaced right before the previous flight which had similar issues. When that flight landed maintenance in Jakarta blew out the lines and did an ops check of the pitot static system. The next day was the accident.
The views and opinions written here are my own and do not reflect those of my employer.
 
fadecfault
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 3:42 pm

zeke wrote:

That is VERY useful thank you, what is STM ?

I see flaps up the pilots trim is 0.2 units/sec, where MCAS is more like 0.25 (10 seconds for 2.5 units), still not sure how you managed to do 4 units in 8 seconds the other night ??

Also this information is useful. "Only the F/Os column cutout switch module is affected because it is the only module that interfaces with the FCCs".

Are you able to help me understand the change of terms being used for the cutout switches on the MAX, I thought on the NG one just turns the autopilot command off, the other power to the actual actuator. Why the change to PRI and B/U ? What is the B/U a backup to ?

fadecfault wrote:
My point is the NG Nose down Stall recovery is not all that different than mcas. Some are making it out to seem as if the pilots were blindsided by a totally new system on the max when a similar system already existed on the NG.


Well that somebody is Boeing and the FAA who issued the emergency AD, and the emergency AD basically says with erroneous AOA data MCAS may activate at much lower speeds than originally designed.


STM is Stab Trim Motor.
Autoslat is not covered in the differences training so I'm assuming it's the same as the NG
I'm unable to view boeing manual images at home, only text. But i don't recall the boeing manuals having detailed information for mcas only something like this:
Image
As you can see in that pic the B/U switch is just a redundant switch to the primary switch. I'm not sure of the change but because of the switch locations they can't be difficult to read which is which.
The views and opinions written here are my own and do not reflect those of my employer.
 
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AirlineCritic
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 3:53 pm

mandala499 wrote:
In Indonesia, an onboard mechanic/engineer is nothing related to an aircraft having problems from the previous flight. They're there to release the aircraft should the aircraft develop a problem that can be deferred, should that problem occur at an outstation. Placing engineers at outstations can be more expensive than the loss of revenue from 1 seat plus flight pay, because aviation in Indonesia is very Jakarta-centric. Place someone at an outstation and the company has to fork out money for his accomodation and outstation pay, plus transportation to go back and forth to Jakarta or nearest maintenance base, and get a back up person. And you can't just get any engineer certified/rated on the type at an outstation to do stuff for you, the guy has to be approved on the type AND approved by the DGCA to do work for your airline. Now, Outstation based 3rd party contractors can be very expensive because of that. The same happens with dispatchers, and loadsheeters, it's not uncommon in Indonesia to see an engineer and a dispatcher onboard to outstations. Moves by the industry to make the use of certified 3rd party contractors and to make such a thing cheaper was effectively blocked by the previous transport minister in the aftermath of the Air Asia crash in end of 2014, because he seems to believe that safety should be expensive. Heck, he banned the use of centralized dispatch and tried to ban the use of approved weather information in computerized flight plans and dispatch briefs "because they're not from the national weather bureau", despite the national weather bureau were giving out the same exact information and source as those within the airline dispatch briefs!


Thank you very much for this. Clears it up.

mandala499 wrote:
3. The Let's just get to the bottom of the problem camp


Sign me up for that, too.
 
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Re: Lion Air 737MAX8 Crashed Jakarta to Pangkal Pinang

Mon Nov 26, 2018 4:01 pm

estorilm wrote:
Right, but as far as the fundamentals of the system and its failure mode are concerned - isn't that kind of meaningless? That initial failure could have occurred on the accident flight, without any possibility of maintenance fixing it.


Indeed.

While maintenance or maintenance procedure definitions may eventually be found contributing to this accident, the bottom line is still that *something* failed in the airplane, and an accident followed. That consequence could have occurred the first time this was encountered, before maintenance would have had any chance to rectify it.

So what led to this? We don't know... exactly... yet. It could have been either multiple things going wrong, a faulty design that left the pilots without a practical option, piloting error, training/manuals error, lack of procedures for this case, or a combination of these things.

But, merely a single non-working sensor or processing unit should *not* bring an airline down, so from that perspective there is more to this story than maintenance not fixing a part. Also, for all we know they may well have performed exactly the procedures specified by Boeing, and changed all the necessary parts.

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