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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 7th Nov 2018, 12:08
  #721 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
The QF A330 that took the plunge, twice, didn't result in grounding the fleet, despite the authorities NEVER working out what happened. Airbus came up with a procedure where crews push-button-disabled a particular system.
As you probably know Capn, that OEB has now been removed with no real change in procedure but a change to the software. Airbus have now moved back to their original position whereby Airbus believe that uncommanded control inputs can’t happen and there is no procedure to counteract. It won’t take long for operational experience to move on and before long there will be a vacuum of knowledge on OEB49. The Qantas A330 got lucky that it didn’t happen close to the ground. Which reminds me, wasn’t there a 777 that had an uncommanded nose over in the same area? I have no idea of what the result of that investigation was, related?

With regards to this Lion Air flight, this is a real tragedy if it is related to this yet to be released AOA sensor bulletin. Firstly, all pilots are taught to disengage the AP when there is unreliable airspeed. So to engage an AP, which possibly could have solved the problem, is not intuitive.

Secondly, if pilots are taught in training that the aircraft will automatically command a pitch down in a stall to counteract a pilot pulling the aircraft further into the stall, it must have been confusing to have two stall indications. Along with the stall warning/stick shaker being activated there must have been a confirmation bias of a stall occurring.

Thirdly, with the state of confusion, it may not have been apparent to the pilots that the trim was stopping the nose down command. The porpoising seems to confirm that they weren’t aware of what was the cause of their issue(understandably). I wonder if when the nose dropped each time, this motion caused an illusion that the aircraft had just entered an actual stall.

Could the Air France accident had an impact on the pilots thinking? I know it’s different aircraft makers, but there could be a thought process of making sure you perform a proper stall recovery and pushing forward as opposed to constantly pulling back.

This report will make interesting reading purely from a human factors point of view. They really need to find the CVR.
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Old 7th Nov 2018, 12:16
  #722 (permalink)  
 
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So what would make this flight different?
Some maintenance was done in between. Which may have made things worse if curing the wrong symtoms...

This report will make interesting reading purely from a human factors point of view
I just hope real human factors specialists will be involved in writing it. For sure this will have many very interesting aspects.

I wonder if when the nose dropped each time, this motion caused an illusion that the aircraft had just entered an actual stall.
Especially as the reduction in g load would have been much stronger than any simulator can do, further creating confusion and raising adrenalin levels. The body of most persons reacts vilently to reduced g, and most large aircraft pilots experience it very seldom, not even in the sim.

You are incorrect that action led to a “massive control displacement.”
There has been an (still unexplained) rudder deflection, not large in numbers but still quite massive at cruise speed, which made things significantly worse.
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Old 7th Nov 2018, 12:22
  #723 (permalink)  
 
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"the angle of attack sensors were replaced"

ABC News reports that the AoA sensors were replaced before the second-to-last flight https://abcnews.go.com/International...laced-59028450

Also, from Channel NewsAsia

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.

https://www.channelnewsasia.com/news...nsors-10905532

Last edited by mross; 7th Nov 2018 at 12:40. Reason: added second report
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Old 7th Nov 2018, 12:38
  #724 (permalink)  
 
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The Boeing website is surprisingly clear...
The Indonesian National Transportation Safety Committee has indicated that Lion Air flight 610 experienced erroneous input from one of its AOA (Angle of Attack) sensors.
Quite a different issue compared to UAS...
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Old 7th Nov 2018, 12:46
  #725 (permalink)  
 
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Originally Posted by Volume View Post
The Boeing website is surprisingly clear...

Quite a different issue compared to UAS...
From my own experience on the NG a wrong AoA input will result in UAS, unreliable altitude, vertical speed, wind information and ground speed display. It is a basic correction factor into the ADIRU that does effect all resulting air data related information and surprisingly the non air data related information of ground speed as well. It might be different in the MAX, but somehow i doubt it. As different airflow over the fuselage results in huge position error values for static and pitot tube values, the AoA vane corrects those very different position errors, therefore a wrong AoA indication will result in a completely unreliable air data set.
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Old 7th Nov 2018, 12:52
  #726 (permalink)  
 
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Volume.

Quote:
You are incorrect that action led to a “massive control displacement.”
There has been an (still unexplained) rudder deflection, not large in numbers but still quite massive at cruise speed, which made things significantly worse.

<<<<<<>>>>>>

Mod please delete if this is too arcane.

UAS. Some interesting similarities here to another UAS that ended badly.

Subject a/c experienced UAS, followed by warnings and Stall Warning. Pilot initiated (mistakenly) Stall recovery for approach, not high altitude, pull back stick to maintain altitude and increase power. AP switched off, but the CVR audio had the sound of AP switch being cycled by pilot, which is prohibited by airframer. “might lead to control loading leading to failures”.

When found, Rudder showed position of four degrees right, the max deflection allowed by RTLU, (Rudder limiter). Flight path reconstruction showed chronic right roll, and drift, consistent with this deflection in rapid uncontrolled descent.

Pilots ignored Stall Warnings, (there were many).
Subject aircraft type had experienced unexplained and uncommanded nose overs, that were recovered, prior.

Basically a case of aircrew not being familiar with, or untrained for, aircraft “idiosyncrasies”? Different type from this one, but both started with UAS.

Subject accident had major Trim issue. Trim controlled by automatics, they missed it as Trim ended up Full Nose Up, seemingly unknown by crew.

UAS was less well mitigated back then. It didn’t even have an acronym, but needed to be written out tediously when referenced. “UAS” was first used in that discussion, probably by lazy typing averse poster?

Subject aircraft had no AoA (display) installed, and was without a standby Airspeed display, both available at delivery, but not purchased.

Much discussion of “just fly Pitch, and Power”.

Last edited by Concours77; 7th Nov 2018 at 13:05.
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Old 7th Nov 2018, 13:12
  #727 (permalink)  
 
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Boeing warns that the stabilizer system can reach its full downward position if not counteracted by pilot trimming the aircraft and disconnecting the stabilizer trim system.
All manufacturers build planes with anti-stall devices.Airbus goes a step further and actually wont allow the stall(normal law).Boeing just warns and aids the pilot to prevent it.Stick shakers,EFS,PLI,the old stick pushers,autoslat,automatic trimming nose down etc etc....all used to help the pilot not stall.All very useful devices.Until you get unreliable pitot-static data(incl AoA).Then these devices can work against you.
What can the pilot do?What can the manufacturer do?
The pilot must know when there is a mismatch between reality and perception(training....airmanship....alertness).The pilot must then follow the QRH memory items and religiously disregard the warnings,disable any stall protection system that affects flight control surfaces( and the only one here is trim) and fly the plane(really not that difficult).EFS doesnt affect flight control surfaces per se it just makes it harder to pull and easier to push.Shakers are tactile warnings.PLI and the like are visual warnings.In the B737 its just the trim thats now working against your control of the ac.
The manufacturer must install these anti-stall devices for certification but cant,as some wise soul above said,prevent pitot-static errors from occurring.Life isnt like that.Errors occur.
Until they come up with something better than the pitot-static system,all they can do is provide data to the pilots in the FCOM and QRH on how to recover from the situation.Somebody a while back posted a picture of a Fokker 100 center pedestal panel(right next to the pilots) showing circuit breakers for overspeed/shaker.This is a very nice design IMO.Its so nice that perhaps it should be an industry standard(with provision of course that switches be protected by covers that have to be flipped by the pilot before they can be activated.... as shown in the Fokker 100 photo)Even with training and good airmanship,the need for crews to disable spurious warnings(the loud aural and tactile warnings that add to confusion) is of paramount importance,especially so if the UAS event is of longer duration.The manufacturer can also refrain from burying pertinent data in the AMM and start to include it in the FCOM.
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Old 7th Nov 2018, 13:21
  #728 (permalink)  
 
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Originally Posted by Concours77 View Post
Quote:
You are incorrect that action led to a “massive control displacement.”
There has been an (still unexplained) rudder deflection, not large in numbers but still quite massive at cruise speed, which made things significantly worse.

Do we really know that there was a significant "rudder dieflection"? With airspeed just a bit above the maneuvering speed, a pull-up into a full stall is dangerous but semi-benign - it would cause the G force to exceed the rated 2.5G - but only briefly and not by much. But combined with a rudder deflection, it becomes a snap roll. A snap roll is not really a roll. It's a powerful horizontal spin.
I've done snap rolls in a Citabri with a header tank.
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Old 7th Nov 2018, 13:30
  #729 (permalink)  
 
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This appears to be a simple bent or bad AOA probe giving a erroneous stall warning. Poor jetway operation is the usual cause of a bent probe. I have had it on a L1011 and 727 plus several military aircraft. It’s a no brainer to handle on a non FBW aircraft. You know you are not stalling based on airspeed, attitude, power and phase of flight. Disconnect the electrical trim and fly the aircraft. When time permits pull the stick shaker circuit breaker. What is hard to understand is why over 4 flights this was not diagnosed or fixed. You wonder if the pilots or mechanics even knew the stall warning comes off the AOA probe.
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Old 7th Nov 2018, 13:45
  #730 (permalink)  
 
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Originally Posted by Sailvi767 View Post
. What is hard to understand is why over 4 flights this was not diagnosed or fixed. You wonder if the pilots or mechanics even knew the stall warning comes off the AOA probe.
Well, you're assuming that one of the symptoms was an unambiguous stall warning. I don't recall that it was written up in the trip log. from memory, I seem to recall the squawks were for an unreliable airspeed indication and an incorrect activation of the pitch trim. That's a little different than: "There we were, tooling along at M0.8, level at 360 and and suddenly the stall warning sounded and the stick shaker activated." That pretty clearly points to a possible AoA data problem, the way it was actually written up, much less so.
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Old 7th Nov 2018, 13:47
  #731 (permalink)  
 
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Originally Posted by Denti View Post
.... and surprisingly the non air data related information of ground speed as well.
Yes, that is surprising. How does AoA data affect Groundspeed, and why?
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Old 7th Nov 2018, 13:53
  #732 (permalink)  
 
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Boeing OMB Bulletin and 737 MAX vs NG?

Has anyone seen the Boeing issued bulletin?

The Boeing media room confirms such a bulletin has been issued: MediaRoom - News Releases/Statements

At this point I don't understand whether this is a MAX issue or a 737 recent generations issue (i.e. MAX and NG variants).

Any clarification appreciated.

- GY
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Old 7th Nov 2018, 14:17
  #733 (permalink)  
 
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Although not an (air) pilot I was an engineer. This one is entirely on the engineers. The AoA sensor was replaced the day before the fatal flight. I really should not have to expand on why flying passengers on a plane that has exhibited multiple critical failures of an unknown cause is a bad, perhaps even criminal course of action. This was being treated like a lemon car at a dealership is often treated -- "well, try replacing the sensors and see if that helps." That can be a bad idea even for a passenger car (and has led to lawsuits when the car crashes) but when you have hundreds of lives thousands of feet in the air it is beyond unacceptable. Even though the likes of Microsoft and Apple seem to have forgotten it, there is a thing called "testing" which you should do before a fix goes live. It is very easy to make things worse.
It was probably a bad wiring harness, and no amount of new sensors will fix that.
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Old 7th Nov 2018, 14:19
  #734 (permalink)  
 
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That "journalistic" website that doesn't like to cite sources claims to have posted the bulletin in question:
The Indonesian National Transportation Safety Committee has indicated that Lion Air flight 610 experienced erroneous AOA data. Boeing would like to call attention to an AOA failure condition that can occur during manual flight only.

This bulletin directs flight crews to existing procedures to address this condition. In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds. The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after the electric stabilizer trim switches are released. Repetitive cycles of uncommanded nose down stabilizer continue to occur unless the stabilizer trim system is deactivated through use of both STAB TRIM CUTOUT switches in accordance with the existing procedures in the Runaway Stabilizer NNC. It is possible for the stabilizer to reach the nose down limit unless the system inputs are counteracted completely by pilot trim inputs and both STAB TRIM CUTOUT switches are moved to CUTOUT.

Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:

- Continuous or intermittent stick shaker on the affected side only.
- Minimum speed bar (red and black) on the affected side only.
- Increasing nose down control forces.
- Inability to engage autopilot.
- Automatic disengagement of autopilot.
- IAS DISAGREE alert.
- ALT DISAGREE alert.
- AOA DISAGREE alert (if the AOA indicator option is installed)
- FEEL DIFF PRESS light.

In the event an uncommanded nose down stabilizer trim is experienced on the 737-8 /-9, in conjunction with one or more of the above indications or effects, do the Runaway Stabilizer NNC ensuring that the STAB TRIM CUTOUT switches are set to CUTOUT and stay in the CUTOUT position for the remainder of the flight.
In short, bad AOA data is sufficient to cause the reports of UAS and STS acting backwards. The maintenance writeups implicitly made a diagnosis, and it looks like nobody down the line went back to the causes and inferred the problem. For that matter, go back and read the discussion here and see what was said about the AOA sensors. It's still a head-scratcher.
And, to reply to a comment from pages above, no this is not a case where "just hand-fly" would be the worst thing to do. The sensor failure kicked off the automatics, and there was no choice. The guidance in the bulletin is a "reminder" of the procedure to follow if the aircraft is trying to trim the nose into the ground.
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Old 7th Nov 2018, 14:21
  #735 (permalink)  
 
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Originally Posted by Sailvi767 View Post
This appears to be a simple bent or bad AOA probe giving a erroneous stall warning. Poor jetway operation is the usual cause of a bent probe. I have had it on a L1011 and 727 plus several military aircraft. It’s a no brainer to handle on a non FBW aircraft. You know you are not stalling based on airspeed, attitude, power and phase of flight. Disconnect the electrical trim and fly the aircraft. When time permits pull the stick shaker circuit breaker. What is hard to understand is why over 4 flights this was not diagnosed or fixed. You wonder if the pilots or mechanics even knew the stall warning comes off the AOA probe.
Yes, except this article (from further up the thread) states that the "broken" AOA sensor was replaced. Apparently they are sending it back to mfr for examination, presumably to find out how it caused a crash whilst not even on the aircraft... Does seem to mean that the earlier leaked maintenance reports that didn't mention AOA sensor were at best misleadingly incomplete. Also there is the possibility that the wrong sensor got replaced, or multiple duff sensors.

From the same article we also have (in relation to previous flight):
"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,"
while on Boeing site it basically says "refer to existing procedures" - which is sort of implying that the crash pilots didn't follow them.

Also when comparing to L1011 & 727 era, need to remember that it's no longer three independent sets of sensors feeding three sets of gauges, but rather three sets of sensor inputs all going into multiple redundant ADIRUs which decide/calculate the "correct" data outputs, which can then be fed to either PFD. Any one sensor input being wrong could (by design, it shouldn't, but...) give incorrect or invalidated data on any output from any/all ADIRUs - it all depends on ADIRU internal logic. AF447 threw up some "interesting" ADIRU logic at high (actual) AOA, similar may apply at erroneously-high sensed AOA.
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Old 7th Nov 2018, 14:23
  #736 (permalink)  
 
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Originally Posted by Rananim View Post
The pilot must know when there is a mismatch between reality and perception(training....airmanship....
In this kind of event, "solving" the problem in the air with passengers on board is the wrong approach.
Better to disengage all automatic systems and fly manually until the flight is complete.
End of.
Fighting with the computer, which might or might not be working properly, or programmed properly, or the procedures which might or might not take into account this situation etc... this is a a game you will lose.
Uproot the problem land the plane, argue later.
In this era of .... a wish to reduce crew costs and bring in more computing .... with so many financial agendas behind the machines and procedures, simplify everything land the plane.
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Old 7th Nov 2018, 14:26
  #737 (permalink)  
 
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How does AoA data affect Groundspeed, and why?
Not groundspeed, but indicated airspeed....

In a nutshell: total pressure is constant wherever you have airflow, hence you can place a pitot tube at any location where you have attached airflow, if the probe roughly points into the airflow, it will work satisfactory.
Measuring static pressure only works in places, where the airflow has exactly the same speed as the aircraft. If you would measure static pressure on the upper wing surface, you would actually measure the low pressure which keeps you in the air. Also on the nose fuselage, you have slightly increased airflow speed, an your static pressure is too low. Towards the end of the fuselage your airflow may be more the same as the general airspeed, but the turbulent boundary layer of the fuselage would create some high frequency pressure variations. So it is very, very hard to find a proper place for the static probe.
If you place the static probe in a position where the additional speed due to the airflow around the fuselage is well known, you may correct the measured pressure electronically. This obviously happen here, static pressure measurement is AoA sensitive, so you measure AoA to correct your static pressure.
This way, an AoA failure results in unreliable static pressure, hence UAS and unreliable altitude. Additionally your AoA driven stall warning goes havoc...

Not so nice if you are sitting in row 0.
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Old 7th Nov 2018, 14:35
  #738 (permalink)  
 
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The way I read this is : Pilots May have had erroneous air data (caused by faulty AOA sensor) on one side, causing multiple miscompare messages.

Confusing start..

Autopilot may not have been available; the bulletin saying STS may continue to trim nose-down to prevent a stall condition during manual flight.

(With those messages why wouldn’t the software automatically inhibit the STS?)

Either a false stick pusher activated, or the crew was fighting an ever-worsening out-of-trim condition which resulted in enourmous stick forces they could no longer handle? Both?

All the above my speculation, of course.


Last edited by FIRESYSOK; 7th Nov 2018 at 15:51.
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Old 7th Nov 2018, 14:39
  #739 (permalink)  
 
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I've often wondered this, and maybe it could help: Why not go in to CWS when faced with UAS? Set the pitch (4deg or 10deg) via CWS and set the N1 (75% or 80%)?
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Old 7th Nov 2018, 14:41
  #740 (permalink)  
 
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Please remember this if you are one of the many fine Men and Women whom I sometimes trust with my life. A failure in a new plane is an even more serious matter than a failure in an old one, and you should refuse to fly it until the flaw with the plane -- and how confident you are that they have really discovered the true flaw --- is explained to your satisfaction. This is true of any complex system; each successful "flight" is a proof that there isn't a large underlying flaw in the construction. A 30-year-old house that shows drywall cracking and uneven floors is a far different matter than a one-month-old house with exactly the same symptoms to the same degree. There is a lot of stuff on a plane that will never go wrong if it was initially assembled correctly, so there really are not procedures to deal with an incorrect assembly.
Unless you always fly by hand, a programmer could design avionics that could kill the best of you. Obviously the engineers try very hard to keep people alive rather than kill them, but there is this guy called "Murphy" lurking in the background. One person in South Carolina has a bad day and puts the blue wire in the red slot or maybe a knife slips and "whew! It looks good, I don't have to redo that entire bundle" and the air gap between the wires is large enough that it doesn't cause a short on the dry day that the plane was tested...
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