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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 13th Nov 2018, 11:54
  #1081 (permalink)  
 
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Originally Posted by phil gollin View Post

[...] a single (?) AOA sensor failure [...] SEEMS to have activated the stick shaker

[...] there were two AOA sensors on the plane, so how did the FCS decide which one was at fault ?

[...] a failed AOA sensor causing one-sided stick-shaker operation seems optimistic.
This misconception has been floating around for long. The stick shaker is not an annunciation of a sensor failure.

It is the normal approach-to-stall warning triggered by a high AoA value. It does not know that that high AoA value is wrong, but for stall warning it is better to be safe than sorry, so the two stick shakers apparently are independent, and each each rely on the AoA probe on their respective side of the aircraft. Which makes perfect sense from a redundancy and failsale-design standpoint. If two AoA sensors disagree, don't try to be smart and figure out which might be wrong. Just activate a stick shaker on a high value. In most cases it is preferable to have a spurious stall warning when there is no stall, than not to have a stall warning on a real approach to stall.


TL;DR: A "failed sensor" did not activate the stick shaker. A high AoA value did.

Bernd
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Old 13th Nov 2018, 12:11
  #1082 (permalink)  
 
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Originally Posted by phil gollin View Post
IF they had had, say, three AOA sensors, then at least the electronics could have "voted" two-to-one which were correct and which "failed".
The A320 has three AoA sensors.

That just meant, in the Perpignan crash, that the two frozen ones outvoted the working one ...
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Old 13th Nov 2018, 12:22
  #1083 (permalink)  
 
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Originally Posted by Derfred View Post
A key question of the crew reaction is “were they following the Airspeed Unreliable checklist?”.

From the FR24 data, it appears that they were not. There is no attitude and thrust data in the QRH that provides level flight at 5000 feet at approx 300 knots. (Not on the NG anyway.)

So what were they doing?

If they were flying “an” attitude and thrust, that would automatically include manual trim, which would eliminate the MCAS issue, with a possible manual trim input every 5 seconds required.

Presumably you could only have arrived at that conclusion on the latter point to eliminate MCAS, if you believe in manual reversion that they had set the stab trim cutout to CUTOUT as per the AD?
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Old 13th Nov 2018, 12:48
  #1084 (permalink)  
 
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Originally Posted by glad rag View Post
​​​​​Absolutely.

How did Boeing push these aircraft through certification without through oversight.

Do they get dispensation to do it themselves??
They essentially self-certify. The FAA wouldn't know how.
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Old 13th Nov 2018, 12:52
  #1085 (permalink)  
 
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Originally Posted by glad rag View Post
​​​​​Absolutely.

How did Boeing push these aircraft through certification without through oversight.

Do they get dispensation to do it themselves??
Without a complete investigation we don't have the facts to point to an inadequate certification.

We should revisit this a year from now. Meanwhile make sure the AD reasonably protects us while we answer this question
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Old 13th Nov 2018, 13:17
  #1086 (permalink)  
 
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The automated stall-prevention system on Boeing 737 MAX 8 and MAX 9 models—intended to help cockpit crews avoid mistakenly raising a plane’s nose dangerously high—under unusual conditions can push it down unexpectedly and so strongly that flight crews can’t pull it back up. Such a scenario, Boeing told airlines in a world-wide safety bulletin roughly a week after the accident, can result in a steep dive or crash—even if pilots are manually flying the jetliner and don’t expect flight-control computers to kick in.
Boeing doesnt design its FCCs with a psycho mode.Qantas 72 isnt possible in a Boeing.The poor travelling public probably think the FCC forced the Lionair into a dive.It didnt.It trimmed the aircraft nose down in response to faulty AoA....the report from the previous commander clearly says "STS trimming the wrong way".The pilots just have to recognize that they are facing unreliable data,disengage the automation,disengage the AP stab trim motor and fly the plane using basic attitude/thrust combinations.
Unfortunately,it appears that the accident crew became a bit saturated and just played tug of war with the opposing trim until time ran out.Startle factor/panic reduces cognitive faculties.The continuous stick shaker activation will contribute greatly to that startle factor.

The A320 has three AoA sensors.

That just meant, in the Perpignan crash, that the two frozen ones outvoted the working one ...
See how difficult it is to design perfection?
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Old 13th Nov 2018, 13:20
  #1087 (permalink)  
 
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Originally Posted by fdr View Post
As an industry we don't cope well with sensor failures, and as systems become more integrated the problem will grow...
Tightly integrated systems can overwhelm a crew when a sensor failure occurs -- especially when the package of simulator anomalies used in training hasn't included the (unanticipated and poorly documented) condition.

Should "better/more training" remain the sole remedy?
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Old 13th Nov 2018, 13:35
  #1088 (permalink)  
 
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Originally Posted by phil gollin View Post
.

Going back a bit ...... the problem SEEMS to have arisen due to a single (?) AOA sensor failure. This then SEEMS to have activated the stick shaker on the side of the aircraft associated with that failed sensor , which happened to be the PF's side (correct ?) In addition this single failure then gave rise to the MCAS starting the POSSIBLE disastrous changes in trim.

IF that is basically correct.

1: It has been stated on here that there were two AOA sensors on the plane, so how did the FCS decide which one was at fault ? IF they had had, say, three AOA sensors, then at least the electronics could have "voted" two-to-one which were correct and which "failed".

2: Whilst the stick-shaker seems to have been a warning there has been no mention (I may have missed it) of any particular flashing button, or message on a glass screen coming up to note that a particular AOA sensor had failed. I note that there will always be a problem with overloading pilots with information when there is an emergency but asking overloaded pilots to remember the possibility of a failed AOA sensor causing one-sided stick-shaker operation seems optimistic.
I am an avionics maintenance engineer. I have not worked on any model of the 737, but am very familiar with AOA systems on a variety of other transport category aircraft.

If the probe dropped offline completely - stopped sending any position data to the aircraft systems - that would usually trigger some kind of CAS message to indicate a failure of the probe has occurred. On all aircraft I am familiar with, this would also trigger a warning that the stall warning and protection system is degraded. A single AOA probe can trigger the stick shaker if it senses high alpha, but normally both probes have to be in agreement as to the high alpha to trigger the stick pusher. With a failed probe, you would not have the pusher function available.

The MCAS system is a new concept to me. I would think that in a well-designed system, you would want to have agreement as to current AOA from BOTH probes before automatically applying nose down trim, just as with the voting required to activate the pusher on every aircraft model I have worked on.

In this incident, it appears that the left probe was still sending data, thus no “AOA fail” message - but the AOA data from the left probe appears to have been massively different than that from the right side.

I do not have access to a 737 Max AMM, so do not know the post-installation functional checks required after replacing a faulty probe. Most probes contain a guide pin which inserts into a matching hole in the fuselage to insure that the probe body is physically oriented correctly in relation to the airframe, but on all aircraft models I work on, installing a new probe also requires a post-install rigging check to insure that the output position data is correct. Typically this is done with a rigging adapter that attaches to the probe and fuselage, containing a calibrated angle scale and pointer, and a mount to attach a calibrated digital protractor. The check usually involves rotating the probe to specific angles, while checking the generated data to insure it is accurate.

IF the 737 Max requires a rigging check when an AOA probe is replaced, the question is: did the Lion Air engineers perform one, or did they just replace the probe and sign it off? A rigging check would have revealed any inaccuracy in either the new or old probes. If no rigging check is required in the AMM procedure for replacing an AOA probe, then that is on Boeing, not Lion Air.

An AOA rigging adapter is a precision piece of test equipment that has to be calibrated and certified. A large airline would likely have one on hand, a smaller airline not so likely.
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Old 13th Nov 2018, 13:43
  #1089 (permalink)  
 
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Originally posted by bsieker: If two AoA sensors disagree, don't try to be smart and figure out which might be wrong. Just activate a stick shaker on a high value. In most cases it is preferable to have a spurious stall warning when there is no stall, than not to have a stall warning on a real approach to stall.
Agreed, except that perhaps the authority of the MCAS should be limited if only one of the two AoA systems outputs a high value.
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Old 13th Nov 2018, 13:46
  #1090 (permalink)  
 
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Originally Posted by Zeffy View Post
Tightly integrated systems can overwhelm a crew when a sensor failure occurs -- especially when the package of simulator anomalies used in training hasn't included the (unanticipated and poorly documented) condition.

Should "better/more training" remain the sole remedy?
Good question, but we know the answer before it was asked. The answer? Yes.

Case in point? Batteries in a to-go box. Duct tape and twine, simples.

The alternative: grounding, refit, reprise certification, punish those who deliberately isolated safety critical data from operator group.

Heads will not roll. Boeing owns the guillotine, and it is placarded “Inop”.

just sayin’

Last edited by Concours77; 13th Nov 2018 at 15:51.
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Old 13th Nov 2018, 13:51
  #1091 (permalink)  
 
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Originally Posted by Rananim View Post
Boeing doesnt design its FCCs with a psycho mode.Qantas 72 isnt possible in a Boeing.
That's really the epitome of double-think: "This airplane crashed and killed almost 200 people because of a Boeing system idiosyncrasy, but Boeing is better than Airbus, because this other accident of an Airbus which only injured a few people."

You do realise that this Boeing aircraft behaviour is deliberate, whereas the problem with Qantas Flight 72 was a software error (what some people call a bug: i. e. the opposite of "designed")?

You realise further, I hope, that there are good reasons for having the system put in nose-down commands when approaching the stall angle of attack?

I'm not normally one to pit the aircraft manufacturers against each other, I know they all have their problems, but this kind of fanboyism has gone too far.

The pilots just have to recognize that they are facing unreliable data,disengage the automation,disengage the AP stab trim motor and fly the plane using basic attitude/thrust combinations.
(my emphasis)

Right. "Just ...". That's easy.

P. S. Your posts would be a lot more readable if you put a blank space behind punctuation marks.
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Old 13th Nov 2018, 13:57
  #1092 (permalink)  
 
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Originally Posted by Gysbreght View Post
Agreed, except that perhaps the authority of the MCAS should be limited if only one of the two AoA systems outputs a high value.
Perhaps. I'm not judging the MCAS either way, I was just trying to clear up the misconception that the stick shaker was designed to be used as a failure indicator, whereas here it was just an inadvertent symptom among many.
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Old 13th Nov 2018, 13:58
  #1093 (permalink)  
 
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Originally Posted by Concours77 View Post

Except that the “augmentation” works in opposition to manual control “feel”. Making it the opposite of enhancement or augmentation.

Sounds like low stick force isn't the quality they wanted enhanced, but rather the opposite. It's not an aerobatic plane, but an airliner; so high stick force at high AOA to prevent stall is desired.

By the way, the Artificial Horizon locates the nose, and can be used to suss AoA from FPV, no?

cheers.
I don't know what you mean by "locates."
The difference between nose and horizon is attitude.
The difference between nose and FPV (wind notwithstanding) is AOA.
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Old 13th Nov 2018, 14:02
  #1094 (permalink)  
 
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Boeing withheld info on the Boeing 737 Max 8 and 9

Boeing Co. withheld information about potential hazards associated with a new flight-control feature suspected of playing a role in last month’s fatal Lion Air jet crash, according to safety experts involved in the investigation, as well as midlevel FAA officials and airline pilots.

The automated stall-prevention system on Boeing 737 MAX 8 and MAX 9 models—intended to help cockpit crews avoid mistakenly raising a plane’s nose dangerously high—under unusual conditions can push it down unexpectedly and so strongly that flight crews can’t pull it back up. Such a scenario, Boeing told airlines in a world-wide safety bulletin roughly a week after the accident, can result in a steep dive or crash—even if pilots are manually flying the jetliner and don’t expect flight-control computers to kick in.
---Wall Street Journal

https://www.wsj.com/articles/boeing-...ers-1542082575
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Old 13th Nov 2018, 14:11
  #1095 (permalink)  
 
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Originally Posted by Towhee View Post
---Wall Street Journal " Boeing Co. withheld information about potential hazards associated with a new flight-control feature suspected of playing a role in last month’s fatal Lion Air jet crash, ..."
Point of order; they didn't just withhold information on the "potential hazards associated with a new flight-control feature", they withheld information of the very existence of the "new flight-control feature".
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Old 13th Nov 2018, 14:28
  #1096 (permalink)  
 
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Well it looks like my question: "is there another system that's supposed to be automatically moving the trim prior to 10 seconds?" has been answered. Thanks Boeing!
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Old 13th Nov 2018, 14:38
  #1097 (permalink)  
 
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Hi. Aren’t the boxes constructed to keep sea water OUT of the interior? I can see washing the box to flush salt a couple times, but soaking? An example would be AF447? After TWO years in salt, the boxes were undisturbed by corrosion. At a depth of 4000 meters?
You dont know if the box has been damaged and salt water has gotten in.
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Old 13th Nov 2018, 14:44
  #1098 (permalink)  
 
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fish

Originally Posted by underfire View Post
After TWO years in salt, the boxes were undisturbed by corrosion. At a depth of 4000 meters?
At 4000 meters depth-little- no oxygen-Corrosion is related or equal to OXIDATION which requires . . . Oxygen...

Last edited by CONSO; 13th Nov 2018 at 14:46. Reason: spelling
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Old 13th Nov 2018, 15:43
  #1099 (permalink)  
 
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Originally Posted by CONSO View Post
At 4000 meters depth-little- no oxygen-Corrosion is related or equal to OXIDATION which requires . . . Oxygen...
Think “electrolysis”. Corrosion is not the only hazard.
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Old 13th Nov 2018, 15:48
  #1100 (permalink)  
 
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Originally Posted by Vessbot View Post
Sounds like low stick force isn't the quality they wanted enhanced, but rather the opposite. It's not an aerobatic plane, but an airliner; so high stick force at high AOA to prevent stall is desired.


I don't know what you mean by "locates."
The difference between nose and horizon is attitude.
The difference between nose and FPV (wind notwithstanding) is AOA.
Trying to make a point here. Attitude is displayed as degrees above/below Horizon. FPV displays degrees above/below horizon. Consolidating both elicits AoA. No? You brought up wind, I didn’t.

ALSO. “Augmentation” does not assist input. It works independently of crew handling.

It is not installed to assist manual handling. It is installed to protect the aircraft from the crew, just as shaker/pusher does. Except, as here in Lion Air, it loses the plot and destroys the aircraft, crew and all the souls on board.

Last edited by Concours77; 13th Nov 2018 at 15:59.
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