Indonesian aircraft missing off Jakarta
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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.
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.
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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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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.
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 ...
That just meant, in the Perpignan crash, that the two frozen ones outvoted the working one ...
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Should "better/more training" remain the sole remedy?
.
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.
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.
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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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.
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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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.
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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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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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.
cheers.
The difference between nose and horizon is attitude.
The difference between nose and FPV (wind notwithstanding) is AOA.
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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.
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.
https://www.wsj.com/articles/boeing-...ers-1542082575
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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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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?
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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.
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.
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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Silver
Last edited by silverstrata; 13th Nov 2018 at 16:10.