Indonesian aircraft missing off Jakarta

[DaveReidUK]

Originally Posted by threemiles

This is nonsense. Certification is a desktop exercise. You go through the aircraft systems schematics and make a risk analysis about what if then. It is not about trying to let something emerge.

You're not making sense. No, of course it isn't about that. By definition you can't "try to let something emerge" if you don't know it exists.

But it happens. If you're suggesting, as you seem to be, that certification doesn't involve flight testing, that's clearly nonsense.

Flight Test Guide for Certification of Transport Category Airplanes - FAA

[bsieker]

Originally Posted by rideforever

I can only see more and more such incidents occurring.
[...] you have to engage the subconscious animal (who understands physical reality)

[...]

Sullenberger, when he saved his place, reverted to the subconscious animal (who feels physical reality)

The "animal" in humans does quite definitively NOT understand or feel the physical reality of three-dimensional flight. Not even close.

I recommend this report by the ATSB about spatial disorientation to learn about the many ways the animal mind will get it thoroughly and dangerously (and often fatally) wrong. We are not birds (and even they will get it wrong, they just don' make the news).

If I was a pilot, in such a situation, I would
[...]

No you wouldn't.


Bernd

[CYTN]

Again , I am just curious . If they replaced a sensor should this show up on the maintenance log ? , I cannot see it . I see fushing and testing but no reference to a replacement part . Also my point as regards fitting a different part type , I was not specifically hinting at a copy but rather using a similar part that may be considered an acceptable replacement if the exact matched part was unavailable at the time .

[A Squared]

Originally Posted by CYTN

Again , I am just curious . If they replaced a sensor should this show up on the maintenance log ? , I cannot see it . I see fushing and testing but no reference to a replacement part . Also my point as regards fitting a different part type , I was not specifically hinting at a copy but rather using a similar part that may be considered an acceptable replacement if the exact matched part was unavailable at the time .

Agree. I don't see anything on the aircraft log that indicates a part was replaced. It seems like I recently read that the AoA sensor was replaced on flight prior to flight immediately before the accident flight.

Edit: Now I'm scratching my head. I was trying to verify where I read that the AoA sensor wasn't replaced on the DPS-CGK flight shown on the log page, but on a prior flight, and it seems I read it in a post you made.

Originally Posted by CYTN

KNKT states AoA sensor replaced on 28TH Oct prior to JT43 flight to Jakarta . but that flight still had issues . So was the sensor probe not the core issue . Could it have been an issue with the mounting . Or something else beyond this . Could the sensor that was replaced be a different part type to the origional . Just asking those of better understanding .

[Gary Brown]

Originally Posted by Bleve

Ever since AF447, 'IAS Disagree' has been front and centre of emergency training. Quite possibly on this flight the AOA issue generated an IAS Disagree message and the crew (quite reasonably) carried out the IAS Disagree checklist. The first step of which is to disconnect the autopilot and fly manually. Now the door is open for the uncommanded stab trim problem to rear it's ugly head.

At assorted points in this thread we've wondered whether the Memory/QRF section for an IAS Disagree included an alert about the StabTrim issue, or whether it's in a separate Memory/QRF section. What I've seen so far suggests that the Runaway StabTrim in Manual Flight issue is NOT mentioned in the IAS Disagree section - but I've not really seen the QRF for this exact model of 737. Anyone?

[DaveReidUK]

Originally Posted by A Squared

Agree. I don't see anything on the aircraft log that indicates a part was replaced. It seems like I recently read that the AoA sensor was replaced on flight prior to flight immediately before the accident flight.

Edit: Now I'm scratching my head. I was trying to verify where I read that the AoA sensor wasn't replaced on the DPS-CGK flight shown on the log page, but on a prior flight, and it seems I read it in a post you made.

The AoA sensor was reportedly replaced at Denpasar on 28th October during the 12 hours that the aircraft was on the ground there. That action would be recorded on the tech log for the Manado-Denpasar sector, either as an action taken in response to a snag raised by the crew on that flight or as a maintenance entry.

AFAIK, we haven't seen the tech log for that sector, only that for the subsequent Denpasar-Jakarta sector. So the log page where the AoA replacement is recorded isn't in the public domain, nor should we necessarily expect it to be.

[CurtainTwitcher]

So a plausible scenario for the crew faced based on the Boeing Bulletin is:

• At or soon after rotate, so message like "IAS disagree", possibly other messages and warnings, possibly even stick shaker.
• Manually flying so no autopilot to drop out.
• As they are manually flying, and trimming, the runaway stabilizer fault is masked and dealing with the unreliable airspeed.
• Probably running the unreliable airspeed memory items
• After not trimming for 5 seconds, STS trims nose down, PF counteracts with nose up pitch and trimmed, runaway trim is masked for 5 seconds.
• As they are solving the UA checklist, speed is increasing, air loads on horizontal stabilzer increase.
• A series of sequences of manual trim, 5 sec delay, then runaway stab, manual pitch up and trim, ratcheting down the stabilizer, pilots compensate with
• Eventually the speed increases and air load becomes so large, that both pilots are unable to overcome the nose down stabilizer trim all the way forward becoming unrecoverable as there is a further rapid increase in speed.

Basically in this type of scenario, the crew are confronted with an intermittent runaway stabilizer in addition to a UA. This intermittency is a difficult problem to nut out in the cacophony of noise and confusion of an unreliable airspeed scenario. Ironically, it may be possible they may of actually had three valid IAS indications, in close agreement, further heightening the confusion.

[birdspeed]

Perhaps, it would be a good idea to put ‘stab cutout’ into the memory items for the UAS checklist on the Max.

[mross]

Feel Diff Press light

Originally Posted by Hi_Tech

The Feel computer has two channels and they independently regulate the two different HYD source pressures to do the job in this sytem. If there is a difference in he two channels metered HYD pressure above a set value (I think it is 25%, I cannot recollect), you get an 'Elev Feel Warning'. That is so in B747. So I will assume it is same in B737. A faulty AOA sensor can make the Elev Feel Computer malfunction also.
Hope that makes sense?

Feel Diff Press

But there was no report of hydraulic pressure falling. So could the Feel Diff Press have illuminated due to elevator pitot disagree? The disagree, itself, triggered by a faulty alpha vane?

[Lord Farringdon]

Originally Posted by threemiles

How can "Automatic disengagement of autopilot" be an effect from AOA disagree, if the failure condition "can occur during manual flight only"?

The bulletin highlights nose down stabilizer trim due to erroneous AOA in manual flight only. That's what the bulletin is about. But it also mentions some other things that erroneous AoA can be responsible for including disengaging the AP. Logically, I take that as meaning that erroneous AoA effects can occur in any control condition one of which may be when in AP mode. Erroneous AoA affects both flight control regimes, but as a result of AoA erroneous data, nose down stabilizer trim will only occur in manual flight. Happy to be corrected by anybody who knows more about these things than I do.

[A Squared]

Originally Posted by DaveReidUK

The AoA sensor was reportedly replaced at Denpasar on 28th October during the 12 hours that the aircraft was on the ground there. That action would be recorded on the tech log for the Manado-Denpasar sector, either as an action taken in response to a snag raised by the crew on that flight or as a maintenance entry.

AFAIK, we haven't seen the tech log for that sector, only that for the subsequent Denpasar-Jakarta sector. So the log page where the AoA replacement is recorded isn't in the public domain, nor should we necessarily expect it to be.

Agree with all that. the "scratching my head" was about CYTN asking a question to which he appears to have supplied the answer in a prior post. No matter, at least it clarified in my mind when the AoA sensor was replaced.

[FullWings]

At assorted points in this thread we've wondered whether the Memory/QRF section for an IAS Disagree included an alert about the StabTrim issue, or whether it's in a separate Memory/QRF section. What I've seen so far suggests that the Runaway StabTrim in Manual Flight issue is NOT mentioned in the IAS Disagree section - but I've not really seen the QRF for this exact model of 737. Anyone?

A good question.

Imagining what the crew might have been be faced with on takeoff, it looks like at some point they probably had the symptoms of UAS: differing airspeed indications including warnings of the same. The AML entries for the previous flight(s) would have been a factor in the diagnosis, as was the limited time available to reach an initial conclusion and do something about it. Would you expect the aircraft to be exactly in trim? Not really as you don’t know for sure what your airspeed actually is. Are there indications of anything else that might be wrong that needs to be addressed *right now*, considering the workload already present? Well, there are some clues but it would take a lot of dot-joining and spare capacity.

To me, the killer is that, in general, the trigger for isolating the stabiliser in most aircraft is a warning that the stabiliser is out-of-control and/or the pilot detecting continuous stabiliser motion. It is likely that *neither* of these triggers was present because a) the system was working as designed (no warning) and b) the stabiliser motion was likely intermittent and reversible and with UAS you’d be expecting varying trim loads until you reached a steady state.

This is total speculation but looking at it from a HF perspective, I suspect that the primary task of controlling the airframe was challenging enough that they didn’t get very far along the road of analysing the problem before it overcame them...

[Clandestino]

Originally Posted by Vessbot

In the possible scenario where it suddenly takes 4 hands to hold the nose up (like what is being speculated here) it would certainly still be a problem.

I really can't imagine anyone, anywhere designing the synthetic feel system that requires four hands to hold the nose up and than having it certified. Running out of pitch authority is another matter.

Originally Posted by gums

We pilots should not have to memorize and obey 5 layers of control laws and such when things go awry. A backup law and maybe one more with zero "help" from Hal could be a realistic approach. But to see a buncha layers, go see the Airbus sequence.

So, when your LEF folded, did you consider the intricacies of the Viper's aerodynamics and FBW or you just countered the unwanted roll? Airbus is just the same. Control gains and effects may vary but if the attitude doesn't follow pılot's inputs it's not just FBW that got shot.

Originally Posted by gums

Unless your plane is a pure FBW, unstable design such as I flew, then it seems to me we should have some means to quickly and effectively revert to a pure "hand flying" machine if it passes all the agency certification requirements.

Well, that is exactly the issue: the oh-so-pilot-friendly-and-simple-and-manual 737 doesn't pass pitch stability certification criteria without constant supervision and intervention of STS HAL.

[Mac the Knife]

"...the oh-so-pilot-friendly-and-simple-and-manual 737 doesn't pass pitch stability certification criteria without constant supervision and intervention of STS HAL...".

Then it isn't simple and it isn't manual.

Very glad that I am not a pilot and obliged to operate a machine with so many possible unclear reversion states.

Mac

[CYTN]

DaveReid Uk ; A Squared .
Thanks for clearing that up for me .
So New sensor is fitted after they land at Denpasar and logged against that flight JT775 .
They then make flight Denpasar to Jakarta flight JT 43 and there is control issues again apparently associated with the same ( changed out sensor ) so they troubleshoot by the 'book' and purge out and test the new sensor , ( why purge out a brand new sensor ) ? - cause the book says that is procedure - Then they clean up some canon plug and test ( again book procedure ? ) . Then access and do a compartment inspection . ( book ? ) . Log detail in maintenance log for flight JT43 and sign off .
But the issue is not clear cut fixed and alarm bells are sounding so they dispatch a teckie on the fatal flight to monitor and further troubleshoot .
Would the Flight Crew be aware of the new fitted sensor and the fact that it had not corrected the issue or would he only be made aware of the tech log and fixes taken for JT43 flight .
Again I would expect that all tech logs for the aircraft would be put up on a server for maintenance to access at least .
Why would they authorise aircraft clearance to fly when the problem never went away after fitting the new sensor .
Mind Boggling. No wonder what happend ocurred coupled with the other control issues . Poor People .

[DaveReidUK]

Originally Posted by CYTN

They then make flight Denpasar to Jakarta flight JT 43 and there is control issues again apparently associated with the same ( changed out sensor ) so they troubleshoot by the 'book' and purge out and test the new sensor , ( why purge out a brand new sensor ) ? - cause the book says that is procedure

No, there is no explicit reference in the log for the DPS-CGK flight to an identified AoA sensor issue during the flight, nor any mention of it in the recorded rectification action, which only refers to the pitot and static Air Data Modules and the Elevator Feel Computer.

[Union Jack]

Originally Posted by MartinAOA

People like Gums can afford it :Interview with Lt. Col. Pat "Gums" McAdoo (Ret)

BTW, thank you for your service, Gums!

....and thank you, Hans Brinker, for the unintended consequence of highlighting Gums's outstanding record!

Jack appreciates.....

[Snyggapa]

Originally Posted by Centaurus

Extract from the Aeroperu Boeing 757 CVR 1996 crash with static vents blocked (English translation)
https://web.archive.org/web/20030427.../183038-1.html
One wonders if the Lion Air crew found themselves in the same state of confusion. Sensory overload can overwhelm rational actions every time.

Reading that transcript it is terrifying. You can almost feel the panic on the flight deck, and once one of the crew panics / becomes fixated on a certain aspect the other seems to have little chance of holding it together. Apart from all of the cockpit warnings going off, their attention is constantly being drawn to whatever the other crew is highlighting as being wrong at that moment. I don't envy anyone in that situation.

[alf5071h]

edmund #876, gums,
“ … reluctance in the industry to realistically quantify the expectation that a crew will be able to follow a recovery procedure.”
Not only the reluctance, the inability to quantify due to the inherent unpredictable human condition, because activity is heavily biased perception - the event at the time, etc, etc.

The industry increasingly appears to favour using a model of how technology works, or should work, (tech / certification), but when events show otherwise then instead of updating the model and changing the system the industry looks to ‘change the human’ - to match (mitigate) the errant tech model with more training.
We cannot expect pilots to manage technical failures in real time which are difficult to define in design or check in certification, or those which exceed the certification requirements (25.1302).

The interim procedure (AD) is full of assumptions. The background information frames the situation explaining the need for a new drill based on encountering an un-commanded nose down change of trim - education, training, simulation, (would a simulation show all of the other distracting features, or just a change in trim).

However, the inflight reality in manual flight (flaps up ?), the PF (failed side) could be more concerned by the stick shaker and speed indications, and distracting system alerts. Detecting a trim malfunction depends on a change in stick force (perhaps initially relating this to elevator opposed to trim). Potential for confusion, selecting an inappropriate drill / recovery action, etc, …

Conversely if the failure is on the PNF side, then further confusion - “what are you doing” CRM communication - totally different situations depending on displayed information, (no stick force), may choose unrelated checklist - UAS; incorrect mindset, difficult to change. (Similar to the Swedish CRJ)
Add surprise and continuing startle effect because of the apparent inability to control the aircraft or that the initial action did not work - where next …
The AD like the tech system is based on the same model; it assumes that the pilot will manage. (an assumption also seen in AF447, 20+ preceding events, AMS 737, ‘there is a drill for that’ - at higher altitudes)
………………

Oh, … and without AoA failure, inadvertently approaching a stall, - stick shake, low seed awareness, change in stick force (STS), misdiagnosed as a trim malfunction (salience of recent events), might a crew ‘inadvertently’ pull up, disconnect trim, etc, stalling the aircraft.
Little consideration of the human condition, their limitations in performance related to understanding of the situation; how we make sense of situations, in real time; AD - an assumption too far.

[GarageYears]

Just reading the thread is making me nervous....

Perhaps I am missing something here as this technical discussion is quite esoteric but Boeing advise ...."failure condition that can occur during manual flight only." The bolding from Boeing.

So all this discussion around pilots being under skilled and not being able to sort out an issue after disconnected the AP becomes even more interesting as the FCOM bulletin suggests that if the AP was flying the issue would have been resolved? Perhaps there is more significant information to come, perhaps once the FDR information has been released. At this stage it is about PR departments getting in with their version to bias the discussion to suit corporate aims.

And

How can "Automatic disengagement of autopilot" be an effect from AOA disagree, if the failure condition "can occur during manual flight only"?

I'm a little bothered here. I truly believe most here are smart and understand systems analysis at least enough to comprehend what the Boeing AD is telling us here, but the statements above have me frowning. Is this really so confusing?

Boeing states that a failure of an AOA sensor can cause the AP to kick off or not be select-able in the first place if the AOA was already iffy. So let's assume that happened here. The crew took off things seemed fine, but once in the air they either engaged the AP which then dropped out, or were unable to engage the AP due to AOA disagreement. So no automatics. The AD is referring to stabilizer trim under control of the flight control computer, which with an iffy AOA input will cause nose down trim to be applied in increments lasting up to 10 seconds, while in manual flight.

They HAVE TO BE in manual because the very condition the AD refers to disables the autopilot.

So, no more "if only they turned on the AP", right?

- GY