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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 1st Dec 2018, 13:59
  #1861 (permalink)  
 
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Hi_Tech;

Well, #3, flying the plane manually was "given". The aircraft flying with IAS disagree and ALT unreliable will have the autopilot automatically turned-off.

#2 was vaguely described in the log. Not knowing it was MCAS [or even its existence] doing its job, they thought it was a malfunctioning STS going the wrong way due to speed difference, so they wrote it that way in there.

#1, on the other hand, the BIG ONE- the stick shaker, their failure to mention it, in the log or to the MX, is likely to become one of the major focus for the investigation.
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Old 1st Dec 2018, 14:00
  #1862 (permalink)  
 
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Southwest fits all its Boeing 737 MAX planes with new safety device to avoid a repeat of the Lion Air crash that killed 189 people

Lion Air crash: Southwest adds safety device to planes to avoid repeat - Business Insider
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Old 1st Dec 2018, 14:46
  #1863 (permalink)  
 
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Originally Posted by silverstrata View Post


A high speed stall is not the same, as the elevator will still have a lot of authority at those higher speeds. MCAS was designed for a slow speed stall, when engine thrust combined with engine aerodynamic pitch-component, could and would exceed elevator authority and send the nose skywards. The MCAS is an anti home-sick-angel device.

The trouble is, as soon as it lowers the nose and gains speed, MCAS turns into a super gravitational attractant. Unless you can take all that forward trim off in a few seconds, your shiny 737 becomes a Stuka in terminaI dive mode. I still have no idea how anyone certified a device that would give a slippery passenger jet, full forward trim. And give that trim, when the aircraft is likely to end up 20 degree pitch down, and gaining speed rapidly.

Especially when the QRH (and I presume the Max QRH) says do not use too much trim in an incipient stall, as the aircraft may become uncontrollable. Actual wording for the approach to stall is:



And yet that is exactly what MCAS is giving you. I fail to see how Boeing can dodge this important issue, and not be forced to make major amendments to the MCAS system. At the very least MCAS should stop trimming at a safe point where a recovery from a dive is still possible - say 3-units on the trim indicator....!!

Silver

Edit: As to Zzuf’s question about why not fit a stick-pusher instead, I suspect this was a certification issue. If Boeing had admitted a stick-push was required, then a lot more certification would also have been required. But if you slip in a trim-pusher by the back door, then perhaps nobody will notice....

.

It seems as though it was designed for steep turns also. I'm guessing that the test pilots rolled and pulled and then they didn't have to pull so hard or had to neutralize as the engines aero effect added pitch input. "The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors"
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Old 1st Dec 2018, 14:56
  #1864 (permalink)  
 
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What would have been a proper design if the engine is of different size from previous generation. Does it need new wing/wingbox or MLG. Just trying to understand why Boeing come up with the band-aid fix called MCAS. Why didn't the modelling show there will be issues. Can't believe they didn't notice issues until test flight.
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Old 1st Dec 2018, 15:03
  #1865 (permalink)  
 
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re stick "nudgers" and stick pushers

Stick pushers are sometimes fitted when there are "stability issues approaching the stall" - in such a case, though, in order to fix such issues the pusher needs to be set to trigger BEFORE the adverse characteristics are manifest, with attendant likely adverse impact on stall speeds. A pusher can also sometimes be fitted when the characteristics AT the aerodynamic stall are acceptable, but the post-aerodynamic stall characteristics degrade so quickly that a "barrier" is required to prevent excursions into an unsafe zone. Bottom line, pushers can be fitted for a variety of reasons.

Regarding why no "nudger" was fitted and MCAS adopted instead: A "nudger" would operate on the elevator, not the stab. If the issue is insufficient elevator authority/power to dependably recover from a stall under worst case conditions, nudging the stick will achieve nothing. In such a case, the solution is either more elevator authority (major redesign) for "help the elevator with the stab". The latter seems to be the MCAS solution.
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Old 1st Dec 2018, 16:24
  #1866 (permalink)  
 
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Reuters: Optional warning light could have aided Lion Air engineers before crash

Article discussing which operators do/don't have the optional AOA DISAGREE warning on their NGs and MAXs
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Old 1st Dec 2018, 16:40
  #1867 (permalink)  
 
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Salute Mad!

Stick pushers are sometimes fitted when there are "stability issues approaching the stall" - in such a case, though, in order to fix such issues the pusher needs to be set to trigger BEFORE the adverse characteristics are manifest, with attendant likely adverse impact on stall speeds.
Very good point, and I flew two types with mechanical warnings. One plane had very benign pre-stall characteristics when leading edge flaps were extended as with normal landing configuration. So we had a "shaker". The other had a "pusher" that firmly kicked the stick forward. Subsonic, decent warning, but that sucker had zero warning when supersonic, so the "pusher" was nice.

More from Max:
If the issue is insufficient elevator authority/power to dependably recover from a stall under worst case conditions, nudging the stick will achieve nothing. In such a case, the solution is either more elevator authority (major redesign) for "help the elevator with the stab". The latter seems to be the MCAS solution.
Yep! I am losing a bit of confidence in Big B, although we saw a weak elevator in AF447 that took a long time of full forward stick to move the stab and recover from the stall. At least that's what some of the Pruners here saw in some sim tests.

Gums sends...

Last edited by gums; 1st Dec 2018 at 16:42. Reason: typo/corrrection
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Old 1st Dec 2018, 17:49
  #1868 (permalink)  

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Given other recent events in which the presence/absence of an AOA indicator was significant,
dare I ask why the "AOA disagree" is/was an optional "add-on" for the aircraft instrumentation?

It's not like it meant fitting a new instrument, just a small change in the program code.

Mac
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Old 1st Dec 2018, 18:07
  #1869 (permalink)  
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It's an entire system option Mac: AOA DIsagree is part of the AOA Indication package. Non fliers with spec lists have a long history of boosting their careers with such savings.

Danny and I got together when I was being shouted down that, in the normal world, the B757 had its batteries linked via a relays and cable for total generator loss. 90% plus US forum called Avsig doing the shouting. I supplied a US big three airline senior maintenance man in SFO with the exact drawings from the official Boeing maintenance manual plus the registrations of three US registered aircraft inherited from a failed lease to Australia which had the connected batteries. Two relays, one cable but everything else needed was already fitted on the production line.

In the mid nineties it was still career building to strike even dual position light bulbs off the options list from Boeing. I'm sure you've met these people in medicine.
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Old 1st Dec 2018, 18:12
  #1870 (permalink)  
 
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The pilots had told engineers there had been a disagreement of altitude and airspeed readings based on cockpit alerts, a preliminary report released by Indonesian investigators shows. There was, however, no mention of an AOA disagreement in their write-up, according to the report, and the plane was dispatched on its final flight the next morning from Jakarta.
Not detailed in the manuals, not mentioned in the maintenance history.
Expecting the IAS DISAGREE.
A system which they were not aware of 'in a non normal' environment keeps trimming against their effort to bring the nose up the moment they stop counteracting it.

Very easy post event to identify the trim issue. In that cockpit with a cacophony of aural alerts, warnings, stick shakers that now seem all spurious, identifying the problem quite another.
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Old 1st Dec 2018, 18:27
  #1871 (permalink)  
 
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@Hi_Tech I was wondering as well (#1558).
But, maybe the data only shows a logic output from the computer ... whereas the s/shaker might still be off for some reason? (circuit breaker?)
I am really curious to see data from older flights.
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Old 1st Dec 2018, 18:32
  #1872 (permalink)  
 
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Originally Posted by zzuf View Post
That is not a question I asked.
Stick pushers are only fitted when the actual stall characteristics are non-compliant, not for stability issues approaching the stall. Not heard any issues about the 737 MAX stall characteristics which would mandate fitting a stick pusher.
The 737 can go vertical nose-up at the stall, due to engine thrust/lift moments. As was amply demonstrated at Bournemouth, when a stalling -300 series pitched 44 degrees nose up, as speed continued to reduce to 82 kts. Now that is an adverse stall characteristic, if ever there was one. And remember that the NG and Max have a greater engine thrust/lift nose up moments at the stall, and are much more likely to go vertical.

.

Originally Posted by Mad (Flt) Scientist View Post
.
Regarding why no "nudger" was fitted and MCAS adopted instead: A "nudger" would operate on the elevator, not the stab. If the issue is insufficient elevator authority/power to dependably recover from a stall under worst case conditions, nudging the stick will achieve nothing.
As you said in your preable to this, you set the stick-pusher to operate at a speed when the elevator still has some authority. And you might also limit engine thrust too, to reduce pitch up moments. And the reason you stick-push, rather than trim-push, is so that you are not completely out of trim when you pull out of the ensuing dive.

As you say, a stick-pusher has been used to great and reliable effect on many aircraft types that have similar stabiliser-elevator configuatations to the 737, so why try to re-invent this particular wheel? The stick-push wheel is perfectly circular, while the trim-push system has proven to be hexagonal or octagonal.

.

Originally Posted by patplan View Post
, the BIG ONE- the stick shaker, their failure to mention it, in the log or to the MX, is likely to become one of the major focus for the investigation.
I am left wondering what the new crew knew, before they departed.

There would have been no open ADD-HIL, as the fault was signed off. Did the new crew see the previous tech-log entry, or did they get going in a hurry? Did they fully understand the previous entry, if they even saw it? Did they know this was a recurrent problem, that had happened the previous week? Did the engineer on the flight brief them, or was he just flying out so that there would be maintenance cover at the out-station (ie, was the mechanic asleep down the back...?).

This is speculation, but if the new crew had been fully briefed on all the events of the prievious flight, perhaps they may have handled the situation better. This is the problem with signing off and clearing entries in the tech-log, instead of leaving an open ADD-HIL. Artificially cleared tech-logs keep management and lawyers happy, but are of no use to pilots.

(A clean tech-log does not mean a serviceable aircraft - never has, never will. As this aircraft amply demonstrated. So why not be honest, and keep an ADD-HIL entry open about this fault, so the next crew can read about it...?)

Silver.

Last edited by silverstrata; 1st Dec 2018 at 19:04.
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Old 1st Dec 2018, 19:03
  #1873 (permalink)  
 
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Any aircraft with “underslung” engines could go vertical - it’s up to the pilots to not let that happen.

Pitch power couple
Turbofan aircraft with underslung engines will tend to pitch nose-up as the thrust is increased as the thrust line is below the centre of gravity of the aircraft. Conversely, as power is reduced the aircraft will pitch nose-down.
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Old 1st Dec 2018, 19:21
  #1874 (permalink)  
 
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Originally Posted by ontheklacker View Post
Any aircraft with “underslung” engines could go vertical - it’s up to the pilots to not let that happen.
No, it is not as simple as that. A stick pusher should be required on all aircraft that do not have a natural nose down response, at the stall. And there are many of those. It should not be simply up to the crew to counter a natural pitch-up response, from an aircraft with inadequate stall characteristics.

Look up the BEA (BA) 548 Trident incident at Heathrow, where a lack of a stick-pusher resulted in a disaster. In that case Hawker Sidley (Bae) were forced to add a stick-push system to the Trident, to prevent a repeat event. So the precedent has already been set - should not Boeing also be forced to add a stick-push system, instead of a trim-push system? The trim-push has already shown its flaws, so should not the more trusted stick-push be fitted instead?

Silver
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Old 1st Dec 2018, 19:37
  #1875 (permalink)  
 
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Originally Posted by gums View Post
Salute Mad!
....we saw a weak elevator in AF447 that took a long time of full forward stick to move the stab and recover from the stall. At least that's what some of the Pruners here saw in some sim tests.

Gums sends...
Please could we stop comparisons with AF447. Airbus control system (modified 'C*') is completely different to any Boeing, especially the conventional 737, and the Elevator and Stab effectively act as one (stab following up the elevator when needed). Amazingly the A330 had enough pitch down authority to unstall up to some horrendous A of A, and had the crew only persisted in a nose down demand they might have recovered, though the nose down attitude needed was probably beyond their imagination. Some very courageous AB test pilots tried it out well into post stall (20 degrees or so from memory) and lived to tell the tale.
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Old 1st Dec 2018, 19:37
  #1876 (permalink)  
 
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silverstrata,

I think you will find that a stick pusher was part of the Trident design as early as 1964, some 8 years before the accident in Staines!

https://www.flightglobal.com/FlightP...20-%200246.PDF
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Old 1st Dec 2018, 20:14
  #1877 (permalink)  
 
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Originally Posted by gonebutnotforgotten View Post
Please could we stop comparisons with AF447. Airbus control system (modified 'C*') is completely different to any Boeing, especially the conventional 737, and the Elevator and Stab effectively act as one (stab following up the elevator when needed). Amazingly the A330 had enough pitch down authority to unstall up to some horrendous A of A, and had the crew only persisted in a nose down demand they might have recovered, though the nose down attitude needed was probably beyond their imagination. Some very courageous AB test pilots tried it out well into post stall (20 degrees or so from memory) and lived to tell the tale.
Only one question: Do you thik AF,XL, and Air Asia crews knew where they have stabilizer?
Yes,Boeing and AB are different, but stab in limit positions makes control difficult in both.
Using of manual trim can save day..or maybe not..
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Old 1st Dec 2018, 20:16
  #1878 (permalink)  
 
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Originally Posted by Bergerie1 View Post
silverstrata,

I think you will find that a stick pusher was part of the Trident design as early as 1964, some 8 years before the accident in Staines!
https://www.flightglobal.com/FlightP...20-%200246.PDF
Yes, sorry, my bad. Apparently the fault was recognised in early flight testing back in ‘62, when the Trident entered a flat spin and refused to recover. (See Bartelski, ‘Disasters in the Air’ 2001, and the Flight International page liked above.)

But this shows the scale of the problem. As that very interesting Flight International’ page says, Hawker Sidley (Bae) then had to perform 3,500 stalls on the Trident, with a stick pusher added, before the ARB was satisfied that the new system was reliable. (It would appear that the Trident was the first jet or passenger aircraft with a stick-pusher.). But this report goes on to say:

. Needless to say the system has been engineered (with full duplication) to make sure that if it malfunctions, it cannot create a hazardous situation.
Hmm, so did Boeing do as much testing? And did Boeing do enough to ‘ensure a malfunction would not create a hazardous situation’...?

Silver
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Old 1st Dec 2018, 20:51
  #1879 (permalink)  
 
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Hmm, so did Boeing do as much testing? And did Boeing do enough to ‘ensure a malfunction would not create a hazardous situation’...?
IMHO as a SLF ---- IF as stated in documents --- a single faulty AOA sensor was allowed to repeatedly autotrim stabilizer even after normal disconnect by push/pull on control column- the answer is obvious ..
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Old 1st Dec 2018, 20:53
  #1880 (permalink)  
 
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Originally Posted by silverstrata
Hmm, so did Boeing do as much testing? And did Boeing do enough to ‘ensure a malfunction would not create a hazardous situation’...?
Someone earlier in thread mentioned CFR 25.672 Stability augmentation and automatic and power-operated systems. I think it is worth quoting verbatim, particularly the single failure requirement.
§ 25.672 Stability augmentation and automatic and power-operated systems.
If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with § 25.671 and the following:

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in § 25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system -

(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

(2) The controllability and maneuverability requirements of this part are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and airplane configurations) which is described in the Airplane Flight Manual; and

(3) The trim, stability, and stall characteristics are not impaired below a level needed to permit continued safe flight and landing.
Boeing appears to have kept very quiet about the MCAS for a reason, with barely a reference to it anywhere. Why, would it have jeopardized the grandfathering of type certification?

Last edited by CurtainTwitcher; 1st Dec 2018 at 21:12. Reason: Bolding
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