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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 8th Apr 2019, 21:18
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Originally Posted by infrequentflyer789
Pretty sure it is from the third set of pitot/static sensors, without AOA correction - since there isn't a third AOA sensor.
The question was about using GPS ground speed when there is IAS disagree /UAS.
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Old 8th Apr 2019, 21:40
  #3662 (permalink)  
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Harnesses. I watched the making of the A380 quite recently. Finding some of the harnesses were too short was a jaw-dropping moment.
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Old 8th Apr 2019, 22:05
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GPS speed could be used to have an approximation to real airspeed in case your air data is lost. The error would be huge if you donīt program it carefully (basically wind speed=error). However, if you assume that the readings from air sensors were right to the point in which you had a disagreement, you can calculate the wind at that moment (strictly speaking, an average of the last seconds) and assume a persistent wind vector. The error in the very first moments of "GPS synthesized" airspeed would be negligible, even in a turn. As the aircraft moves and wind conditions change, error will grow, being immense in worst case scenarios and longer times.

Same applies to Inertial speeds.

It could even be possible (maybe some planes do it nowadays, I'm no expert) to compute a real airspeed without air data. At any given moment of the flight, the airspeed is the only unknown parameter of a vector F = m x a, because mass is accurate to some degree from load sheets, acceleration you can measure with the inertial platform and the force is the result of adding the trust of the engine, which is calculated out from engine conditions and tabulated air conditions from GPS altitude, and the lift + drag, which relates to air speed and air conditions with a known characteristic.

In other words, the plane knows its airspeed just by feeling how pitch and thrust translate into acceleration (longitudinal, vertical and lateral) at every moment.

Sure the error will exist (almost every part of the calculation is an estimation), but it would be tolerable (as a backup, say 20 or 30 knots) and it will valid over long periods of time.

This concept of multiple possible ways of calculation of a magnitude is valid with many others (altitude) and to me is one of the things the plane could do before just going all UAS on you.

I dream (it is free) of a dial with a very precise reading when all sensors are working that turns into a less precise reading (a sector instead of a thin needle) when errors are expected, because of alternative calculations. "250 knots with 50 knots error" is a lot better than "250 knots but do not believe it much because another sensor reads different". (And a stick shaker and overspeed clacker on top of it, just to get things interesting).





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Old 8th Apr 2019, 22:06
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We can't see the wood for the trees.
We've got so immersed in MCAS that we're missing the point. Its not MCAS,its the UAS.
This one was just a faulty sensor(not even UAS) Captain's side.They could have engaged AP B,pulled Capt's stick shaker cb,and flown to NBO(no just kiddin).
But thats all it was.....,a failed sensor.
FO gets some disagree flags but his side is good,so is ISFD.And yet the stick shaker and the master caution and the Captain's PFD flags all conspire to make it seem dire.Only the Captain's
shaker was active so they know immediately its not a real stall.
ISFD agrees with FO ASI which agrees with IRS GS....an experienced FO would nudge the skipper@Looks like your side is down,shall I take it?"
We had one poster come on and say he'd climb to MSA and run the Boeing UAS NNC bla bla bla.
This was not UAS.
UAS comes in many forms and can be a nasty scenario on a dark night in IMC.If you're in cruise,I prefer the old Boeing NNC(ie do nothing).
The new NNC is there to cover the possibility you were not in stable flight prior to UAS.After takeoff,you need to make a diagnosis quickly to establish what you're facing....is it single side?is it a
sensor?is it a genuine pitot-static blockage and which one is it,pitot or static....the aeroperu crew had blocked statics so altimeter registered no climb and ASI undereads on climb out.It was night but VMC.If they had climbed to 1500' using radalt as altimeter and IRS GS as speed reference, they would have landed safely after a visual circuit but...you need to have that info and diagnosis in the memory
database.Its not something you can intuit in the moment.
The worst thing they did was climb away from Lima as they lost their altitude reference and their speed reference became less accurate the higher they climbed.
MCAS is the presumed culprit....but MCAS alone didnt bring this aircraft down.Nor the Lionair.It was the crew's inability to diagnose what type of UAS failure they were facing and failure to just simply
fly the plane.If MCAS would activate alone,any crew would simply counter-trim and cut off its electrical supply without much thought. But combine it with a "confusing" UAS scenario and shakers and
warnings and bingo..you get a smoking hole in the ground.
So these UAS scenarios have to be taught in the classroom and sims to all crews so that when the time comes they can make a diagnosis and take the right action.Boeing tell you nothing,they just give you a flight attitude and thrust setting to follow.Pilots have to be trained more on these UAS scenarios before they kill again.
Aeroperu,birgenAF447 and the 2 MAXs,and others.....
Re manual trim...have we had any engineering input as to just when manual trim no longer becomes available in the flight envelope?Is it primarily speed dependent,stabilizer positon-dependent,yoke dependent,or a combination of all 3?
Where is FCENG 84?

Last edited by Rananim; 8th Apr 2019 at 22:29.
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Old 8th Apr 2019, 22:06
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Originally Posted by threemiles
There is a THIRD and independant IAS speed tape on the flight deck, right above the gear announciators.

​​​​GPS delivers ground speed and is of little value, unless you are close to MSL in calm air.
Hi Three Miles. I don't know if you have tried the following but it works ..........

The Standby instruments are basic non corrected airspeed altitude, Horizon and ILS. You an fly a successful approach using just these with all else failed.
An additional value of these third readouts is when you get an disagree between the to main ASI or ALT readouts, the third man can be judge and jury if used carefully.
Indeed that is how you often resolve AIS disagree issues. Which two agree?

Now to Groundspeed GPS. It is a remarkably useful and I would say essential tool in cases of confusion as arose on AF477 and might have been factors in the recent MAX cases. And in many cases total hull loss with loss of airspeed over the years GPS would have got them down safely. You can easily compensate for wind and True Airspeed using simple knowledge of groundspeed at various altitudes.
From cruise altitude right down to touchdown your flight plan has the groundspeed for every leg based on your track, altitude and forecast wind,accurate to within maybe 5 kts. You just fly it using the tables provided by Boeing in the QRH which give pitch and power for every flight condition, weight related. Remember that to crash you have to be wildly out on airspeed. if AF 477 had maintained current GPS speed at time of failure (450 KTS or whatever it was) and not made adjustments to power and pitch, and not got below say 400 kts groundspeed /GPS they could have flown home to Paris, or certainly long enough to work our what was wrong. I have seen demonstrated over the years pilots practice GPS only flying from Altitude to touchdown (on simulators) with no effort whatsoever with NO other data. On 737s during initial type rating training we would put beer mats with blue tack over all the instruments except SBY and GPS and they could fly a perfect circuit even with no ALT readout using GPS and radio altimeter below 2500 feet.
The Tristar taught flying GPS G SPEED approaches in serious headwind landings - none of this is new, but it is being forgotten. So here we have big jets using this technique when it is the very opposite of still air!
Cheers
Y
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Old 8th Apr 2019, 22:11
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Originally Posted by ams6110
And yet Tesla, an automotive company which presumably follows this process, still has an "auto pilot" software function that on more than one occasion drove a car into a stationary object at 70mph.
That is a regulatory failure (or the regulatory process lagging far behind the technology), just like the MCAS issue, neither MCAS or the Tesla autopilot should, IMHO, have the safety rating they do (ander any sane safety analysis) . . . Secondly, the automotive safety standard is nowhere near capable of dealing with this kind of technology . . . it's from the nuts and bolts save lives era . . .

This is not a software problem, the software, certainly in the case of the Boeing product, could have been specified to be compliant with a higher safety case under well established processes, but it wasn't, and so that wasn't the way it was created, that decision would have been made months or years before a single line of code was written. The code monkey writing the code has no input, whatsoever, to that process, single AOA, Dual voted AOA, Triple AOA, inverted AOA on one side, monkey holding the AOA while standing on a unicycle, it's all decided and specified at the system level, miles above the tedium of people writing code.

Tesla (and the automotive industry) actually have a more difficult problem, their autopilot software uses deep learning AI which by its very nature produces indeterministic outputs, so the standard safety approaches and mitigations do not work (indeterminism in a safety critical system is not really allowed), this is another regulatory failure and the safety industry is struggling to understand how to approve these kinds of systems . . . I would not let one drive me.

Fd
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Old 8th Apr 2019, 22:20
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Whatever you might think about Boeing's assumption that a MCAS malfunction could be treated as a species of runaway trim (apart from the fact that this was beyond at least two crews), I wonder if it fully analyzed all implications of a single failure (of an AOA probe).

Unless I'm missing something, if that happened in IMC, the crew would be faced with a stick shaker (on one side), a UAS warning, and a display showing the horizon moving above the flight path. Would they recognize that they had to ignore the first two indications and act immediately on the third? If they refrained from significant control (never mind trim!) inputs until they'd worked through the obvious indication problems, they'd have to deal with a flight path upset on top of everything else.

Perhaps recovering from that situation wouldn't be as challenging as it seems to this SLF. But sure seems a lot tougher than anything the accident crews faced. . .
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Old 8th Apr 2019, 23:43
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Originally Posted by TeachMe
Hello all,

My understanding from these situations is one contributing factor may be that a pilot may ultimately get into a situation where he or she has little to no ability to correct a badly out of trim Max manually or electrically due to aerodynamic loads in certain flight situations. What I have not seen is anyone noting is if this inability, irregardless of how it came about, is the same in other aircraft from Boeing or Airbus. From a 320 to a 380 or a 737 NG or 747 to a 787 would a pilot have the ability to re-trim from the same situation these two flights faced?

TME
737s are fly-by-cable, from the pre-electronics era. 320, 380 and 787s are fly-by-wire, therefore their stabilizers do not have the same limitations

Last edited by deltafox44; 8th Apr 2019 at 23:43. Reason: duplicate
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Old 9th Apr 2019, 01:07
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Originally Posted by Rananim
Only the Captain's shaker was active so they know immediately its not a real stall.
The control columns are connected. I therefore assume that the sticks will both shake (an old 737 800 FCOM I have says "Either stick shaker vibrates both columns through column interconnects"). In the heat of the moment, how could you easily tell which shaker was going off?
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Old 9th Apr 2019, 01:08
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New NY Times Article

Almost all the coverage continues to clobber Boeing. Notably, Tajer is popping up in multiple articles, and providing quotes on the record. Also, more ex-Boeing folks are speaking for attribution, and saying things Boeing won't like.

Boeing’s 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

[Snip]

But the strategy has now left the company in crisis, following two deadly crashes in less than five months. The Max stretched the 737 design, creating a patchwork plane that left pilots without some safety features that could be important in a crisis — ones that have been offered for years on other planes. It is the only modern Boeing jet without an electronic alert system that explains what is malfunctioning and how to resolve it. Instead pilots have to check a manual.

The Max also required makeshift solutions to keep the plane flying like its ancestors, workarounds that may have compromised safety. While the findings aren’t final, investigators suspect that one workaround, an anti-stall system designed to compensate for the larger engines, was central to the crash last month in Ethiopia and an earlier one in Indonesia.

The Max “ain’t your father’s Buick,” said Dennis Tajer, a spokesman for the American Airlines pilots’ union who has flown the 737 for a decade. He added that “it’s not lost on us that the foundation of this aircraft is from the ’60s.”

More

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Old 9th Apr 2019, 01:46
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when things started to really go wrong. Almost no pitch, 340 kts, no ability to pull or trim
The electric trim WAS AVAILABLE to be used.
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Old 9th Apr 2019, 01:55
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Originally Posted by Capn Bloggs
In the heat of the moment, how could you easily tell which shaker was going off?
Look between your legs and see which eccentric motor is spinning.
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Old 9th Apr 2019, 01:59
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Originally Posted by Chu Chu
Unless I'm missing something, if that happened in IMC, the crew would be faced with a stick shaker (on one side), a UAS warning, and a display showing the horizon moving above the flight path. Would they recognize that they had to ignore the first two indications and act immediately on the third? If they refrained from significant control (never mind trim!) inputs until they'd worked through the obvious indication problems, they'd have to deal with a flight path upset on top of everything else.
The proper response would be to turn off the magic, set the attitude and power to a known quantity, fly away from the ground, and then figure out what instruments were lying to you. You know, the basic pilot stuff that is no longer emphasized.
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Old 9th Apr 2019, 04:03
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Originally Posted by gums
Salute!

Thanks, bernd

Guess many were not there for the megathon AF447 discussion about the stall warning relationship to the Aoa when speed was under 60 knots.
On that night, the plane proved it was very stable in a deeply stalled part of the envelope, and had only a slight change in heading versus a violent yaw/roll . So smooth that the crew didn't understand that they had actually stalled - no stall warning audio due to the 60 knot criteria and the "you can't stall this plane" mentality of many at the time.

Gums sends...
Jus' sec here. AF447 had plenty of stall warning. It only stopped after the crew held it into the deep stall. The crew didn't register the warning or believed it spurious.

On the 60 kt criteria, I find it hard to criticize that design decision. It would get increasingly difficult to get reliable meaningful data from the sensors at that point (i.e. IAS vs CAS spread). And who would have thought an airliner would actually manage to be flown to that point.

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Old 9th Apr 2019, 04:29
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Originally Posted by yanrair
The Tristar taught flying GPS G SPEED approaches in serious headwind landings - none of this is new, but it is being forgotten. So here we have big jets using this technique when it is the very opposite of still air!
Surely the Tristar predated GPS by some years.
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Old 9th Apr 2019, 04:58
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Originally Posted by Icarus2001


The electric trim WAS AVAILABLE to be used.
It was cut out by the cutout switches.
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Old 9th Apr 2019, 05:05
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Reading this whole thread, this civilian would have no problem flying on a MAX with any competent pilot at any major carrier, at this point, if it could be proved that the MCAS implementation is the only major change/problem not previously disclosed with the design of the MAX.

What else lurks in the dark of undisclosed changes? What other switches have had their independent control effectively coupled together, with no disclosure in the training deck?

At least one unspecified software bug regarding control surfaces exists and is being addressed in secret, at least so far.

I'm no longer too concerned with the ins and outs of MCAS, it's failures and fixes. It could be perfectly repaired, and I still will never set foot on a MAX, not because of MCAS or its underlying performance change that it corrects, but because of the arrogance that led to it in the first place. Without a complete, independent analysis of all the cascading impacts of all the other design changes, by an impartial 3rd party, given access to all the internal documentation and communication that went into the MAX, no one can convince me, definitively, that it is actually safe to fly. You still can't prove the non-existence of something unknown.

If they could bury a change as critical as this, and remove, (or never allow) the ability to shut it off, they could bury anything to cover up critical design changes.

Was the wing re-designed to deal with the increased thrust from the new engines? Really, every last bit of it, with no influence from the directive to not trigger a new type rating? Or was the new engine just scabbed onto the old structure, with local reinforcement? How do you know?

Up intil 6 months ago, I would assume Boeing modeled the harmonic changes to the wing structure in the most rigorous process of any engineering undertaking ever executed. Now, I have doubts. If they were beefing up the wing for more thrust, why couldn't they roll in an entirely new wing design to accommodate longer landing gear, and keep the engines back where they belonged? New type rating trigger?

Fixing MCAS is not the problem. The culture that led to it is.
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Old 9th Apr 2019, 05:15
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Originally Posted by ecto1
GPS speed could be used to have an approximation to real airspeed in case your air data is lost. The error would be huge if you donīt program it carefully (basically wind speed=error). However, if you assume that the readings from air sensors were right to the point in which you had a disagreement, you can calculate the wind at that moment (strictly speaking, an average of the last seconds) and assume a persistent wind vector. The error in the very first moments of "GPS synthesized" airspeed would be negligible, even in a turn. As the aircraft moves and wind conditions change, error will grow, being immense in worst case scenarios and longer times.

Same applies to Inertial speeds.

It could even be possible (maybe some planes do it nowadays, I'm no expert) to compute a real airspeed without air data. At any given moment of the flight, the airspeed is the only unknown parameter of a vector F = m x a, because mass is accurate to some degree from load sheets, acceleration you can measure with the inertial platform and the force is the result of adding the trust of the engine, which is calculated out from engine conditions and tabulated air conditions from GPS altitude, and the lift + drag, which relates to air speed and air conditions with a known characteristic.

In other words, the plane knows its airspeed just by feeling how pitch and thrust translate into acceleration (longitudinal, vertical and lateral) at every moment.

Sure the error will exist (almost every part of the calculation is an estimation), but it would be tolerable (as a backup, say 20 or 30 knots) and it will valid over long periods of time.

This concept of multiple possible ways of calculation of a magnitude is valid with many others (altitude) and to me is one of the things the plane could do before just going all UAS on you.

I dream (it is free) of a dial with a very precise reading when all sensors are working that turns into a less precise reading (a sector instead of a thin needle) when errors are expected, because of alternative calculations. "250 knots with 50 knots error" is a lot better than "250 knots but do not believe it much because another sensor reads different". (And a stick shaker and overspeed clacker on top of it, just to get things interesting).
There is not just another sensor, there are two other sensors. One is called ISFD speed tape that can be used to vote 2 over 1.

If two or three probes are iced and all three tapes show different speed GPS ground speed may be helpful to understand, e.g. a deep stall, by a matter of magnitude. 0 kts GS is certainly not a comfortable number then. But that is a different discussion. This thread is about IAS disagree and stick shaker upon lift off.
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Old 9th Apr 2019, 05:19
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Originally Posted by threemiles
It was cut out by the cutout switches.
Well, it was cut out by the pilots. They had the option to re-trim the aircraft using electric trim before hitting the cutout. I believe this "option" occurred to the crew close to the end when they re-enabled the electric trim but their attempts to re-trim with the column switches was unsuccessful (either through pilot error or malfunction). Had they done this earlier, right before they activated the STAB TRIM CUTOUT, they would have been in a very similar situation to the pre-accident LionAir flight -- a trimmed, stable aircraft, with AP disconnected, and stick shaker going off on PF side.

A couple of points, one made a few posts back.

Firstly, it seems the lessons from the pre-accident LionAir flight and the subsequent accident flight were not learned well enough. As far as we know, the MCAS issue that occurs as a result of PF-side erroneous AoA signal is completely survivable by the crew taking the correct course of action. It seems that the correct course of action wasn't spelled out clearly enough for the ET302 crew, or it was not drummed into them methodically enough. That's a further failing of the airline industry following the initial accident.

Secondly, it has been remarked here on numerous occasions that it is extremely rare for a transport crew to encounter a stick shaker alert. Had the pre-accident LionAir B737 been grounded following that flight, and had the ET302 crew leveled the aircraft before disabling the electric trim and subsequently managed to land, that would have been two flights with PF-side stick shaker active for the duration of those flights. That would suggest a systemic issue, but it does not appear to have received the same attention as the MCAS response.
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Old 9th Apr 2019, 05:23
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Originally Posted by weemonkey
Hmm. So a direct reading gauge with nothing getting in the way.

Apart from the cabin diff press indicator tap.

So not totally independent after all...
Cabin diff press indicator has no influence on ISFD IAS shown.
Some sophisticated numerical compensations that are done inside ADM and ADIRU are missing, as for AoA. But these are not too relevant for normal manoeuvering. All non digital airplanes have flown well like this for decades.​

Last edited by threemiles; 9th Apr 2019 at 05:34.
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