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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 13th Apr 2019, 08:09
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VicMel, an interesting analysis #3958. Together with that of Smythe … now confused.

(If) Vane-sensed AoA requires correction; is this correction in the vane unit or elsewhere. Peter Lemme argues that errors originate from the vane unit as AoA output is ‘sent’ and used by many separate boxes.
Alternatively a separate (remote) calculation would be more logical with the need of other factors, e.g. embedded in ADC for Mach; which box (function) is not so important if the corrected AoA is available on a digital bus to all other computational boxes. This would also negate the view of a vane-origin error.

Airspeed pressure-error corrections depend on the corrected AoA; differences between ADC computations are alerted (Speed, Alt, Disagree). This should not change the AoA.

AoA is use to position the low speed awareness symbol on the airspeed scale, but this too uses output AoA, it should not correct - change either AoA or airspeed.

Thus what correction is being discussed; where is the computation done, and how is the output accessed by many other functions requiring AoA - MCAS one amongst many.

Re vane damping; an earlier suggestion was that the vane slipped position on the shaft; fortuitously catching at different times and values in each accident. A slipping vane/shaft, when snagged would then act as a single unit involving aerodynamic and mass damping - but incorrect AoA.
Although unlikely, Occam might like the simple mechanical approach.

Alternatively, the digital views might follow Moore-Murphy, where with increasing complexity and add-ons, there is even greater risk of error, the need crosschecking and multiple sources would be paramount. Somewhat lacking in this system.




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Old 13th Apr 2019, 08:33
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Originally Posted by Capn Bloggs
ex-USAF Major General. Says it all. Blame the pilots when in reality they were flying a deathtrap. What are we, testpilots, finely honed, ready to pounce into action when disaster strikes?
Seekingalpha is an investment-related blog, anybody can write whatever they like there. There are two kinds of people on that site: those talking up stock they own, and those talking down stock they sold short. Utterly unreliable as a source of investment info, let alone anything else.
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Old 13th Apr 2019, 08:44
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Delarue, the thing that annoys me is he sounds credible, and that the riff raff probably believe him.
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Old 13th Apr 2019, 08:52
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Auto Throttle

At one point the FO selected 238kts in the speed window.
I think that was the only time I can see they try to control speed. and a good speed indeed.
My goto speed is 230kts non the 737-800 at this stage as this gives me any options and safe margins.
BUT
The AT must have disconnected at one point as the IAS became different.
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Old 13th Apr 2019, 09:09
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Originally Posted by BluSdUp
The AT must have disconnected at one point as the IAS became different.
They probably had the AT disconnect annunciator flashing away until the end.

When I see that AT disconnect flashing for more than a few seconds, I know the person I am sitting next to is overloaded and has lost SA. It's interesting experiment to see how long before they attend to it, it can be quite some time. Occasionally they won't even notice I've reached up and pushed the annunciator to cancel it.
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Old 13th Apr 2019, 10:45
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CurtainTwitcher;"They probably had the AT disconnect annunciator flashing away until the end."

"When I see that AT disconnect flashing for more than a few seconds, I know the person I am sitting next to is overloaded and has lost SA. It's interesting experiment to see how long before they attend to it, it can be quite some time. Occasionally they won't even notice I've reached up and pushed the annunciator to cancel it."

...Except that it's hard not to hear the annoying clacker horn as they zoomed past 340 kts (VMO) 3 minutes after lift off, and past 458 kts two minutes after that. It's apparent that these guys were totally engrossed with pitch control ignoring also the increasing noise of rushing air from the slipstream, ignoring also in day VMC at low altitude the fast moving terrain below their feet.

...
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Old 13th Apr 2019, 11:52
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Originally Posted by Smythe
The best solution would be to mount the AoA vane on the wing at midspan, but the disruption from the engine, and moving leading edge prevents this.
No, the wing would be the worst place to measure AoA, since airflow perturbation is the highest there. The only place to get an good AoA is on a long stick ahead of the nose. Even there it would be correct only in steady flight in still air...

Last edited by deltafox44; 13th Apr 2019 at 12:07.
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Old 13th Apr 2019, 13:28
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Originally Posted by L39 Guy
Based upon my 36 years/26,000 hours of flying, provided that one does not "jerk" the aircraft into the air, if one rotates the aircraft nose at a normal rate to the take-off attitude, roughly 15 degrees in the B737 at 3 degrees per second, the aircraft go flying when the wings are ready to let it go flying, i.e. when the have created enough lift. And, with both engines running, the aircraft will accelerate. Because of this characteristic, this will cover up a lot of mistakes such as wrong flap setting, wrong power setting, wrong C of G (although that would be more an issue of control column forces to rotate as the stab trim setting is based upon the C of G). This would mean the aircraft would take more runway if heavier, lower flaps setting (1 instead of 5 for example), lower power setting and less runway with the opposite conditions.

Regardless of any of this, surely by 400 ft there would be communication between the two pilots about the indicated airspeed between the three airspeed indicators in the flight deck, particularly since the Captain was an 8000+ hour pilot; the FO was probably shell shocked.

But either way - unreliable airspeed or a bona fide stall - why on earth would the Captain call "Command", i.e autopilot engagement at 400 ft? You do not engage an autopilot when one is in a stall, you do not engage an autopilot with an unreliable airspeed.

To me, this points to an experience, training and attitude problem the world over in modern airline flying. Pilots no longer have the basic flying skills to fly an airplane anymore without autopilot, autothrottle, flight director and, heavens forbid, GPS/RNAV! Where I fly (Canada) we call these people "Children of the Magenta Line". I don't know if other countries use this term or not but what it means is all they know is how to fly the magenta line on the nav display as well as the magenta pointers on the primary flight display.

I know in other parts of the world, hand flying an aircraft is not only discouraged its against SOP's and is subject to the "FDR Police". It's all fine and dandy when things are going well but when the crap hits the fan and one actually has to revert to basic flying skills they are not there, either because they never were there in the first place or, if they were, they have atrophied because they haven't been used in years.

While the MAX incident/accidents have brought this home tragically - trying to use the autopilot in a unreliable airspeed situation or a true stall (take your pick), being unable to trim the aircraft with the electric trim (continuous trim rather than short bursts), being unable to manually trim and fly the aircraft, being unable to manage the airspeed and not going the speed of heat, or questionable airmanship decisions such as continuing to destination with unreliable airspeed, and so on - there have been scores of incidents such as the Korean 777 in SFO wherein the crew could not fly a visual approach on a clear day, etc. Only by pure luck or the incredible survivability of the aircraft that no one was killed in the crash itself. And there are scores of other examples of incidents that could have easily become fatal accidents, just go to avherald.com to see for yourself.

The entire industry - ICAO, IATA, the individual airlines, the individual CAA's, the pilot unions, aircraft manufacturers, etc - need to do some serious navel gazing to get the level of pilot proficiency and training back to the point where paying customers can count on the pilot to be the last line of defense when the unexpected happens such as a double engine failure (US Air). Technology is great but it has its limitations and at the end of the day, trained and competent pilots are still needed when the unanticipated events happen.

Editorial over.
They even tried to engage the autopilot near the end at 05:43:15, hoping the automation would fix their problems!
It seems the reason they switched the cutoff-switches back was so they could reengange the autopilot.

This is certainly a severe case of "the children of the magenta line".

Last edited by Brosa; 13th Apr 2019 at 16:56.
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Old 13th Apr 2019, 14:34
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It is some while ago I had to handle the airfoil basics but I think that upwash field is affected by speed and fuselage angle of attac affect the side mounted vane. So both speed and fuselage AoA may have an effect that might be taken into account when correcting the vane reading.
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Old 13th Apr 2019, 14:55
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Originally Posted by MurphyWasRight
That exchange was at/after the electrical trim was re-enabled, I believe the 'manual' refers to electrical trim switches.
Disagree. From the report:

At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
From the FDR traces, no electric trim command (autopilot or manual) is recorded between approx 05:41 and 05:43, therefore the above exchange can only be referring to manual trim with the wheel (unless you are suggesting a simultaneous failure of the trim switches).
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Old 13th Apr 2019, 15:43
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Originally Posted by infrequentflyer789
Originally Posted by MurphyWasRight
That exchange was at/after the electrical trim was re-enabled, I believe the 'manual' refers to electrical trim switches.
Disagree. From the report:
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
From the FDR traces, no electric trim command (autopilot or manual) is recorded between approx 05:41 and 05:43, therefore the above exchange can only be referring to manual trim with the wheel (unless you are suggesting a simultaneous failure of the trim switches).
You are correct, I did not cross check the times correctly.

This could be explained by the pilot thinking that the cutout switches worked as on the 737NG where it is possible to disable automatic trim inputs using one cutout switch while preserving pilot electicall trim control. This changed on the MAX, either switch disables all electrical trim, no idea why that change was made.

The training slide I saw stated the names had changed but I don't recall seeing a statement on the changed functionality, anyone who has access to the conversion slides please clarify if you can,

From a functional schematic posted on another thread it is likely that this would have disabled the trim switches in a way that they would not show on the FDR, unlike the MCAS attempt at ~ 5:40:45 which did not affect the trim.

This might be part of the answer to 'what were they doing all that time', (mashing on disabled trim switches) while the speed to got even higher before attempting (mechanical) manual trim.
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Old 13th Apr 2019, 16:41
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Originally Posted by Brosa
They even tried to engage the autopilot near the end at 05:43:15, hoping the automation would fix their problems!
It seems the reason they switched the cutoff-switches back was so they could reengange the autopilot.

This is certainly a severe caser of "the children of the magenta line".
The children of the magenta line are playing a video game. They are not flying.
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Old 13th Apr 2019, 17:30
  #3933 (permalink)  
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https://www.nytimes.com/interactive/...h-cockpit.html
HomeWhat the Lion Air Pilots May Have Needed to Do to Avoid a CrashBy JAMES GLANZ, MIKA GRÖNDAHL, ALLISON MCCANN and JEREMY WHITE NOV. 16, 2018

1. Control stabilizer in tail

wing with electric switch

3. Turn wheel

to manually

control stabilizer

2. Shut down

electricity to

stabilizer controls


By The New York Times. Photograph by Vedant Agarwal.New data from the Lion Air flight shows a fatal tug-of-war between man and machine after the plane’s nose was repeatedly forced down, apparently by the automatic system described below.



Investigators and experts are uncertain why Lion Air Flight 610 plummeted into the Java Sea last month, killing all 189 people on board. But they are focusing on an automatic system designed to keep the plane, a Boeing 737 Max 8, from going into a “stall” condition.

A stall can occur when the plane’s nose points upward at too great an angle, robbing the craft of the aerodynamic lift that allows it to stay aloft. But if the 737 receives incorrect data on the angle – as the same plane did on the flight just before the crash – the system designed to save the plane can instead force the nose down, potentially sending it into a fatal dive.

The situation in this case is further complicated by Boeing’s installation of the system, which the company did without explaining it in the new model’s operating manual. So the pilots might well have been unfamiliar with it.

In a statement, Boeing said it was confident in the safety of the Boeing 737 Max, and added, “While we can’t discuss specifics of an on-going investigation, we have provided two updates to operators that re-emphasize existing operating procedures — the series of steps required — for these situations.”

If the pilots of Lion Air 610 did in fact confront an emergency with this type of anti-stall system, they would have had to take a rapid series of complex steps to understand what was happening and keep the jetliner flying properly. These steps were not in the manual, and the pilots had not been trained in them.

Approximate data on the plane’s speed and altitude on the 11 minutes it spent in the air suggest that the first indication of trouble may have come just above 2,000 feet, when its trajectory was beginning to level off.



The 11-minute

climb and descent

of Lion Air Flight 610

3,000 feet

Possible first indication

of trouble

1,000 feet

6:21 a.m.

6:22

6:23

6:24

6:25

6:26

6:27

6:28

6:29

6:30

6:31 a.m.


The New York Times | Source: Flightradar24At that point, said John Cox, the former executive chairman of the Air Line Pilots Association and now a safety consultant, something unexpected occurred: instead of leveling off momentarily, the plane’s altitude dropped around 600 feet. “This may have been the onset, the first time something happened,” Mr. Cox said.

By this point in the flight, the pilots typically would have moved the flaps on the main wings from the down position needed for takeoff into a trimmed up position for flying at higher speeds. The Boeing anti-stall system cannot activate until the flaps are up.

After the 600-foot drop, the pilots climbed to 5,000 feet, possibly to give themselves more maneuvering room if another unexpected dive occurred. They sought and received permission to return to the airport, but for reasons not yet known, they did not appear to have tried to do so. When the plane leveled off just above 5,000 feet, there was another indication that something was amiss: instead of the smooth, straight flight that the usual autopilot setting would produce, the plane pitched up and down, indicating manual operation.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
Altitude of

Lion Air Flight 610

3,000 feet

Pilot appears to

struggle with

manual control

1,000 feet

6:21 a.m.

6:22

6:23

6:24

6:25

6:26

6:27

6:28

6:29

6:30

6:31 a.m.


The New York Times | Source: Flightradar24That could indicate that the pilot simply was not very good at flying in manual mode. More likely, said Les Westbrooks, an associate professor at Embry Riddle Aeronautical University, the pilot already was struggling with some system causing the plane to veer from its straight path.

In that case, Mr. Westbrooks said, it would be like trying to drive a car that is tugging one way or another – the driver can counteract it, but the path is jagged. The plane’s up-and-down motion continued, including a larger dip and recovery of about 1,000 feet in the last few minutes of the flight that might have felt like a bit of rough turbulence to passengers, said R. John Hansman Jr., a professor of aeronautics and astronautics and director of the international center for air transportation at the Massachusetts Institute of Technology.

Then, suddenly, the plane went down.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
Altitude of

Lion Air Flight 610

Plane

plummets

3,000 feet

1,000 feet

6:21 a.m.

6:22

6:23

6:24

6:25

6:26

6:27

6:28

6:29

6:30

6:31 a.m.


The New York Times | Source: Flightradar24There has been no official finding that the anti-stall system – known as the maneuvering characteristics augmentation system, or M.C.A.S. – was activated. But if the 737’s sensors were indicating erroneously that the nose had pitched dangerously up, the pilot’s first warning might have been a “stick shaker:” the yoke – the steering wheel-like handles in front of the pilot and co-pilot – would vibrate.

If the false warning in turn activated the automatic anti-stall system, the pilots would have had to take a series of rapid and not necessarily intuitive steps to maintain control – a particular challenge since those steps were not in the plane’s operating manual and the pilots had not been trained on how to respond.

If it sensed a stall, the system would have automatically pushed up the forward edge of the stabilizers, the larger of the horizontal surfaces on the plane’s tail section, in order to put downward pressure on the nose.

To counter the nose-down movement, the pilot’s natural reaction would probably have been to use his yoke, which moves the other, smaller surfaces on the plane’s tail, the elevators. But trying that maneuver might well have wasted precious time without solving the problem because the downward force on the nose exerted by the stabilizer is greater than the opposite force the pilot would be trying to exert through the elevator, said Pat Anderson, a professor of aerospace engineering at Embry Riddle.

“After a period of time, the elevator is going to lose, and the stabilizer is going to win,” he said.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
The M.C.A.S system angles the

stabilizer, pushing the tail up.

As a result, the

nose goes down.

ELEVATOR

HORIZONTAL STABILIZER


The New York TimesWith only fragmentary data available, Mr. Hansman said he suspects that a runaway of the M.C.A.S. system played a central role in the crash. “The system basically overrode the pilot in that situation,” Mr. Hansman said.

If the anti-stall system indeed ran away with the stabilizer control, only a fast sequence of steps by the pilot and first officer could have saved the aircraft, instructions later issued by Boeing show.

On the outside of the yoke in front of both the pilot and the first officer, there is a switch for electrically controlling the trim – the angle of the stabilizers. If the pilot understood what was happening, he could have used that switch for a few seconds at a time to counteract what the M.C.A.S. was doing to the stabilizers. But that would have been only a temporary solution: the pilot has to release the switch or the nose could go too high. But if he releases the switch, the anti-stall system would reactivate a few seconds later, according to a bulletin issued by Boeing.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
ELECTRIC

STABILIZER

TRIM SWITCH

YOKE

1. Use thumb on this

switch to temporarily

counteract the automatic

stabilizer movement.


The New York TimesThe crucial step, according to the Boeing bulletin, would be to reach across to the central console to a pair of switches (sometimes protected with covers that must be opened), and flip the switches off. Those switches disable electric control of the motor that moves the stabilizers up and down, preventing the anti-stall system from exerting control over their position.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
STABILIZER

TRIM CUTOUT

2. Flip the covers down

and hit the switches

to cut off electrical

power to stabilizers.


The New York TimesThe final step would complete the process for giving the pilots physical control. Cables for manually operating the stabilizers run over a wheel – actually two wheels, one on either side of the console next to the ankles of the pilot and first officer. One of the pilots must rotate the wheel to pull the stabilizer back into the correct position.


[img]data:image/gif;base64,R0lGODlhCgAKAIAAAB8fHwAAACH5BAEAAAAALAAAAAAKAAoAA AIIhI+py+0PYysAOw==[/img]
STABILIZER

TRIM WHEEL

3. Take manual

control of stabilizers

by cranking this wheel.


The New York TimesDesigned and produced by Umi Syam. Hannah Beech contributed reporting.

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Old 13th Apr 2019, 17:34
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https://leehamnews.com/2019/04/05/bj...irst-analysis/

Bjorn’s Corner: ET302 crash report, the first analysis

April 05, 2019, ©. Leeham News: The preliminary accident report of the ET302 crash was released yesterday. It confirmed what we wrote about earlier in the week, the pilots followed the prescribed procedure to stop MCAS. Yet they didn’t make it.

Part of why we presented Wednesday. Here follows additional analysis after studying the information in the Preliminary Crash Report.

https://leehamnews.com/wp-content/up...eral-trace.png
Figure 1. The general Flight Data Recorder trace from ET302. Source: ET302 preliminary report.
The report confirmed our assumptions
The report released by the Ethiopian Ministry of Transport is a preliminary report. It follows the structure of the Lion Air JT610 preliminary report.

It confirms what we wrote about earlier in the week, the Flight Crew followed the procedures prescribed by FAA and Boeing in AD 2018-23-51. And as predicted the Flight Crew could not trim manually, the trim wheel can’t be moved at the speeds ET302 flew.

The traces from the report is Shown in Figure 1 and 2 (click on them to make them larger).

Figure 1 shows the general Flight Information traces whereas Figure 2 shows the specific information around MCAS and the signals which affect MCAS.

https://leehamnews.com/wp-content/up...-specifics.png
Figure 2. The Flight Data Recorder trace from ET302 which deals with MCAS related data. Source: ET302 preliminary report.

etcetera
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Old 13th Apr 2019, 20:32
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Originally Posted by deltafox44
I don't know if AoA value shown on the graph was value from the vane or value corrected by algorithms. I suppose both are recorded. Anyway, pitch rate correction cannot drive corrected value from +75° to -60° !
Back in the days when I was working on A320 software we were restricted on how much we could send to the FDR. We would have loved to send raw data as well as processed data for a parameter, it would have helped enormously with post flight diagnostics. So I am fairly certain the value on the FDR is the fully processed value that the ADIRU puts on the ARINC 429 bus for the FCC (and whatever else) to use in their own processing.The value can go from +75 to -60deg because (I believe) the 6 stage AoA correction computation (Pitch Rate possibly being the main one) is using garbage parameters and so producing a garbage output. I think the large negative Pitch Rate starting at 05:43:24 may have caused a change to which garbage parameter was picked up. However although the L AoA value is now dynamic, i.e. not stuck, it does not get anywhere near to being correct as it does not track the R AoA in the precise way that it did at the beginning of the flight.
Originally Posted by safetypee
Thus what correction is being discussed; where is the computation done, and how is the output accessed by many other functions requiring AoA - MCAS one amongst many.
There are a number of conditioning/corrections going on. Starting with the description in #2857, the AoA sensor provides analogue voltages representing the Sine & Cosine of the shaft angle, with no corrections. The (simple) AoA sensor does not have access to the other parameters needed to do any more than provide raw measurements. These 2 analogue signals go to the ADIRU (and possibly to the SMYD); the ADIRU takes these signals into its A-To-D front end to turn into digital values, which are then made available to the ADIRU software. The software *should* then do a sine**2 + cosine**2 = 1 check; if that passes then it should calculate RawAoA as Atan (Sin(ShaftAngle) / Cos(ShaftAngle)) *checking* that Cos(ShaftAngle) is not so near 0 that an overflow would occur (see crash of first launch of Ariane 5 if you don’t!). The software *should* then check that RawAoA is within +/- valid limits and *should* check the rate of change from the last reading as plausible. A cross check on any other AoA *should/must* be done. Then the AoA *should* be smoothed to remove electrical or vibration noise. Now the 6 corrections (Pitch Rate, Mach No, etc) can be applied. Finally the WingAoA can be put out onto the ARINC 429 bus, as a fully validated, ready to use value for whoever needs it such as cockpit displays, FCC and possibly SMYD.
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Old 13th Apr 2019, 21:14
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Originally Posted by VicMel;10446915[size=3
The value can go from +75 to -60deg because (I believe) the 6 stage AoA correction computation (Pitch Rate possibly being the main one) is using garbage parameters and so producing a garbage output. I think the large negative Pitch Rate starting at 05:43:24 may have caused a change to which garbage parameter was picked up. However although the L AoA value is now dynamic, i.e. not stuck, it does not get anywhere near to being correct as it does not track the R AoA in the precise way that it did at the beginning of the flight.
Vic
While I agree that some SW issue may have been involved with Lion Air (wrong side detect pin?) I cannot see why anything beyond detachment of the AoA vane is needed to explain the rapid swing to ~70 with later almost perfect tracking of G forces of ~+0.5G to ~ -2.0G between 05:43:25 and end of recording.

The bird strike or pre existing damage that let go at takeoff also explains the AoA heater fail.

Last edited by MurphyWasRight; 13th Apr 2019 at 21:16. Reason: Fixed plus sign location.
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Old 13th Apr 2019, 21:22
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VicMel, thanks,
With that info and previous analysis, how might the correction routine ‘reset’, if it did, between flights?
How or why would this corruption occur on the particular accident flights apparently at random, or reoccur after the first Lion incident; conversely why were there not more instances of inaccurate AoA.
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Old 13th Apr 2019, 22:58
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Curious number of new posters piling it up on the pilots of the flight in question, all the while drawing attention away from the true culprits (Boeing & Co). PR at work?
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Old 13th Apr 2019, 23:38
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Well brak, that may be true, but countered by the very strongly worded post above. It hits firmly at Boeing, and it's hard to not agree with the fundamental points.
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Old 13th Apr 2019, 23:43
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Originally Posted by brak
Curious number of new posters piling it up on the pilots of the flight in question, all the while drawing attention away from the true culprits (Boeing & Co). PR at work?
No, it is not Boeing PR. As more information becomes available, and there is more understanding of what actually happened, those of us who actually get paid to fly can see that these pilots made a lot of mistakes.

The ET302 pilots did not follow the proper procedures after takeoff when they were faced with an Angle Of Attack disagreement during a day VFR departure. Boeing has taken steps to make the B737 MAX MCAS safer (foolproof?), but there will always be pilots who are their own worst enemies.
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