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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 12th Apr 2019, 13:16
  #3901 (permalink)  
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VicMel Thought provoking.

I find it hard to believe that a counter weight (without a vane) would stay exactly on 74.5 for minutes and not now be affected by vibration plus all of the other changes to flight dynamics. A fixed offset, sometimes tracking the R AoA value, sometimes not, looks to me like a software generated value.
I'm swinging between both extremes of scenario. However, that balance weight flopping near the end of ET's flight is hard to reconcile, even with Vic's logic.

That slight change of AoA at 05:41:22 - ish, is also troubling me. Why there? Why so consistent before and then after the change? i.e., if it can change at all, why would it remain steady either side of the change?
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Old 12th Apr 2019, 13:19
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Originally Posted by VicMel View Post
I agree that loss of a vane is questionable for 2 reasons:-
1) The idea that there are 2 (or 3) different AoA sensor faults were experienced on the 2 Lion Air flights and ET302 flight seems to me to be very unlikely from a probabilistic point of view, especially so as the AoA sensor is apparently generally very reliable.

I think the “lost vane” idea came from an observation on ET 302’s FDR Data chart that Vertical Acceleration lines up with a jump in AoA. It is possible that “cause and effect” may have been misinterpreted here because Vertical Acceleration is a consequence of, and directly related to Pitch Rate. This would fit in with the fact that AoA L was disrupted on the 2 Lion Air flights (as well as on ET 302) just around take off when there would have been a large value for pitch rate.
Well, how does that align with ALL the information?
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.
At 05:38:43 and about 50 ft radio altitude, the flight director roll mode changed to LNAV.
At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state.

There is very little in terms of cause and effect that would satisfy the heater parameter change other than losing the vane itself. (Unless you want to believe this is entirely spurious).

- GY

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Old 12th Apr 2019, 13:27
  #3903 (permalink)  
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Originally Posted by CurtainTwitcher View Post
One has to wonder if the Boeing PR machine is starting to kick into gear behind the scenes, and orchestrate a smear campaign through friendlies to point the finger at the pilots (as per the Seeking Alpha The Boeing 737 MAX 8 Crashes: The Case For Pilot Error) and operators instead of Boeing. Boeing Has Called 737 Max 8 ‘Not Suitable’ for Certain Airports. The "Not suitable for certain airports" implies Jakarta as being in this category (too hot). All the hallmarks, unattributed expert opinions such as "Mark". Reporters just happened to find these U.S. International Trade Commission documents lying around?
In reference to the "Not Suitable" article statement... What a load of nonsense.

How does an AOA sensor become discombobulated by temp or pressure altitude???? Seriously, has relaxing the pot laws in WA resulted in loopiness in Chicago head office? If Boeing wants to defend their position, they need to get serious and deal with the facts at hand and not puff smoke or play with mirrors.

WAT limits per 25 Subpart B control suitability of the aircraft for a particular operation for the certification of the aircraft, not the name or number written on the side of the plane by the OEM.
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Old 12th Apr 2019, 14:00
  #3904 (permalink)  
 
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Totally agree that this is an effort to build the public opinion case for pilot error.
To me the worst part of the 'case for pilot error' is no mention of even the possibility that the crew was unable to manually trim and the suggestion they were very slowly winding the wrong way.
The slight .2 unit wrong way trim during the manual trim phase of the flight could be due either to struggles with the wheel or (less likely in imho) back drive from the extreme load.

He then slams them for the aparent last ditch re-enabling of electric trim.

The lack of speed management certainly was a factor but had they been able to manually trim they would likely dealt with it next.
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Old 12th Apr 2019, 14:17
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I think there is another HF issue (already commented on some time back) in that it is utterly counter-intuitive to reduce thrust when the nose is pitching down. It is like leaning to right when you want to turn your bicycle to the left.
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Old 12th Apr 2019, 14:18
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Originally Posted by MurphyWasRight View Post
Totally agree that this is an effort to build the public opinion case for pilot error.
I find it quite remarkable that it takes such a long windup to finally conclude that the crew did not do everything perfectly. Duh. No human ever does.

And then it just stops. What is the point of finger-pointing? How can that help anyone in any way? (Except perhaps Boeing's reputation, but even that is doubtful.)

A finding of "Human Error", can never be the end of an analysis, rather it must be the start of asking questions such as:
  • What was the exact situation the operators were in?
  • What was the information they could get?
  • Was some information maybe ambiguous? Even contradictory? Hard to find?
  • How much time did they have to find it?
  • How much time did they have to analyse it?
  • Were they trained to evaluate the information properly?
  • Were there perhaps multiple anomalies requiring different, possibly even contradictory procedures?
  • Was there perhaps cognitive overload?
  • Did they (could they?) have an understanding of why the system did what it did?
  • What additional information do we have now, that the operators at the time did not have? (The easy one: we know that what they did eventually led to an unrecoverable situation. They didn't. Or else they wouldn't have done it.)
  • Which again leads to: why did they do what they did?
  • How can we prevent:
    • ... crews from doing the same things again, or better still:
    • ... anyone from getting into the situation in the first place?
I repeat here the image I posted way back that makes these ideas very clear:


From The Field Guide to Understanding 'Human Error' by Sidney Dekker

Bernd
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Old 12th Apr 2019, 15:11
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I used to always think that we, as a community, tend to focus more on the who, instead of the more pertinent, what, which should be followed by the even more pertinent, why. I now understand that the whole industry is afflicted by the malaise.
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Old 12th Apr 2019, 15:35
  #3908 (permalink)  
 
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in that it is utterly counter-intuitive to reduce thrust when the nose is pitching down.
Have you done jet upset or UA recovery in the sim? Low nose is always reduce power.
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Old 12th Apr 2019, 16:29
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Originally Posted by Loose rivets View Post
VicMel Thought provoking.



I'm swinging between both extremes of scenario. However, that balance weight flopping near the end of ET's flight is hard to reconcile, even with Vic's logic.

That slight change of AoA at 05:41:22 - ish, is also troubling me. Why there? Why so consistent before and then after the change? i.e., if it can change at all, why would it remain steady either side of the change?
Given the oil damping system and inherent friction it would be reasonable to expect the weight to stay put and not respond to vibration or minor changes in g.
.
The forces on an operating AoA vane/system would be high compared to the weight which is just there to balance the vane.
It is not like the weight on a balance beam scale that is part of the measurement.

I think the change at 05:41:22 - ish and one slightly after that can be explained by 2 brief excursions to ~.5g (bit hard to tell exact from graph) at the same time.
Each of those might have 'bumped' the weight enough to shift it slightly.

Last edited by MurphyWasRight; 12th Apr 2019 at 16:44. Reason: Added friction to oil dampening.
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Old 12th Apr 2019, 16:30
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Originally Posted by Icarus2001 View Post
Have you done jet upset or UA recovery in the sim? Low nose is always reduce power.
Wow, who taught you that?
Un load and wings level are first on the list, but when it comes to power, that is as needed.
That means you might need to add power in a low speed, low nose situation. The faster you are on speed, the faster you can pull out.
(Rule of thumb, speed in the 100's - add power, speed in the 200's - power in the mid range, speed in the 300's - cut the power)
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Old 12th Apr 2019, 16:49
  #3911 (permalink)  
 
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UAS

Originally Posted by HundredPercentPlease View Post
Really?

You rotate and get a stall warning, and because your engines are "turning and burning", then you just ignore the stall warning? Has it not occurred to you that you may have your high lift devices incorrectly set, and that the fault was the takeoff config system (Spanair)? Or you have been loaded incorrectly? Or you have an engine indication issue (Air Florida)? Just because your engines are "turning and burning" does not mean that any stall detection on rotation is erroneous. Obviously.
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.

Last edited by L39 Guy; 12th Apr 2019 at 18:41. Reason: Additional thoughts
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Old 12th Apr 2019, 17:07
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Originally Posted by SLF3 View Post

This approach is not specific to Boeing or commerical aviation: it's the way the game is played.
Exactly.

Witness the Ethiopian report declaring that their pilots "did everything correctly". By releasing this blatently incorrect statement prior to the publication of the initial report, they controlled the message.

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Old 12th Apr 2019, 18:33
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"Children of the Magenta Line".
This phrase was by American Airlines pilot Warren Van der Burgh...

Latest on the issue...seems as though in the ITC complaint against Bombardier, B provided some interesting details on the MAX 8...

Before last month’s crash of a flight that began in Ethiopia, Boeing Co. said in a legal document that large, upgraded 737s “cannot be used at what are referred to as ‘high/hot’ airports."

At an elevation of 7,657 feet -- or more than a mile high -- Addis Ababa’s Bole International Airport falls into that category. High elevations require longer runways and faster speeds for takeoff. The Ethiopian airport’s altitude hasn’t been cited as a factor in the downing of Flight 302 and likely didn’t cause the crash. But it could have exacerbated the situation because an airplane’s performance degrades at higher altitudes, said a 737 pilot who flies into high-elevation airports such as Denver and agreed to speak on background since he’s not authorized to talk with the media.

Boeing cited the performance of the 737 Max 8 in a casebrought before the U.S. International Trade Commission in 2017. Boeing charged that unfair competition from Bombardier -- which beat out Boeing for a large order from Delta Air Lines -- threatened its 737-700 and Max 7, the smallest of its upgraded single-aisle jets. By pointing out the limitations of the Max 8, the planemaker sought to preserve market share for the 700 and Max 7.

Boeing stated in a brief filed in the trade case that the “737 Max 7 has greater performance capabilities at challenging airports. In particular, the 737 Max 7 can serve certain ‘high/hot’ airports and has a greater range operating out of constrained airfields.” The brief then cites a number of such airports -- the names of which are redacted -- that the Max 7 can fly into that “the 8, 9 and 10 cannot."

“Larger 737 variants cannot be used at what are referred to has ‘high/hot’ airports,” the brief stated. Certain U.S. airports are unsuitable for the Max 8 “due to a combination of short runway lengths, elevation, temperature, humidity and other environmental conditions."

Documents in the trade case referred to at least 16 U.S. airports considered “high and hot” and therefore unsuitable for the Max 8, though the names of those facilities weren’t made public. Asked during a trade commission hearing to specify which airports, an expert witness for Boeing replied that “sometimes Denver would qualify as that.” The expert, Jerry Nickelsburg, an adjunct economics professor at UCLA, added that “Mexico City certainly qualifies as that.”


https://www.bloomberg.com/news/artic...rtain-airports

Last edited by Smythe; 12th Apr 2019 at 18:46.
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Old 12th Apr 2019, 19:25
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Hot and high has zero to do with both accidents. With two healthy donk’s in a twoholer it is no problem since you have lots of additional power. Why does this totally unrelated topic creep in here?
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Old 12th Apr 2019, 19:38
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All this talk about rwy lenghths and high hot airfields. Nothing to do with those at all. All to do with tweaking and twiddling with an aeroplane to fit the bill and having to write up some software because it is prone to go tits up and that no one has yet managed to train a tame gorilla to take the pilot`s seat. May be one day that too will be possible, but they better be ready to swap the control cables for ships hawsers.
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Old 12th Apr 2019, 20:12
  #3916 (permalink)  
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That double blip of the thumb switches. The big question seems to be, why didn't he continue trimming? I know of no circuitry which will do this, but what happens to that Stab input if it is already exceeding some load limit? i.e., could there be an electrical current limit that clips the power to the Stab motor/clutches if the motor is taking current commensurate with torque that's too high?
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Old 12th Apr 2019, 20:28
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Originally Posted by Loose rivets View Post
That double blip of the thumb switches. The big question seems to be, why didn't he continue trimming? I know of no circuitry which will do this, but what happens to that Stab input if it is already exceeding some load limit? i.e., could there be an electrical current limit that clips the power to the Stab motor/clutches if the motor is taking current commensurate with torque that's too high?
Covered quite well here: https://leehamnews.com/2019/04/05/bj...irst-analysis/
The insufficient trim mystery after re-activation of Electric Trim
After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, it’s hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

As PF holds the nose up with a very high stick force, now for a long time, he’s sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He can’t, he is severely out of trim, holding on to the Yoke with a strong pull force.

Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now, it was a powerful response. Any MCAS attack I now trim against, then I correct my trim if I need to.

But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.

We have Control Column displacement this time, JT610 was Force. If the elevator reacts to these displacements, at the Dynamic Pressure we have, we should have seen the diving stop. The lack of reaction to the large Control Column displacement of two Pilots pulling makes me think we now have blowback. This is not a design fault, we are well beyond Vmo. But it explains the rapid dive, unhindered by the Pilots’ actions.

It’s easy to say “Why didn’t they trim then?”. Because they are going down at 20 degrees nose down (which is a lot, a normal landing approach is 3°) and at 400kts. Then you just pull for all you have. And the aircraft is not reacting to the largest Control Column displacement since takeoff. This makes them pull even harder, the aircraft is unresponsive and they are fighting for theirs and all the passenger lives.
​​​​​​
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Old 12th Apr 2019, 21:17
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Originally Posted by MurphyWasRight View Post
...the suggestion they were very slowly winding the wrong way.
[Not a pilot] FO asked for permission to try "manual," received permission, and gave up, all within an eight second period.

That would seem not related to the gradual change during the (from memory) two and one half minute period.

Last edited by fotoguzzi; 12th Apr 2019 at 21:34. Reason: readability
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Old 12th Apr 2019, 21:41
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Originally Posted by fotoguzzi View Post
[Not a pilot] FO asked for permission to try "manual," received permission, and gave up, all within an eight second period.

That would not seem related to the gradual change during the (from memory) two and one half minute period.
That exchange was at/after the electrical trim was re-enabled, I believe the 'manual' refers to electrical trim switches.

The slow change (wrong direction) was while electrical trim was disabled.
The prelim report did not include much (if any) CVR details from that time, does not mean things were not attempted.

LooseRivets:
That double blip of the thumb switches. The big question seems to be, why didn't he continue trimming? I know of no circuitry which will do this, but what happens to that Stab input if it is already exceeding some load limit? i.e., could there be an electrical current limit that clips the power to the Stab motor/clutches if the motor is taking current commensurate with torque that's too high?
Without knowing exactly where the fdr gets its inputs hard to be sure, but since the automatic and pilot trim inputs are shown separately I suspect the 'blips' are commands not motor activity.

One thing that does comes to mind is a different pilot doing the trim, this matches the same ineffective inputs seen in Lion Air aftert the pilot transfers control to FO.
Is it possible that the last pilots in each case were not used to and or afraid of the long inputs that would have been required?

The only "non pilot" thing I can think of is something that made the switches harder to press/confusing/fail while applying extreme pull.

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Old 12th Apr 2019, 21:44
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Originally Posted by Loose rivets View Post
I'm swinging between both extremes of scenario. However, that balance weight flopping near the end of ET's flight is hard to reconcile, even with Vic's logic.

That slight change of AoA at 05:41:22 - ish, is also troubling me. Why there? Why so consistent before and then after the change? i.e., if it can change at all, why would it remain steady either side of the change?
The correction applied for the difference between AoA vane and AoA body is dependant on Mach number, Pitch rate, Side slip, Flaps, Gear Position and Ground Effect. It is difficult to tell from the 6 figures shown in Fig 9 what form these computations take. Are they look up tables, computed functions, accumulated correction, or serial processed, or what? I’m guessing that they represent different correction lines for different values of the 6 parameters. In which case the single headed arrow line across the Mach number lines could show correction lines to correct AoA Vane to AoA Body from Mach 0 to 0.99, the double headed arrow on Sideslip could indicate + and – sideslip, but there is a single headed arrow for Pitch Rate. Did they not allow for a larger negative Pitch Rate? Could this have led to a negative index in a table? Could some of the computations overflow because of rogue parameters? It could be that one of more of the 6 correction factors used garbage function/table constants to calculate an AoA value of, say 434.5deg, which then ended up as a plausible, but unlikely, 74.5deg on the ARINC 429 bus.

So, the AoA values at the end of ET’s flight (and the 10deg blip at 05:41:22) could be due to the change in the Pitch rate that occurred then, which gave the computations a kick, resulting in different garbage values being picked up. If any of the tables/lines make use of the last computed value of AoA, this can lead to lock in to a particularly high (or low) value. The correction algorithm is far more complex than I first thought, once it goes wrong, any resulting behaviour for a value of AoA is possible!

Whatever damping there may be in the AoA sensor it has to be fairly light otherwise there would be a significant delay on the AoA signal and obviously the pilot does not want to be told he is approaching a stall condition after he has got there! More seriously, if the counterweight without a vane can really get from 35.7 deg to 74.5 deg in 0.75 of a second, then there is very little damping. I do not think it is feasible that the counterweight can then stop, nearly instantaneously, onto the 74.5 deg position, without any overshoot at all, or bouncing off of any end stop that is set at 74.5 deg. Naah, you need software to do that sort of screw up.


Originally Posted by GarageYears View Post
Well, how does that align with ALL the information?
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°

The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state.

There is very little in terms of cause and effect that would satisfy the heater parameter change other than losing the vane itself. (Unless you want to believe this is entirely spurious).

- GY
Firstly, the AoA values are all driven by the correction algorithm, as I have theorised above, mainly the one using Pitch Rate as a driver.

Secondly, good point, I’ve no idea why the L AoA Heat changed state. I’m puzzled as to why the state was On at the beginning, when the outside temperature was 16deg C. However, I’m more inclined to believe that it was spurious than I am to believe there was anything other than a single underlying failure which affected all 3 of the flights.

Vic


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