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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 10th Apr 2019, 17:02
  #3821 (permalink)  
 
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Originally Posted by Icarus2001 View Post
https://utcaerospacesystems.com/prod...-data-systems/

https://www.swiss-airdata.com

https://www.flightglobal.com/FlightP...20-%202855.PDF

The "alternative to AoA vanes" have been in use on commercial jet aircraft for quite a while. A moving vane is old style.


And what do you think is the reason the use of these is not more widespread? I would assume that the main reasons are: mechanical vanes are straightforward, and a standby instrument can just display a value without any computation.

But what's probably more important: they are robust. The "smart sensors" measure pressures at various holes to compute AoA, and these small holes are much more susceptible to icing and being clogged by dirt, in other words, these probes are much more sensitive to less-than-perfect environmental conditions. A partial obstruction of only one of those holes will (perhaps subtly) alter the value. And while that may be fine for an immaculately polished business jet, it is probably not ideal for commercial line operation.

How do you think any of the known accidents involving AoA probes would have been prevented by "modern" sensors?
  • QF 72: A problem with the ADIRU sending wrong data to the flight control computers. Nothing to do with the mechanical properties of the sensor
  • XL Airways Perpignan: AoA vane frozen solid because of improper washing procedures: Could just as easily have happened with "smart" vanes. Possibly slightly different failure more, but small orifices can easily ice over or get clogged
  • Lion Air: We don't know, but possibly also data processing, or else mechanical damage or improper installation. "Smart" probes will also give undefined/wrong values when damaged or installed improperly
  • Ethiopian: quite likely a sheared off vane. Any force that does that would also severely impact a "smart" probe.

So? Just because something is "old style" doesn't mean it's bad, or that newer things are necessarily better. I think AoA sensors without moving parts have not yet proven to be as good as traditional vanes.

Bernd
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Old 10th Apr 2019, 17:15
  #3822 (permalink)  
 
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Originally Posted by bsieker View Post
And what do you think is the reason the use of these is not more widespread? I would assume that the main reasons are: mechanical vanes are straightforward, and a standby instrument can just display a value without any computation.

But what's probably more important: they are robust. The "smart sensors" measure pressures at various holes to compute AoA, and these small holes are much more susceptible to icing and being clogged by dirt, in other words, these probes are much more sensitive to less-than-perfect environmental conditions. A partial obstruction of only one of those holes will (perhaps subtly) alter the value. And while that may be fine for an immaculately polished business jet, it is probably not ideal for commercial line operation.

...
...
So? Just because something is "old style" doesn't mean it's bad, or that newer things are necessarily better. I think AoA sensors without moving parts have not yet proven to be as good as traditional vanes.

Bernd
One excellent use of the 'smart sensors' would be in combination with existing vane style.
This would greatly reduce chances of a common design/environmental fault affecting AoA values.

BTW: The B2 that was totalled in Guam went down due to blocked/miscalibrated sensors, so they are not infallible either.
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Old 10th Apr 2019, 17:17
  #3823 (permalink)  
 
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Don't worry about the video or the trim wheel - EASA has a note from Boeing saying it works throughout the envelope.
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Old 10th Apr 2019, 17:30
  #3824 (permalink)  
 
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The MAX8 engine appears to have a strake on the inboard side at about the 3:00 position. Looks like it is for airflow, but would seem to provide lift at higher AOA.
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Old 10th Apr 2019, 17:38
  #3825 (permalink)  
 
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Originally Posted by bsieker View Post
And what do you think is the reason the use of these is not more widespread? I would assume that the main reasons are: mechanical vanes are straightforward, and a standby instrument can just display a value without any computation.

But what's probably more important: they are robust. The "smart sensors" measure pressures at various holes to compute AoA, and these small holes are much more susceptible to icing and being clogged by dirt, in other words, these probes are much more sensitive to less-than-perfect environmental conditions. A partial obstruction of only one of those holes will (perhaps subtly) alter the value. And while that may be fine for an immaculately polished business jet, it is probably not ideal for commercial line operation.

Bernd
Did you just make that all up?

Maybe your idea of widespread is different to mine as just one manufacturer of this style of probe has quite a broad customer base - including Boeing, LM, Airbus, Northrop Grumman, BAES, Bombardier, Embraer, Sikorsky, Dassault, Gulfstream et al.


Your claim on sensitivity to environmental conditions looks odd for a probe type used on everything from battlefield helicopters and tactical airlifters all the way through to supersonic fighter aircraft and supersonic bombers. Airbus have been using them for nearly 20 years across a number of types!
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Old 10th Apr 2019, 17:42
  #3826 (permalink)  
 
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Originally Posted by Just This Once... View Post
Don't worry about the video or the trim wheel - EASA has a note from Boeing saying it works throughout the envelope.
Is that the video that "Mentour Pilot" deleted?

I am not worried about the video because:

1) They purposely trimmed THE WRONG WAY just to see what happens.

2) It is a simulator and may not accurately reflect actual aircraft operation in the same situation.

Last edited by Lost in Saigon; 10th Apr 2019 at 18:01.
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Old 10th Apr 2019, 17:43
  #3827 (permalink)  
 
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From #3820 “Aviation Week: Boeing Expands MCAS Demos To Speed Lifting Of 737 MAX Grounding”: There is not a single mention of SMYD, obviously Boeing cannot allow the stick shaker to still be driven by an invalid AoA. Boeing would not need to mention SMYD if, for the MAX, they had changed AoA processing and supplied AoA L & R data from the FCC directly to the SYMD via the ARINC 429 bus. It would make sense to do the processing only in one system and may help with CPU loading.

The idea that the invalid AoA problem is a fault, or different faults, in 3 AoA sensors seems to me to be very unlikely, purely from a consideration of reliability figures. AoA sensors are very reliable, from satcom.guru on 28th March:-
Reliability of the AoA sensor was evaluated over a 4-6 year period, with a mean time between unscheduled removals was 93,000 hours. A typical airframe is modeled at about 100,000 hours, so the AoA vane typically last nearly the lifetime of the airplane.
As has been suggested in an earlier post, there could be vulnerability in a new harness which causes a short circuit on a resolver signal. Or (back on my favoured suspect) a latent software fault which affects the processing of the AoA data.

There is an anomaly in the FDR for ET302 (Preliminary Report, page 26) at 05:38:42. It seems to show the Control Column L was pushed forward a second or two before Stick Shaker L started! This could be because the SMYD, if it gets its AoA data from the FCC, is running a cycle behind the FCC. Or it could just be an aspect of the ARINC bus data rates. If I recall correctly, there are various data rates available, and a fast changing control parameter going from one system to another (such as Control Column Position) would go at the fastest rate. A slow changing parameter only for diagnostics (such as Stick Shaker) would go at the slowest rate.
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Old 10th Apr 2019, 17:45
  #3828 (permalink)  
 
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Originally Posted by patplan View Post
An edited GIF version of Mentour Pilot Video...
..Or, you can watch most of it here...
- https://vimeo.com/329558134
Thanks for posting. I knew what was on the video from the text transcript on Bjorn at Leeham News, but it still makes for compelling viewing.

I wonder if Boeing's lawyers saw this last week, and said to the CEO: "If the jury ever sees this, we have lost already"...
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Old 10th Apr 2019, 18:06
  #3829 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Thanks for posting. I knew what was on the video from the text transcript on Bjorn at Leeham News, but it still makes for compelling viewing.

I wonder if Boeing's lawyers saw this last week, and said to the CEO: "If the jury ever sees this, we have lost already"...
I've nothing to do with the aviation industry, but that video is very disturbing, those guys knew it was a simulation, if your (and others) life depended on it, truly frightening. If any pilot on here cares to explain that it's not realistic, or a fair approximation of what happened, please do.

If you don't want to watch the video, the transcript is equally compelling reading...

The original sim session transcript [C=CAPT; F=FO]:
C: We have an IAS disagree.
C: So, IAS disagree memory items.
F: Autopilot if engaged, disengage.
C: Disengaged!
F: Autothrottle if engaged, disengage.
C: Disengaged!
F: Flight directors - Both up
F: With flaps up established a flight path 4 degrees and 75% N1.
C: So, 75% N1.
F: We have 77, 76,...
C: A little bit less...
F: And, there you go.
C: 4 degrees.
F: 4 degrees.

C: So I am trying to establish this now.
F: Check!
F: We are descending...?
F: We probably... Are you feeling troubled with...
F :Any trouble with the flight control?
C: Yeah, I'm trying to trim it but...
C: It continues to trim against me when I'm trimming
C: So state the malfunction, please.
F: Yeah, this doesn't look right. Looks like uh...
F: How do you feel the stabilizer, the trim system?
F: Can you control it?
C: I'm trimming it. It is responding but...
F: It's a runaway stabilizer, if you agree?
C: For every time that I trim backward, it keeps trimming forward.
F: It's trimming forward. Yeah, it's runaway stabilizer.
C: So, runaway stabilizer memory items...
C: And i'm trying to keep this thing at 4 degrees.
F: Control column, hold firmly.
C: I am... [CAPT is holding the yoke firmly with both hands]
F: Autopilot - if engaged, disengage.
C: It's disengaged.
F: Autothrottle - if engaged, disengage.
C: It's..., if you can disengage it for me, make sure that it's disengaged.
F: It's disengaged.
F: And, do you feel that the failure stop?
F: Negative?
C: No, it's still moving.
F: Stab trim cutoff switches to cutoff.
F: OK. It stops. It looks like it stops.
C: You can see now I'm using almost full back pressure here.
F: Exactly.
C: How many degrees nose down?
F: We have 4 units nose down now
C: 4 units nose down?
F: Yup.
C: OK, I'm struggling.
C: I'm actually using almost my full force to keep the aircraft level here.
F: Do you want me to help you?
C: What I would like to do.
C: Just for the sake of exercise, can you trim this forward? [to simulate MCAS trim AND]
C: See if we can reach even zero nose down.
C: And see if I can even hold it.

[FO is trying to crank the trim wheel to reach zero nose down, simulating MCAS AND]

C: So, now we are doing this just as an exercise!
C: Do not try this at home.
C: This...
C: We are at 300 knots now.
F: I'm fighting.
C: I'm sttrugling to to keep this aircraft flying.
F: My god! [FO surprised at how hard it is to trim further nose down]
C: Yeah, the thing is with higher speed the force on the stabilizer will be higher and higher as well.
C: So it becomes almost impossible to move it.
C: So we are now at about 3 degrees.
F: Yup. [FO still tries to continue trimming nose down, the wheels is so difficult to spin]
C: We're still about 3 degrees away from full nose down trim.
C: And I am using everything that I have. [CAPT still holding on to his yoke with both hands]
F: My God ! [the trim wheel barely move for the down trim]
C: This is realistic guys.
C: This is how much of effort it would take to trim the stabilizer at this kind of speed.
C: Umph... [Capt is still trying to hold on to his yoke with his hands]
C: I'm just in control of it, though. But it's getting harder and harder.
C: And remember we're still 2.5 degrees away...
F: My God! [FO still struggles to spin the refused-to-be-spun trim wheel]
C: It's not possible, is it?
C: All right, we stop at that.

C: The reason that we have to try...
C: The reason we have to trim this manually is because the normal trim system wouldn't do this, OK.
C: It would require manual trim to get it away from this.
C: That's fine.
C: Trim it backward. [This time to illustrate the effort to trim the nose back up after "MCAS" brought the AC further nose down]
C: Trim it backward as you can.
F: Oh my God! I couldn't... [FO can't spin the wheel to trim up]
C: OK.
C: Eh...
C: Juan, press the red button! [CAPT called the sim operator...]
C: Press the red button now. [to stop the sim session]
C: This is at 340 knots.
C: And the trim is at...It's still at almost 2.5 degrees.
F: Yeah, 2.5 degrees.

Alchad

Last edited by Alchad; 10th Apr 2019 at 18:18.
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Old 10th Apr 2019, 18:30
  #3830 (permalink)  
 
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Alchad

I've nothing to do with the aviation industry, but that video is very disturbing, those guys knew it was a simulation, if your (and others) life depended on it, truly frightening. If any pilot on here cares to explain that it's not realistic, or a fair approximation of what happened, please do.
Many people (still) blame the pilots for getting into that situation, by not taking action sooner. All sorts of clever answers are possible, for those sitting at home, and having had time to read the accident report.
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Old 10th Apr 2019, 18:50
  #3831 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
One excellent use of the 'smart sensors' would be in combination with existing vane style.
This would greatly reduce chances of a common design/environmental fault affecting AoA values.
And it is not just AoA vanes that are a Common Mode Failure by design, the 3 (or 4) pitot tubes for measuring TAS are all same technology, all located near to one another. The purpose of AOA sensors is to detect an imminent stall; a more direct measure (possibly a second source for a plausibility check) would be a pressure sensor built in to the upper and lower wing surface. It need not use holes, if something as mundane as a mobile phone can distinguish between a tap and a swipe, there must be other new technologies out there that could be used.

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Old 10th Apr 2019, 18:59
  #3832 (permalink)  
 
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Originally Posted by Lost in Saigon View Post
Is that the video that "Mentour Pilot" deleted?

I am not worried about the video because:

1) They purposely trimmed THE WRONG WAY just to see what happens.
They trimmed the wrong way not "to see what happens", but to replicate MCAS trimming the wrong way, because electric trim can't trim nose down so much with the flaps up, as MCAS can.

At the end they tried to trim THE CORRECT WAY, but even with the trim at just 2.4 units from full nose down it was almost impossible for one person.

2) It is a simulator and may not accurately reflect actual aircraft operation in the same situation.
I don't understand why you are not worried. Is it because you believe it will be much easier on a real aircraft in the same situation? If that's the reason, what is the basis for your belief?
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Old 10th Apr 2019, 19:25
  #3833 (permalink)  
 
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Originally Posted by Just This Once... View Post


Did you just make that all up?

Maybe your idea of widespread is different to mine as just one manufacturer of this style of probe has quite a broad customer base - including Boeing, LM, Airbus, Northrop Grumman, BAES, Bombardier, Embraer, Sikorsky, Dassault, Gulfstream et al.


Your claim on sensitivity to environmental conditions looks odd for a probe type used on everything from battlefield helicopters and tactical airlifters all the way through to supersonic fighter aircraft and supersonic bombers. Airbus have been using them for nearly 20 years across a number of types!
Have you ever looked at the nose of an A350? It clearly has a lot of mechanical vanes, three alone for sideslip angle, and some combined probes (pitot plus mechanical vane). Same for the A380. So no, Airbus is not relying on fancy smart probes, although they may use them alongside traditional vanes.

And you are aware that the picture is from a sales brochure by the manufacturer. Maybe Airbus evaluated such probes, which would be enough for them to claim the type on their list. You may also notice that the picture uses the weasel word "... programs", which could mean anything. A "program" can also just be a theoretical evaluation, with a final decision against it.

There are also mechanical vanes on the A400M, the 787, the CSeries, etc. Business jets, yes, but other than the E2 I haven't seen one airliner without them. Not exactly widespread. And that's all just because ... manufacturers cannot be bothered to use modern technology?

Bernd
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Old 10th Apr 2019, 19:33
  #3834 (permalink)  
 
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Originally Posted by MemberBerry View Post
They trimmed the wrong way not "to see what happens", but to replicate MCAS trimming the wrong way, because electric trim can't trim nose down so much with the flaps up, as MCAS can.

At the end they tried to trim THE CORRECT WAY, but even with the trim at just 2.4 units from full nose down it was almost impossible for one person.



I don't understand why you are not worried. Is it because you believe it will be much easier on a real aircraft in the same situation? If that's the reason, what is the basis for your belief?
In the video they spent far too long fighting the control forces before attempting to operate the trim cutout switches. Maybe they were trying to represent the lowest common denominator in pilot skill? MCAS does not operate if the pilot toggles the trim switch so they should have been able to operate the trim cutout switches before the aerodynamic load became excessive. "Should Have" is important but we'll have to wait for the full report to find out why they didn't.

I have no idea whether or not it would be easier in a real aircraft. I just don't trust that a simulator can accurately reproduce what actually happens. It would be interesting to hear from someone who has actually experienced excessive airloading of the stabilizer trim in a B737.
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Old 10th Apr 2019, 20:05
  #3835 (permalink)  
 
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Originally Posted by VicMel View Post
I absolutely agree. The aviation authorities have the hardest of evidence possible that “average” pilots are unlikely to cope. Boeing’s dilemma is this then means the MCAS system (at least) has to be considered as a “catastrophic” safety critical system. The MCAS software then has to be “Level A” according to DO-178C.

IMO no amount of software patching can turn a Level C software package into a Level A.
Has it been stated anywhere what design assurance level (DAL) the new MCAS software will be?

I have read there are several changes:
  • Compare L & R AOA (and inhibit if they disagree, and display raw AOA values)
  • Only allow 1 trim application
  • Limit MCAS input to less than control column authority
But nowhere have I seen what the DAL is going to be. Since the hazard assessment seems to be where the errors started, allowing one sensor, what's the new hazard assessment?
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Old 10th Apr 2019, 21:11
  #3836 (permalink)  
 
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Originally Posted by VicMel View Post
And it is not just AoA vanes that are a Common Mode Failure by design, the 3 (or 4) pitot tubes for measuring TAS are all same technology, all located near to one another. The purpose of AOA sensors is to detect an imminent stall; a more direct measure (possibly a second source for a plausibility check) would be a pressure sensor built in to the upper and lower wing surface. It need not use holes, if something as mundane as a mobile phone can distinguish between a tap and a swipe, there must be other new technologies out there that could be used.
How about this - you could drill a hole in the leading edge of the wing, slightly below the stagnation point. Using some flexible tubing, you could connect this hole to a kazoo or harmonica mounted in the cockpit. At a high angle of attack, the stagnation point will move below the hole, and a vacuum will exist at the hole, drawing air through the tube and sounding the kazoo.

You could even test it during pre-flight by applying oral suction. One would presume that this would be an FO task.
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Old 10th Apr 2019, 21:43
  #3837 (permalink)  
 
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hope it was the old version:
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Old 10th Apr 2019, 21:46
  #3838 (permalink)  
 
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Originally Posted by slacktide View Post
How about this - you could drill a hole in the leading edge of the wing, slightly below the stagnation point. Using some flexible tubing, you could connect this hole to a kazoo or harmonica mounted in the cockpit. At a high angle of attack, the stagnation point will move below the hole, and a vacuum will exist at the hole, drawing air through the tube and sounding the kazoo.

You could even test it during pre-flight by applying oral suction. One would presume that this would be an FO task.
Crafty FOs could carry one of these to test the kazoo......
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Old 10th Apr 2019, 22:14
  #3839 (permalink)  
 
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Originally Posted by slacktide View Post
How about this - you could drill a hole in the leading edge of the wing, slightly below the stagnation point. Using some flexible tubing, you could connect this hole to a kazoo or harmonica mounted in the cockpit. At a high angle of attack, the stagnation point will move below the hole, and a vacuum will exist at the hole, drawing air through the tube and sounding the kazoo.

You could even test it during pre-flight by applying oral suction. One would presume that this would be an FO task.
What you have described is the old Safe Flight stall warning system which used a moveable vane at the stagnation point instead of an orifice. This stall warning system has been around light aircraft since about 1946 or so.

Cheers,
Grog
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Old 10th Apr 2019, 22:40
  #3840 (permalink)  
 
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Originally Posted by capngrog View Post
What you have described is the old Safe Flight stall warning system which used a moveable vane at the stagnation point instead of an orifice. This stall warning system has been around light aircraft since about 1946 or so.

Cheers,
Grog
No, the system he is describing does not use a vane.
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