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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 6th May 2019, 14:39
  #5001 (permalink)  
 
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There's no date on that Boeing statement. Was it issued before or after the Ethiopian crash?
It showed up on the website on May 05, 2019. at around noon.

Strictly from a technical perspective, however, it needs to be pointed out that if a 737 crew were to receive an "AOA Disagree" message and go to the appropriate NNC, that checklist would simply direct them to the "IAS Disagree" checklist and/or the "ALT Disagree" checklist as appropriate
Well, that was my question, if you did get the alert, what would you do? With MCAS, it appears that it uses one specific AoA vane? (or just one vane) I am unclear on this.
Cutting off MCAS does not solve the issue of the reason it was created in the first place, lift from the nacelles.
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Old 6th May 2019, 14:57
  #5002 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Thanks for the link. It gets worse:

Quote extract...

But in the last several weeks, Boeing has been saying something different. Mr. Tajer said the company recently told American pilots that the system would not alert pilots about any sensor disagreement until the aircraft is 400 feet above the ground.

Unquote

My emphasis added. This is a critical point that was touched on previously. It is impossible to get a reliable AOA value until there is significant forward airspeed. Plus it takes time to compare the two values, and trigger the AOA disagree warning. By then the aircraft is airborne. Its a bit too late. If it was fitted and worked, which it didn't.
Im surprised this didn't attract more comments, perhaps it got missed in the flurry of recent posts? Just wondered how much of a "wow" comment it is, and also whether the 400 feet limit would presumably also apply to MCAS as it would suggest that an input check is performed before the AOA signal is allowed to be used? There was talk way way back about a height limit on MCAS intervention but don't think it ever got resolved.

Alchad
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Old 6th May 2019, 15:00
  #5003 (permalink)  
 
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Originally Posted by 737 Driver View Post
During our trip, we discussed a number of issues that had come out of the recent MAX crashes. During this conversation, he confessed that before these accidents, he did not even know the stab trim wheel had a stowable handle and had never been trained in its use. Think about that for a moment. Also consider that a freshly-minted 737 Captain would have received the exact same training.
..
He (fleet manager) added a telling remark, however, that stab trim malfunctions had never been a statistically significant problem at our airline, implying of course that the training events our pilots are exposed to constantly needed to be justified by historical data.
...
This supports my impression that the manual trim system as originally designed has been continually degraded both by training and physical changes such as smaller wheel and removal of separate auto only cutout option.
At the same time the sources of runaway trim have increased as more automatic systems use the trim, NG sts and other? , MAX + mcas and other?.

Can not help but think that the safety analysis used a faulty evaluation of manual trim system, mechanical and pilot training, when assessing MCAS impact, falling back on grandfathered original analysis of effectiveness/useability.
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Old 6th May 2019, 15:11
  #5004 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
@737 Diver:
The issue here, having just gone through the last 7 pages of this thread, remains a multi party setting up of this crew (as I see it).
1. Boeing and various companies were chasing a dollar/profit objective, and the AoA miscompare "alert" was apparently optional equipment.

2. A primary flight control is moved by an aircraft sub system with no pilot in put, but (as has been discussed at length) a number of ways of disabling it.

3. Training on this subsystem: of questionable quality. Doubly so due to wide variation between air line companies in how much (in terms of time and money) they invest in their crews, not just for the upgrade to Max but in general.

4. Crew training(??) / inexperience becoming an international norm.

5. Over-reliance on automation becoming an international norm.

6. Arriving at your points in your latest post, (none of which seem unreasonable to me, but I don't fly 737) the above mentioned factors suggest that unless you are in a company who values crew competence, and puts money / time / resources toward that core value, your crews are open to being set up - not only for the startle factor increasing a challenge, but incomplete systems knowledge (and practice with it) getting in the way of timely and correct decision making when dealing with a systems malfunction. Years ago when I was running sim training the ability to do some "free play" at the end of a session to test where a crew got oversaturated with systems malfunctions/emergencies was good training, and a lot of crews really appreciated them.
Meme/clue for the non pilots in the audience here: when a malfunction turns into an emergency (or a fatal crash) to simply blame the pilots is to overlook that layers of human endeavor and responsibility that got them to that point.

7. (Pax Britannica made some interesting points previous but I lost my train of thought). The cockpit gradient in a given cockpit does not develop in isolation from cockpit / corporate culture, which is also informed by larger cultural issues regarding authority. It is unclear how that played out for ET to me, and is one of those hard to quantify factors.

8. A company (be it ET, Lion, or perhaps if things had played out differently, United or American?) has a powerful financial motive to move the blame indicator arrow to point ONLY at the manufacturer. (And the single point of failure issue that looks to be a root causal factor gives them fair grist for that mill). Some of this is cultural, some of this is purely financial due to how litigation works.

9. In the time between Lion Air and ET: what training, what systems training, and what crew training with related malfunctions did this crew have? What are the effects of negative training, and how do those play out in a cockpit?

10. Recency and upset training was mentioned above. I'll offer an idea here: any malfunction that is related to the movement of primary flight controls is subject to a recency factor (as seen in the AF 447 accident).

Were they, the crew in ET, set up?
At least in part, I offer that the answer is yes. The system that set them up all of the world's airline companies are a part of, and are core players in. So too are regulators, and nations.

I can't disagree with the general point that the pitch and power chorus are making (this singing group is once again on stage was they were for most of the AF 447 discussion on PPRuNe) . Power plus attitude equals performance.
But are people really being trained that way anymore?
Are their behaviors being incentivized to ground their operation of aircraft with that fundamental principle foremost?
If not, why not?
The corporations who make their money in this business (be it manufacturing, operating, or training people to operate the equipment) need to answer that question. So who is holding them all to account?

Aside: I do not believe that there is now an international standard of what a professional pilot is - I have seen some appeal to that thought - no matter how badly I wish that were true.
There may once have been such a standard. (But hey, all that is now needed is a concierge, eh? Tech is magic! (/sarcasm off))
There's a lot of lip service paid to it, though, and professional pilots (those who are the real deal) are rightly dismayed to see the profession that learned hard lessons over the course of a century, under attack. The two dead men (and their passengers) from ET are casualties in a war that seems to be going on between price and professionalism, and the use of automation to replace human function.

I agree 100%...+1
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Old 6th May 2019, 15:54
  #5005 (permalink)  
 
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Alchad, Ethiopian airliner down in Africa

No ‘wow’ response because an AOA Disagree alert has little value for pilots. There is no third system to resolve the ambiguity - which AoA is correct - not known; what can I do about it - nothing, info only (or distraction). Furthermore an alert could contribute to misdiagnosis in the UAS drill; stick shake + EFIS low speed awareness on the ‘left side’, this might incorrectly bias thoughts to the left, - speed correct - aircraft is slow.
Whereas the Air Data Disagree alerts for Speed / ALT each have a third, standby instrument which the crew can use to arbitrate and choose the most valid pairing; standby + right side = right Speed is best.
So without means of arbitration the AoA alert has little value.

From an engineering view, particularly with hindsight, AoA Disagree could have been used in the original MCAS design. It wasn’t because that design assumed that the effects in the accident would not occur - all of which were incorrect.
Limiting these problems using AoA Disagree provides an engineering solution. However for the crew, retaining the AoA alert would not clarify the accuracy of AoA - so don’t display the alert nor the optional gauge when there is disagreement.
The most important absence is the annunciation that MCAS is inoperative, which with a caution that flight in some (few) areas of the fight envelope requiring careful handing.






Last edited by safetypee; 6th May 2019 at 16:01. Reason: Typo
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Old 6th May 2019, 15:57
  #5006 (permalink)  
 
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What is the big issue?

Among others, 737 Driver is getting a lot of flack in this thread because some people see his contributions as trying to deflect blame away from Boeing and on to the pilots. I would not be so harsh, but suggest that pilots tend to look at issues from a pilots perspective. There is little doubt that disabling electric trim at an early stage would have prevented these accidents. However, one could also suggest that disabling electric trim before all flights would have prevented these accidents or simply grounding the MAX series would have prevented the accidents.

A little flippant yes, but it is the reason for some emotional statements. None of the pilots could reasonably be accused of anything other than an innocent mistake. Boeing on the other hand did not make an innocent mistake they took a calculated risk... a risk that did not pay off. It was not an innocent mistake at all. It is the difference between doing something wrong and making a mistake. 737 Driver accepts that MCAS should not be enabled when AoA disagree (or so I understand). Boeing must have understood this issue long before Lion Air, and certainly after Lion Air.They should have grounded the MAX to resolve the matter. That is why a little emotion is creeping into this thread.

737 Driver is tending to argue pitch and power is the solution but underplaying that pitch cannot be achieved if it is running away. Earlier on in the thread, 737 Driver said runaway could be arrested by the knee of the pilot... not sure that is following procedure or is even possible. 737 Driver is insistent that electric trim can be used to counteract MCAS. If the publications of Boeing are accurate, that is true.

However, it is difficult to believe that the in the Lion Air and ET302 incidents that the pilots were not trying to use the thumb switches to counteract MCAS. Maybe they were not, maybe they, for some reason, thought that they could not. I still have some doubts because it does not seem to add up. What is certain is that had they reacted quicker and hit the cut-out switches earlier, they probably would have been in good shape. Of course, the FDR suggests that the pilots did not use much electric trim, but it is not conclusive because thumb switch input is not recorded.

I am a little skeptical why the voice transcripts of ET302 have not been published. I suspect some legal eagles have stuck their oar in. The transcript could be exculpatory or damning to some of the parties. Perhaps some parties do not want those kinds of conclusions made just yet. It is probably for the best to take a little more time to do a thorough investigation, despite the public desire to know what happened. All too much truth has come out already for Boeing's liking. Perhaps the tip of the iceberg?

Last edited by wheelsright; 6th May 2019 at 17:14.
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Old 6th May 2019, 16:01
  #5007 (permalink)  
 
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Originally Posted by 737 Driver View Post
If I recall correctly, the "5 second" remark was specifically in reference to a certain set of steps on the runaway stab trim checklist. Apparently there is a "demo" video on YouTube that gives the impression that it takes longer, and someone was under the impression that this length of time was one of the things working against the crew. I was simply pointing out that it could have been done quicker. In another post, however, I also pointed out that the crew could take all the time they needed to get the aircraft back to neutral trim as long as one of the pilots was, yes, FLYING THE AIRCRAFT and managing the trim using the yoke switch.
I recall it a bit differently. It was a longer exchange starting with a comment about the first step in your mantra. I claimed that "turning off the magic" is made more difficult on the MAX, because it contains an additional bit of magic that can't be turned off without losing manual electric trim as well. As a solution I proposed introducing a software update (since a hardware change like rewiring the cutout switches differently would be more costly), which would allow the pilots to disable MCAS and other types automatic electric trim without losing manual electric trim. You replied that the new feature would involve more troubleshooting, and the philosophy is that pilots should not troubleshoot problems, and procedurally they shouldn't fiddle with the cutout switches. I replied that the runway stabilizer memory items already look a bit like troubleshooting, saying "do this, if that doesn't work do that, if that doesn't work finally do that". What I meant was that a bit more troubleshooting in addition to the existing troubleshooting steps wouldn't be the end of the world. For example the "fiddling" part could be added as deferred items. Especially since two sets of pilots experiencing MCAS did just that. They fiddled with the cutout switches after initially disabling stabilizer trim.

Then you replied that those "troubleshooting" steps in the memory items can be done in "under 5 seconds". I felt that sounded a bit like an exaggeration. First of all the pilot flying would have to hold firmly the control column. This means he would have to rely on the pilot not flying to actually execute rest of the memory items, since his hands are busy. I assumed the pilot not flying will not just do the rest of the items blindly and hastily, without confirming them with the pilot flying first, so I didn't see how that that can be done in under 5 seconds. So I replied with a partial transcript of a Mentour video, demonstrating the execution of the memory items, where the "troubleshooting" part took 43 seconds. Mentour is a captain with over 10000 hours experience on the 737. He is also a line training captain, type rating instructor, and type rating examiner.

I agree that in the demo video they were not executing the memory items as fast as possibile, and in a real emergency it would probably be wise to execute them faster. What I didn't mention was that, including problem identification, it actually took them 83 seconds between the start of the runaway and using the cutout switches, including the time needed to identify the problem. The full transcript and the link to the video by Mentour is in one of my older posts in this thread, here: Ethiopian airliner down in Africa

It is possible Mentour was exaggerating by making the execution of the memory items too long and too formal. Or you were exaggerating with your "under 5 seconds" claim. Or both. Alternatively there may be some misunderstanding on my part.

After your "don't tell me how to fly the plane" post I took a break from posting yesterday to allow the things to calm down. Even if I don't agree with everything you say, I appreciate your informed contributions to this forum, and that you are trying not to let the discussion go "into the weeds". As for me, I'm just a passenger that is interested in this MAX saga. I only post when somebody makes claims that are clearly wrong without anybody contradicting him (for example the "the pilots allowed the plane to reach 500 knots without doing anything" post, or the "pilots in the previous Lion Air flight immediately used the cutout switches"), or when I feel that the facts or opinions I post are valuable to the discussion.

Unfortunately I'm not very good at interacting with people, and I'm sorry if my posts may seem disrespectful, I am just giving my honest opinion.


Now to different topic, the AoA disagree light. First, we have the revelation that Boeing didn't know that it doesn't work if the AoA display optional feature was not installed. OK, that's understandable, it's a bug that has slipped through testing. It happens. Then they say they analyzed the impact and they concluded it doesn't affect the safety. OK, fair enough, a lot of pilots have expressed similar opinions.

But then there is decision to not inform either the FAA or the airlines about the problem. Hiding this information IS actually a safety issue, in my opinion. OK, let's say 95% of the pilots don't care about the AoA disagree light. But the remaining 5% might be confused in a AoA disagree situation, assuming the disagree light works correctly and there is nothing wrong with the angle of attack vanes. Instead those pilots may suspect issues with the pitot probes the static ports or some other issues when they get a false stick shaker.

And even the part about the disagree indicator itself not being a safety feature is debatable. For example, after the previous Lion Air flight, if this indicator worked properly its activation might have been recorded in the flight and maintenance log, and the maintenance crew might have tested replaced the faulty vane, and we wouldn't have the Lion Air accident.

But then, the cherry on top is Boeing not even knowing how their planes work. First claiming that when the related option is installed AoA disagree light can activate on the ground, then realizing after a few months that actually you need to be at least 400 feet above ground level for it to activate. I don't even know what to say about that. They didn't give the contractor that implemented that piece of software exact specifications about how it should work? If they did, how is it possible they didn't know? Did somebody later assume it works just like on the NG, without checking the documentation before telling the airlines? I assume it works on the ground for NGs, during the takeoff roll, otherwise I can't find any reasonable explanation for this surreal display of incompetence on Boeings part.
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Old 6th May 2019, 16:09
  #5008 (permalink)  
 
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Originally Posted by safetypee View Post
Alchad, Ethiopian airliner down in Africa

No ‘wow’ response because an AOA Disagree alert has little value for pilots. There is no third system to resolve the ambiguity - which AoA is correct - not known; what can I do about it - nothing, info only (or distraction). Furthermore an alert could contribute to misdiagnosis in the UAS drill; stick shake + EFIS low speed awareness on the ‘left side’, this might incorrectly bias thoughts to the left, - speed correct - aircraft is slow.
Whereas the Air Data Disagree alerts for Speed / ALT each have a third, standby instrument which the crew can use to arbitrate and choose the most valid pairing; standby + right side = right Speed is best.
So without means of arbitration the AoA alert has little value.

From an engineering view, particularly with hindsight, AoA Disagree could have been used in the original MCAS design. It wasn’t because that design assumed that the effects in the accident would not occur - all of which were incorrect.
Limiting these problems using AoA Disagree provides an engineering solution. However for the crew, retaining the AoA alert would not clarify the accuracy of AoA - so don’t display the alert nor the optional gauge when there is disagreement.
The most important absence is the annunciation that MCAS is inoperative, which with a caution that flight in some (few) areas of the fight envelope requiring careful handing.
Not really true. A MAX pilot should immediatley disable electric trim if AoA disagree, period. That is what we now know. We also know that the system should disable MCAS in the event off AoA disagree and Boeing did not provide that logical functionality. Otherwise agreed.
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Old 6th May 2019, 16:31
  #5009 (permalink)  
 
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Originally Posted by 737 Driver View Post
I do not disagree in theory, but IMHO, the reality is that the training standards dictated by Boeing have been catering to the lowest common denominator for years. They have a strong incentive to sell aircraft across the entire spectrum of airlines and countries regardless of the depth and quality of their aviation heritage. Requiring a higher level of demonstrated skills for the operator potentially translates into higher costs and lost sales.

Sadly, this thought process does not stop at Boeing. I recently had an opportunity to fly with FO who was relatively new to the 737. During our trip, we discussed a number of issues that had come out of the recent MAX crashes. During this conversation, he confessed that before these accidents, he did not even know the stab trim wheel had a stowable handle and had never been trained in its use. Think about that for a moment. Also consider that a freshly-minted 737 Captain would have received the exact same training.

After I picked my jaw up off the floor, I proceeded to personally give the FO the training he had missed. Afterwords, I shared my concerns with my Fleet Manager and told him in no uncertain terms that our training programs needed a thorough review. The Fleet Manager replied that this was already in progress, and stated that our training programs were constantly being reviewed for improvement. He added a telling remark, however, that stab trim malfunctions had never been a statistically significant problem at our airline, implying of course that the training events our pilots are exposed to constantly needed to be justified by historical data. I told him that if the MAX accident had occurred at our airline, the family of those who perished would have been rightfully angered if it had come to be known that the crew had not been properly trained in a runaway stab procedure because the airline considered it to be a statistically insignificant event.

The degradation of pilot training and standards is a worldwide problem. It is being driven in large part by the beancounter mentality that attempts to justify every cost. Unfortunately this approach forgets that there are some costs that cannot be easily quantified, and eventually a price will be paid in bent metal and broken bodies. Sadly, even if the industry will not openly admit it, there seems to be an underlying assumption that there is an acceptable hull loss rate and that little will change until the body count goes up.
Could not agree more.
A few companies and almost two decades ago I upgraded in a small company flying 50-seaters. Before they let you on the line there was extensive checking before upgrade started, and OE/line-training till every deficiency was corrected or you were send back to the right seat, SIM training was something different every half year, with a specific training syllabus send out a few weeks prior to prepare. I upgraded a few years ago on the A320, got 7(!) sectors of OE and was send on my way. In my first few months, and flying with new FOs (company growing fast) I had quite a few things I had never seen before: no FD take-off due to dispatched with the engines in N1 rated mode, FD deferred and several others I had never seen online or in the SIM. Most of the training now is checking the required boxes, same scenario every time, and there are so many items you are doing "250 to the marker" CATIII and OEI/SE because of time constraints.....
I am lucky my company lets me fly raw data/AP/AT off except when required by regulations (RNAV SID/LO-VIS/AUTO landing) so I have been able to stay current, and show a lot of "inexperienced" FOs all these things, but it really should be trained to proficiency before getting to the line.

Also, I really agree with your take on the automation dependency issue.
Boeing needs a company wide overhaul of their certification department, with much more regulatory oversight to rebuilt confidence. The massive mistakes made in certifying MCAS, (and all the other surrounding issues like AOA discrepancy warnings left inactive due to third party software (no excuse IMHO)) makes me believe heads should roll at every level.
Having said that, just because Boeing messed up. doesn't mean the pilots didn't. There have been more instances of LOC in-flight were the only crew action was a frantic attempt to re-engage the AP. If that is the best you can do, you are not trained/capable to be in the cockpit. Most of what the pilots did in the 3 flights we are talking about speaks to severe training/handling issues.
Continuing a flight with the stick shaker, and then only writing up reverse STS trim is IMO on of the primary causes for the first crash.
Using trim two dozen times to correct MCAS, but never interrupting the MCAS while it was trimming (so only re-active, never pro-active), and still not switching the trim off, or reducing power?
Switching the trim off while out of trim, but not reducing power, and no hand trimming till it was too late?
None of theses events had a single easy checklist that would have resolved everything, but it does still say in the manual, that there is no checklist for every conceivable problem, and pilots are expected to be able use their skills to control the aircraft, while handling unexpected situations.
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Old 6th May 2019, 16:32
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Not that simple, in a climbing turn, AoA will always disagree.
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Old 6th May 2019, 16:46
  #5011 (permalink)  
 
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Originally Posted by Smythe View Post
Not that simple, in a climbing turn, AoA will always disagree.
For all their blatantly obvious faults, I don't think Boeing is incapable of designing a working AOA disagree system. They set the threshold around 5deg I believe. I would think that is based on test/simulations showing "climbing turns" will not give an AOA disagree more than 5 degrees. (also don't think the it needs to be a turn, or climbing. The AOA disagree will get higher for higher AOA, especially in combination with un-coordinated flight).
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Old 6th May 2019, 16:58
  #5012 (permalink)  
 
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Originally Posted by Smythe View Post
Not that simple, in a climbing turn, AoA will always disagree.
IMHO it is that simple. There are ordinarily circumstance that there will be disagreement or unreliable data. For example, before the aircraft has sufficient speed before takeoff, AoA is meaningless. Boeing has included some other criteria that disable MCAS that is not thoroughly documented but touched on. The left and right FCC is a black box device that is programmed to take account of various factors. The magic of computers is that they can take account of many factors that humans will take longer periods to process. AoA/MCAS could be programmed to take account of many factors that could occur normally and fail-back in other circumstances. Boeing itself has published advice to disable electric trim under certain circumstance but left that that to the pilots. It is very doubtful that MCAS should continue to have authority when AoA is clearly unreliable.

What is the published procedure for AoA disagree notification when installed?
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Old 6th May 2019, 16:58
  #5013 (permalink)  
 
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More from Seattle Times:

Tajer said the American pilots were told in the meeting that on the flight deck of their 737 MAXs, the AOA disagree light would have lit up on the ground and so, because that’s a “no-go item,” the plane wouldn’t even have taken off. However, Tajer said that within the last two to three weeks, “we are now learning that, unlike Boeing told us in November, the warning light actually is inhibited on the ground.”

“We are being told by Boeing that the AOA Disagree Alert … is inhibited until 400 feet above ground level,” he said Sunday. “We are currently awaiting written confirmation of this AOA Disagree Alert limitation as it is not detailed in any 737 flight crew manual.”


https://www.seattletimes.com/busines...t-told-no-one/

At 400 feet, the light comes on, then what? (the 5 second memory rule?)

AoA/MCAS could be programmed to take account of many factors that could occur normally and fail-back in other circumstances.
It already does. AoA is never a direct reading from the vane, it passes through many levels of algorithms depending on circumstances and conditions.

Last edited by Smythe; 6th May 2019 at 17:10.
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Old 6th May 2019, 17:02
  #5014 (permalink)  
 
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Originally Posted by MemberBerry View Post
Then you replied that those "troubleshooting" steps in the memory items can be done in "under 5 seconds". I felt that sounded a bit like an exaggeration. First of all the pilot flying would have to hold firmly the control column. This means he would have to rely on the pilot not flying to actually execute rest of the memory items, since his hands are busy. I assumed the pilot not flying will not just do the rest of the items blindly and hastily, without confirming them with the pilot flying first, so I didn't see how that that can be done in under 5 seconds.
It is very clear you're unable to grasp the concept of how a memory item procedure is conducted; it is certainly not how you suppose it to be. You are conflating a NNC procedure and a memory item procedure. Stop wasting our time sharing your opinions on things you know nothing about. This is rubbish speculation and it is also happens to be 100% wrong.
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Old 6th May 2019, 17:12
  #5015 (permalink)  
 
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Originally Posted by Smythe View Post
More from Seattle Times:

Tajer said the American pilots were told in the meeting that on the flight deck of their 737 MAXs, the AOA disagree light would have lit up on the ground and so, because that’s a “no-go item,” the plane wouldn’t even have taken off.However, Tajer said that within the last two to three weeks, “we are now learning that, unlike Boeing told us in November, the warning light actually is inhibited on the ground.”

“We are being told by Boeing that the AOA Disagree Alert … is inhibited until 400 feet above ground level,” he said Sunday. “We are currently awaiting written confirmation of this AOA Disagree Alert limitation as it is not detailed in any 737 flight crew manual.”

https://www.seattletimes.com/busines...t-told-no-one/
That statement about the first meeting seems really wrong. The AOA won't work without the plane moving through the air (preferably in the direction the nose is pointed). Because the vane has a counterweight inside it will be more than happy to sit at a random angle, until somewhere during the T/O roll the will start indicating AOA. The 400' sounds more reasonable to me, as it will give time for factors as side-slip due to crosswind T/O to dissipate.
The biggest issue for me is that again there is a system that is incompletely in the Boeing FCM.
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Old 6th May 2019, 17:28
  #5016 (permalink)  
 
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I am not a pilot, but I am curious. What is the technical reason for not having the AoA sensors on the same side of the aircraft? Be gentle, I am not a pilot.
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Old 6th May 2019, 17:29
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Originally Posted by Smythe View Post
More from Seattle Times:

It already does. AoA is never a direct reading from the vane, it passes through many levels of algorithms depending on circumstances and conditions.
Re your quote from my comment... I thought that is what I said, sorry if it was not clear. The AoA signal is routed to the FCC's; thereafter it is processed. For reasons that are not clear, MCAS was intended to remain active when AoA was unreliable. Part of the problem is that left and right is separated and the the left hand does not know what the right is doing, so to speak. Disagree seems to be separate from the FCC's but I stand to be corrected.

The signal from the AoA has to have all kinds of mapping and algorithms to provide clean data. Vibration, noise, sudden turbulence, inertia are but some of the issues that must be processed out. However, the question is why substantial disagreement between sensors was not regarded as an important factor in disabling MCAS automatically?
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Old 6th May 2019, 17:34
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Originally Posted by wheelsright View Post
Not really true. A MAX pilot should immediatley disable electric trim if AoA disagree, period. That is what we now know. We also know that the system should disable MCAS in the event off AoA disagree and Boeing did not provide that logical functionality. Otherwise agreed.
Uh...., no. I could go into all the reasons why one shouldn't, but can you just take my word for it?
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Old 6th May 2019, 17:37
  #5019 (permalink)  
 
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wheelsright:

However, the question is why substantial disagreement between sensors was not regarded as an important factor in disabling MCAS automatically?
This is the question which Boeing needs to answer.

Boeing has now revealed that the MAX had a system which compared the values supplied by the Left and Right AoA sensors. This system was supposed to flag an alert to the crew when the disagreement between the sensor values exceeded, presumably a set threshold. This AoA disagree alert was not actually implemented due to an error/oversight which the company discovered in 2017.

Thus, it seems the MAX had a means of checking the validity of AoA sensor values from day one. I cannot comprehend why this AoA disagree signal was not used by the MCAS system to inhibit nose-down trim inputs to the HS for as long as the AoA disagree signal=TRUE. Had this been done, it is unlikely the Lion Air and Ethiopian crashes would have occurred.
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Old 6th May 2019, 17:42
  #5020 (permalink)  
 
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Originally Posted by wheelsright View Post

What is the published procedure for AoA disagree notification when installed?
.
The "AOA Disagree" procedure is a simple redirect to the "IAS Disagree" or "ALT Disagree" procedure because that is the immediate impact of a bad AOA input. The "IAS Disagree" procedure is a redirect to the "Airspeed Unreliable" procedure.

What is currently not well covered in any of the current 737 procedures is that a faulty stall signal that is generated by a bad airspeed or AOA input will create a number of ancillary system issues that must also be addressed. On the other end of the spectrum, an erroneous high airspeed input will cause a few problems, but not nearly as many as the low airspeed case.
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