MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
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Which is more a commentary on the decrepit state of modern journalism. I've seen some really good investigating reporting on the MAX, and a lot of bad as well. The good reporters already have connections inside the industry or have a sufficient standing that new sources will contact them directly. An aviation-centric reporter who doesn't know his/her stuff will be completely unable to sort the wheat from the chaff from an anonymous online forum.
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IIRC each of the pilots flying initially gave up more ground to MCAS ANU stab movement than did the pilots who followed them. Thus each of those pilots upon taking control started in a deep hole that much closer to a literal vertical plummet if they let the trim run for too long, and the starting position of the trim when they took control was not basically neutral, but roughly halfway to the stops, meaning they were fighting far heavier control column forces from the first moment of control.
The ET302 flight was a whole different situation. The Captain got behind the trim and stayed behind until impact.
So again, what was the difference in the training, experience, and/or environment of the first three pilots and the last two that may have explained the dramatic difference in performance? We don't have the information (at least yet), but it is a reasonable line of inquiry.
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I think the crew of the penultimate Lion Air 610 flight did a great job handling this emergency, particularly since at this point no one outside of Boeing had ever heard of MCAS. They dealt with the immediate stick shaker, recognize the plane was flying and not stalling, and identified the IAS DISAGREE problem early on. They were rightfully taken surprise by the MCAS event, but they kept the plane flying, both the Captain and FO in turn, while they tried to sort out the problem. They used the resources available to get the malfunction contained and eventually landed safely. Good job all round.
We can look at their performance and see it follows a pretty standard three-step approach to dealing with any aircraft emergency. Different airlines/flying organizations may express this process in different ways, but the version I prefer goes like this:
1. Maintain aircraft control
2. Evaluate the situation and take appropriate action
3. Land as soon as conditions permit
While each step is critical in its own right, it is important to note that you can’t get to Steps 2 or 3 without first getting through the critical Step 1. You can actually make mistakes or fail to complete Step 2 and still get through the situation. Step 3 is, of course, mandatory for successful completion.
I think the crew of the penultimate Lion Air 610 flight did a great job handling this emergency, particularly since at this point no one outside of Boeing had ever heard of MCAS. They dealt with the immediate stick shaker, recognize the plane was flying and not stalling, and identified the IAS DISAGREE problem early on. They were rightfully taken surprise by the MCAS event, but they kept the plane flying, both the Captain and FO in turn, while they tried to sort out the problem. They used the resources available to get the malfunction contained and eventually landed safely. Good job all round.
We can look at their performance and see it follows a pretty standard three-step approach to dealing with any aircraft emergency. Different airlines/flying organizations may express this process in different ways, but the version I prefer goes like this:
1. Maintain aircraft control
2. Evaluate the situation and take appropriate action
3. Land as soon as conditions permit
While each step is critical in its own right, it is important to note that you can’t get to Steps 2 or 3 without first getting through the critical Step 1. You can actually make mistakes or fail to complete Step 2 and still get through the situation. Step 3 is, of course, mandatory for successful completion.
- attempting to engage the autopilot twice with the stick shaker active and unreliable air speed and ALT disagree;
- some posters previously said that retracting flaps early in this situation is not a great idea either;
- fighting with MCAS for about 5 minutes before using the cutout switches;
- temporarily re-enabling electric trim 5 minutes later.
However I do have some actual criticism about their later actions during and after the flight:
- "Step 3 is, of course, mandatory" - then it's funny they skipped that step. Instead of landing "as soon as conditions permit" they kept flying to the destination, with the stick shaker active for over 90 minutes (unless they pulled its circuit breaker). In my opinion flying to the destination in a bird that was clearly very sick and repeatedly tried to kill them was not wise. Yes, "land as soon as possible" was missing from the checklists for the problems they experienced, but still, unless they were afraid their airline would punish them for not continuing the flight, I don't understand why they continued their flight to the destination. In my opinion they subjected their passengers to unnecessary risk.
- Post flight they reported: "Airspeed unreliable and ALT disagree shown after takeoff, STS also running to the wrong direction, suspected because of speed difference, identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree. Decide to continue flying to CGK at FL280, landed safely runway 25L.". They made no mention in their report that they had the stick shaker active for the entire flight, or that they had to use the cutout switches and had to trim manually with the trim wheels for most of the flight.
Including that additional information in their report could have given the technicians a chance to find the real problem, or at least it could have given the next crew enough information to be able to deal with the problem successfully. I find it very strange that they didn't include that in their report.
To conclude, sorry, but I can't agree that this was a great job.
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It will be very interesting to learn about the scenario in which the problem EASA has raised was discovered.
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Aren't they supposed to verify that Boeing have done their homework ?
On the other hand it might be encouraging that the FAA now calls some shots - their verifying hasn’t been too successful in the recent past...
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And yet those issues should have been managed during project reviews, fixed and tried and proven by Boeing and their own pilots, and all the paperwork cleared before the sim demonstration.
How come the FAA had to do the job ?
Looks as if Boeing are still at a loss as to what to do, what to fix, how to test their software. Din't they have had 8 months to (re)hire senior engineers to sort things out ?
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How about putting MCAS to rest and automatically set slats or flaps in any future MAX low speed scenario instead? Could this be a way around the stick feel requirements or must a clean approach to stall be demonstrated in any case? Before misusing trim I'd misuse the high lift stuff.
Last edited by Kerosene Kraut; 6th Jul 2019 at 19:11.
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Just wondering:
The stall warning stick shaker and MCAS were a direct result from (badly) realised systems but they were kind of correct though based on bad data.
The UAS warning was (apparently) false but the primary data -pitot pressure- was correct. It was calculated to false with bad secondary data (AoA). Now if the comparison had been on pitot pressures no warning would have occured?
What is the opinion on showing one or the other?
repost
The stall warning stick shaker and MCAS were a direct result from (badly) realised systems but they were kind of correct though based on bad data.
The UAS warning was (apparently) false but the primary data -pitot pressure- was correct. It was calculated to false with bad secondary data (AoA). Now if the comparison had been on pitot pressures no warning would have occured?
What is the opinion on showing one or the other?
repost
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I don't think there is an easy fix for that. But the difficulty in manually trimming is not unique to the Max - NG has the same issue above a certain airspeed.
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In a well managed company, there would have been a team working on a fix for months now, with the prototype hardware already test flown, and a production team poised for manufacturing retrofit kits by the thousand at short notice.
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Just wondering:
The stall warning stick shaker and MCAS were a direct result from (badly) realised systems but they were kind of correct though based on bad data.
The UAS warning was (apparently) false but the primary data -pitot pressure- was correct. It was calculated to false with bad secondary data (AoA). Now if the comparison had been on pitot pressures no warning would have occured?
What is the opinion on showing one or the other?
repost
The stall warning stick shaker and MCAS were a direct result from (badly) realised systems but they were kind of correct though based on bad data.
The UAS warning was (apparently) false but the primary data -pitot pressure- was correct. It was calculated to false with bad secondary data (AoA). Now if the comparison had been on pitot pressures no warning would have occured?
What is the opinion on showing one or the other?
repost
Perhaps an "uncorrected" warning with both displays reverting to raw speed, perhaps with an uncertainty band.
The difference being that UAS requires speeds to be treated as fully unreliable and not to be trusted.
Then again this might all just add another layer of complication for what should be an straightforward memory item.
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Including that additional information in their report could have given the technicians a chance to find the real problem, or at least it could have given the next crew enough information to be able to deal with the problem successfully. I find it very strange that they didn't include that in their report.
This really goes to the fact that Boeing chose not to document the existence of the MCAS system. The behavior that the pilots experienced was impossible in the NG so they used their best guess as to the cause, and as humans do, filtered out information that was irrelevant to the cause. After all, their job is to get from A to B and they are not trained in the art of system diagnosis and documentation. In fact, everything I have read here indicates that pilots are explicitly discouraged from failure diagnosis, which is the justification for why the function of the two cutout switches was changed. To now blame the pilots for an inadequate description of the failure seems contradictory.
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What I'm complaining about is not necessarily MAX / MCAS specific. I would still criticize them for not reporting the stick shaker even if they were flying an NG, not a MAX. Reporting the stick shaker running for 90 minutes would suggest to the technicians the issues could be related to the AoA vanes. They didn't do that, and in the AFML they put even less information:
- "IAS and ALT Disagree shown after take off"
- "feel diff press light illuminate"
As a result the engineers:
- "Performed flushing Left Pitot Air Data Module (ADM) and static ADM. Operation test on ground found satisfied."
- "performed cleaned electrical connector plug of elevator feel computer carried out. test on ground found OK."
The engineers did nothing about the AoA vane, as nothing in the pilot reports directly suggested an issue with the AoA vane.
Not sure why they didn't report the stick shaker. Maybe they were afraid to report that they have flown with the stick shaker active for 90 minutes. But in my opinion the end result is that they created another hole in the cheese for the next flight.
- "IAS and ALT Disagree shown after take off"
- "feel diff press light illuminate"
As a result the engineers:
- "Performed flushing Left Pitot Air Data Module (ADM) and static ADM. Operation test on ground found satisfied."
- "performed cleaned electrical connector plug of elevator feel computer carried out. test on ground found OK."
The engineers did nothing about the AoA vane, as nothing in the pilot reports directly suggested an issue with the AoA vane.
Not sure why they didn't report the stick shaker. Maybe they were afraid to report that they have flown with the stick shaker active for 90 minutes. But in my opinion the end result is that they created another hole in the cheese for the next flight.
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Except...that Boeing probably didn't know either. I seem to remember that the possibility of an AOA vane/signal failure had not been tested nor been part of an FMEA.
They had just provided the "just run the Stab Runaway procedure". Which had not been properly tested on the MAX.
Nobody knew what would happen in case of nuisance MCAS activation.
And considering their difficulties trying to fix things up, they might still not quite know...
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It is a bit odd to be blaming an aircrew in Ethiopia for not providing information that Boeing engineering already knew! Airline pilots are not supposed to be the testing and documentation department.
This really goes to the fact that Boeing chose not to document the existence of the MCAS system. The behavior that the pilots experienced was impossible in the NG so they used their best guess as to the cause, and as humans do, filtered out information that was irrelevant to the cause. After all, their job is to get from A to B and they are not trained in the art of system diagnosis and documentation. In fact, everything I have read here indicates that pilots are explicitly discouraged from failure diagnosis, which is the justification for why the function of the two cutout switches was changed. To now blame the pilots for an inadequate description of the failure seems contradictory.
This really goes to the fact that Boeing chose not to document the existence of the MCAS system. The behavior that the pilots experienced was impossible in the NG so they used their best guess as to the cause, and as humans do, filtered out information that was irrelevant to the cause. After all, their job is to get from A to B and they are not trained in the art of system diagnosis and documentation. In fact, everything I have read here indicates that pilots are explicitly discouraged from failure diagnosis, which is the justification for why the function of the two cutout switches was changed. To now blame the pilots for an inadequate description of the failure seems contradictory.
Given that that aircrews are discouraged from failure diagnoses it would have been better to report 'what happened' rather than speculate on system/cause "sts running backward", would have been much better logged as "recurring uncommanded severe nose down trim requiring use of trim cutout switches"
Anyone with tech support experience has likely had experience with a user who describes what is happening in terms of their guess as to cause rather than observed behavior. Not to say that a guess on cause is not useful at times but it should be distinct from the symptom report.
BTW: In much of the aviation world (outside USA) "engineer" refers to an aircraft mechanic, not someone who designs airplanes, not sure if this could have influenced your statement re providing information to Boeing Engineering.
Another thought is that had the broken (not an option) AOA disagree warning been functional on the penultimate Lion Air it would have likely been logged and also triggered maintenance rechecking of AOA sensors.
This annoys me everytime I see a spokesperson stating that it likely would not have affected the outcome, arguably possibly true for the accident flights but not the prior Lion Air flight.
Psychophysiological entity
2 events, one every 90,000 flights, versus millions of flights and 1 every 5,000,000. You are correct, regression to the mean cannot be ignored. But superficially it's pretty damning.
Both the EASA and the FAA don't seem to think it is a coincidence, and we can hope at least one of those bodies is independent and competent. They grounded the plane, not the pilots.
I think we all agree that the failure of AoA information was the prime cause. That loss, or corruption, of data was for two entirely different reasons. To me, that's an horrific coincidence in such a short timescale.
The prime cause has revealed other issues with the type in general, not just the MAX, several of them pretty serious. Frankly, I think Boeing have a far greater challenge than most people realise when we add the alarming company culture problems to the list of software and mechanical issues. Getting the aircraft back in the air is a multifaceted problem-solving battle. It's akin to being at war on several fronts.
Not a 737 engineer (mechanic) but the defect "sts running backwards" would be very alarming to me on the aircraft that I work on.
This especially as there is a trim cable and clutch in the system - I would have been contacting the captain for a detailed description.
This especially as there is a trim cable and clutch in the system - I would have been contacting the captain for a detailed description.