9 ms·

Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

158 points by xmichael0 6y ago

xmichael0 6y ago
- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS.
geocrasher 6y ago
"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." Indeed. This was a part failing on an aircraft in flight. It landed without incident, and was likely never in any sort of danger. Losing electric trim is an annoyance but also trims safety margins by, as I understand it, making autopilot impossible. So, it's good that they returned. If this had happened on a 767 or A320 we'd never have heard about it.
- berkut 6y ago
  With respect to the 737-8 MAX though, although in this case it's nothing to do with MCAS, doesn't the 737-8 MAX have smaller radius trim wheels than previous models (so less leverage)? So in theory, trimming might be more difficult on the MAX than previous 737 models, especially at higher speeds (where there's more force on the control surfaces that would need to be counteracted in the case of runaway trim).
  - slacktide 6y ago
    The trim wheel on the 737 MAX is identical, down to the part number, to the trim wheel on the 737 NG, which has been in service since 1997. The trim wheel on the 737 NG was reduced in diameter by approx 1/8 of an inch compared to the 737 Classic, which has been in service since 1982, in order to give adequate clearance to the “new” CDU (data entry keyboard for the flight management system). Since the trim wheel is around 10” in diameter, a 1/8” change would have a negligible effect on trim forces.
- jjtheblunt 6y ago
  Why re 767 or A320? (i'm guessing because they're not recently in the news.)
  - gfiorav 6y ago
    737 max had two fatal crashes due to automated trimming issues (MCAS) and the fleet had been grounded until very recently.
- andy_ppp 6y ago
  As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane?
  - na85 6y ago
    >As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). That's not really correct. The engines being in a different position means the aircraft doesn't meet a very specific criterion of the FARs (positive stick force gradient). The 737 Max has the exact same relationship with trim as any other airliner. >Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane? No. TFA explicitly states this issue was not related to MCAS. It's likely an analogous failure on an A320 or a 737NG would still have necessitated aborting the flight.
    - slacktide 6y ago
      One thing that has always bothered me about how MCAS was implemented - if it truly was a stick force gradient issue, why not make the change in the Elevator Differential Feel Computer, which already manipulates the stick force gradient during approach to stall, rather than physically moving a control surface? Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s.
      - bonzini 6y ago
        Maybe that's why, I don't blame engineers who didn't want to touch it...
      - salawat 6y ago
        >Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s. That's likely why they didn't. That type of change is hard to conceal and far more difficult to keep out of the documentation. A software change could potentially be handwaved. Full on revamping of said system would probably have edged a regulator enough to have raised an objection or a deeper dive into the nature of the reconfiguration.
- ulfw 6y ago
  It's a new aircraft not one 20years in service like your average 767 or A320!
  - TylerE 6y ago
    That makes it less surprising, not more. Component failures follow a bathtub curve. Mid-life is the lowest failure rate.
- martimarkov 6y ago
  I agree but it’s like the galaxy phone that had the battery issue. It just killed confidence with the consumer. The investigation (and what we learned form it) into Boeing also didn’t help with confidence levels. After a few new iterations nobody talks about the battery anymore. I’m not so sure how Boeing can turn this around relatively quickly.
  - HeWhoLurksLate 6y ago
    Speaking of which, I have a friend that still runs a Note7
    - fsckboy 6y ago
      weren't those banned from flying on 737MAX's? (and all other aircraft)
  - sharken 6y ago
    For starters they can reiterate what has been said here, that a common error occurred and not the original MCAS problem. Not being open about it will have the opposite effect.
  - jryle70 6y ago
    Southwest just placed a large order for 737MAX-7 two days ago - [0]. 100 firm orders plus 155 options. They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery. [0] - https://www.cnbc.com/2021/03/29/southwest-airlines-adds-100-orders-for-boeing-737-max-jet.html https://www.cnbc.com/2021/03/29/southwest-airlines-adds-100-... Meta note, this relatively frequent aircraft incident gets a lot of votes here on HN, yet the Southwest's order falls off the crack. Objectivity is as scarce on HN as on any other media frequently criticized here.
    - rualca 6y ago
      > They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery. Is this supposed to mean anything? To me it reads like an airline managed to get a massive discount on inventory that a struggling aircraft manufacturer hasn't been able to move for about a year due to their repeated problems with safety and accountability, which led the whole world to drop their orders.
- phire 6y ago
  Not just the autopilot, but if pitch trim has failed then the Speed Trim System is disabled too. What is Speed Trim? Well imagine MCAS, but instead of moving the stabiliser near the edge of the flight envelope, it moves the stabiliser all the time (when the speed is below mach 0.68). And instead of being introduced with the 737 Max, it was introduced 35 years ago with the 737 classic. At least it's mentioned in the manual.
benmarten 6y ago
I'm refusing to fly the MAX, period! The plane is flawed by design...
- airhead969 6y ago
  I have no opinion about flying on this particular plane. It's not so much MCAS, electric trim, this, or that. The bigger issue is it's too complicated, has too many features, and the FAA can't adequately oversee testing and certification all the way down the engineering stack. Furthermore, because of pressures to save a buck, Boeing is willing to cut corners and sacrifice safety by slapping a plane together without properly engineering or testing it. Because of this behavior, it's difficult to know how many other problems are lurking around like in the 787.
  - worker767424 6y ago
    This is every commercial plane, though. We've traded more frequent crashes due to human error for fewer, more spectacular crashes due to how complex planes have become.
    - airhead969 6y ago
      False equivalency and hasty generalization that equivocates every plane as having the same risks when they clearly don't, and ignoring testing and training process improvements. Also, an oversimplification that somehow fundamentals of aviation are shifted as a finite resource over to automation when that's clearly not the case. 737 classics are simpler and reliable. The NG's randomly have hidden structural weaknesses exposed during runway overruns and hard landings when the fuselage breaks up because of Ducommun and Boeing negligence. The MAX is a steaming pile that may be a white elephant around Boeing's neck. The 787 is notoriously-bad. The 777 is pretty good. Airbus has had much more automation for years. Are they dropping out of the sky? Maybe they manage their complexity better than Boeing, who hires underpaid engineers to work on things that they're really not qualified to do.
      - 6y ago
i_work_at_GOOG 6y ago
Guys, this is a very common and well-known problem. It's been around for over 4 years now. The good news is that instead of nosediving into the ground the 737s can now land and be swapped out. The main take away here is that there are no more fatal crashes. This is a solid improvement for Boeing.
- airhead969 6y ago
  I wonder if people realize it's sarcasm. Nope. - Poe's law
  - scrollaway 6y ago
    How about scrollaway's law of post quality: if your sarcastic post sounds believable enough for Poe's law, it's a shitty post no matter how it's interpreted.
    - airhead969 6y ago
      Sounds believable to whom? You're assuming an absolutist perspective of inference. Sarcasm's law: without a tell, it doesn't always come across as sarcasm without common sense. The latter is often missing these days, hence Poe's law. internet's law: The average level of common sense, intelligence, sense of humor, benefit-of-the-doubt, and decency decays over time. airhead's law: Quality sarcasm poetically-highlights an insight rather than ejaculates (meaning no. 2) a humorous quip.
    - ergl 6y ago
      In more profane terms: https://news.ycombinator.com/item?id=17733579 https://news.ycombinator.com/item?id=17733579
eric4smith 6y ago
I sympathize with the engineers there. It's like a bug that will not go away in some software. You think you've fixed it and all seems well and you get a good nights sleep with the gleam of satisfaction in your eyes. But the next day your manager says "That bug is still there". You incredulously do not believe that bug report and go to replicate it yourself. And surely, under some edge weird case scenario, it really happened. You put the fix in and uneasily sleep the next night. You actually dreamed about the issue. And wake the morning with no reports. Over the next weeks and months, its all good. No new reports. and your mind has turned to some new projects. Surely that bug has been squashed. And then one day... I feel their pain. It's not the same, because lives and reputations are at stake. It's so much worse.But I feel their pain.
- na85 6y ago
  Aerospace engineer here. From TFA: >A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS. That statement is from the airline, not from Boeing, so I'm more inclined to trust it. Additionally, if the airline lies and it turns up on an airworthiness audit (air maintenance organizations are subject to regular audits) then the penalties are quite severe. In any case, per the airline's statement it was an issue unrelated to MCAS. Aircraft break literally every day in a myriad of ways that are often invisible/imperceptible to people riding on that very aircraft. In this particular case it was some unspecified component of the electric trim system. You can look up the Master Minimum Equipment List for the B737[0] and see for yourself just how granular the approved maintenance program gets for aircraft like this. Everything on the MMEL is essentially an item that can be broken and the aircraft can still take off legally. Note that this is a different (and more rigorous) standard than "can be broken and aircraft can take off/operate safely". I don't know exactly what broke here but I suspect it is a part that has broken on 737s hundreds if not thousands of times in the past, with similar outcomes. I merely dabble in software but to further your analogy: This situation is when you've been dreaming about that bug for weeks and you get the call from the boss thinking it has recurred but instead it turns out it was a similar-smelling failure caused by some intern's microservice not failing gracefully when confronted with a network outage that brought down the system anyways. [0] https://fsims.faa.gov/wdocs/mmel/b-737%20r55a.htm https://fsims.faa.gov/wdocs/mmel/b-737%20r55a.htm
technick 6y ago
I flew on one of the returned 737-max aircraft down to Houston about a month ago. Flight was uneventful and landed a few minutes early.
- airhead969 6y ago
  Anecdotal evidence but glad you survived.
- spoonjim 6y ago
  Thankfully, our standards for aviation safety are not low enough for an anecdote of a safe landing to be a valuable data point.
stryker7001 6y ago
So if the situation came, where the plane was at the edge of its flight envelope and needed to use MCAS (or whatever its called now), it wouldn't have been able to use it, causing the plane to stall? Thats a lot more serious then.
- slacktide 6y ago
  Nope. “The EASA flight tests confirmed that MCAS was needed to provide full compliance but also that the loss of this function does not preclude the safe flight and landing of the aircraft; i.e. the 737 MAX remains stable following the loss of the MCAS function.” https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_Return_to_Service_Report.pdf https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_...
- Toutouxc 6y ago
  The plane doesn't really NEED to use MCAS. Systems like MCAS or Speed Trim and others do not make the planes flyable, they make them predictable. Aerodynamically, even the 747 or the A380 are normal planes operating on the same principles as the tiny Cessna 172, they're just much bigger, fly faster and react a lot slower. Airliners are packed with systems that make them dull and predictable to fly, because things can break on a sunny day over Texas, but also at midnight in the rain over the Atlantic, and the last thing you want your pilots to care about when they're stressed out, disoriented and working through complicated checklists is whether this particular plane has a weird tendency to pitch up at these particular conditions.
BenoitP 6y ago
"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." I don't get it. It is common for other airliners to rely systematically on trimming? Do other airliners have similar 'correcting' systems as MCAS?
- airhead969 6y ago
  Yeap. The electric trim systems tend to be automatic with speed and altitude to approximate what the pilot wants via trim up/down controls. Without trim, planes would be pitching and diving all over the place, or at least require yoke/sidestick back-pressure to hold steady. Some planes can be trimmed through enormous deflections of the horizontal stabilizer. If configured incorrectly and under the wrong conditions, incorrect trim can lead to dangerous flight characteristics like pitching up or down beyond what the elevators can handle at full deflection. A broken jackscrew (part that moves the horizontal stabilizer for the trim commands) can cause this type of dangerous configuration or even worse.
- dghlsakjg 6y ago
  Almost every airplane except the absolute most basic have trim controls for flight surfaces, especially the elevator. Even little two seat Cessnas get trim controls. Trim is changed for each phase of flight. Electric trim is just a motor spinning the manual trim control. Most airliners will be doing constant trim adjustment. If you want a real change of pace check out Airbus’ control system. It does a lot more intervention than anything Boeing does. Depending on the state of the aircraft the control stick will respond to input in entirely different ways (3 ‘laws’ that contain no less than 5 submodes). Sometimes it will act as you would expect a stick to act, other times it will intentionally limit what the pilot is asking of the plane, sometimes it will average what the two pilots are asking. Confusion about how the system works has caused at least two crashes I can think of (AF447, QZ8501). It’s killed more people than the Max, but it was written off as pilot error since it was operating as designed in both cases. It just happens to be a design that will change the way the plane is controlled when things go wrong. A few of the modes do in fact include automatic trim adjustments.
rurban 6y ago
Just a loose cord, ha!
kdtop3 6y ago
Did this happen to be anywhere in the Bermuda triangle? :-)
qubit000 6y ago
Boeing has lost the public trust not only in the US, but internationally. Inherent instability aside, fact remains the general perception is that Boeing retrofitted engines too large for 50yr plane design necessitating structural modifications which compromised its flight worthiness. As a result, software had to be written to compensate for this, which unbelievably, relied on input from a single sensor--iow, single point of failure. The lost of trust is further exacerbated by the fact that Boeing/FAA knew there was high probability of another crash after the first catastrophic incident but refused to ground the planes continuing to let them fly while issuing deceptive public statements regarding the planes safety. Boeing's largest market is China, which justifiably, will not allow the 737 to fly within their territory.
- hnarn 6y ago
  What has really ruined my trust for Boeing is not necessarily the incidents with the 737 MAX model specifically, but more the change in that company's culture that these incidents have made me aware of. I can recommend this video[1], but the short of it seems to be that Boeing over a period of decades has replaced its previous "engineering first" culture with what I can only describe, for lack of better wording, as the "suits taking over", with predictable results. [1]: https://www.youtube.com/watch?v=y_zn_x2JK5Q https://www.youtube.com/watch?v=y_zn_x2JK5Q
- slacktide 6y ago
  Boeing did not get into this position overnight. After the massive cost and schedule overruns on the 787 program, they were far too cash-poor to fund the development of a clean-sheet design, hence the re-warmed 737. The 787 itself was a huge experiment in outsourcing both the costs and risks of aircraft development. It turns out you can outsource cost, but the prime contractor always owns the risk. Dr. John Hart-Smith published an excellent white paper warning of this while the precursor to the 787 was still in development, shortly after the Boeing-McDonnell Douglass merger. https://www.google.com/search?q=Outsourced+Profits+%E2%80%93+The+Cornerstone+of+Successful+Subcontracting https://www.google.com/search?q=Outsourced+Profits+%E2%80%93...

158 points by xmichael0 6y ago

- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS.

geocrasher 6y ago

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." Indeed. This was a part failing on an aircraft in flight. It landed without incident, and was likely never in any sort of danger. Losing electric trim is an annoyance but also trims safety margins by, as I understand it, making autopilot impossible. So, it's good that they returned. If this had happened on a 767 or A320 we'd never have heard about it.

berkut 6y ago
With respect to the 737-8 MAX though, although in this case it's nothing to do with MCAS, doesn't the 737-8 MAX have smaller radius trim wheels than previous models (so less leverage)? So in theory, trimming might be more difficult on the MAX than previous 737 models, especially at higher speeds (where there's more force on the control surfaces that would need to be counteracted in the case of runaway trim).
- slacktide 6y ago
  The trim wheel on the 737 MAX is identical, down to the part number, to the trim wheel on the 737 NG, which has been in service since 1997. The trim wheel on the 737 NG was reduced in diameter by approx 1/8 of an inch compared to the 737 Classic, which has been in service since 1982, in order to give adequate clearance to the “new” CDU (data entry keyboard for the flight management system). Since the trim wheel is around 10” in diameter, a 1/8” change would have a negligible effect on trim forces.
jjtheblunt 6y ago
Why re 767 or A320? (i'm guessing because they're not recently in the news.)
- gfiorav 6y ago
  737 max had two fatal crashes due to automated trimming issues (MCAS) and the fleet had been grounded until very recently.
andy_ppp 6y ago
As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane?
- na85 6y ago
  >As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). That's not really correct. The engines being in a different position means the aircraft doesn't meet a very specific criterion of the FARs (positive stick force gradient). The 737 Max has the exact same relationship with trim as any other airliner. >Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane? No. TFA explicitly states this issue was not related to MCAS. It's likely an analogous failure on an A320 or a 737NG would still have necessitated aborting the flight.
  - slacktide 6y ago
    One thing that has always bothered me about how MCAS was implemented - if it truly was a stick force gradient issue, why not make the change in the Elevator Differential Feel Computer, which already manipulates the stick force gradient during approach to stall, rather than physically moving a control surface? Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s.
    - bonzini 6y ago
      Maybe that's why, I don't blame engineers who didn't want to touch it...
    - salawat 6y ago
      >Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s. That's likely why they didn't. That type of change is hard to conceal and far more difficult to keep out of the documentation. A software change could potentially be handwaved. Full on revamping of said system would probably have edged a regulator enough to have raised an objection or a deeper dive into the nature of the reconfiguration.
ulfw 6y ago
It's a new aircraft not one 20years in service like your average 767 or A320!
- TylerE 6y ago
  That makes it less surprising, not more. Component failures follow a bathtub curve. Mid-life is the lowest failure rate.
martimarkov 6y ago
I agree but it’s like the galaxy phone that had the battery issue. It just killed confidence with the consumer. The investigation (and what we learned form it) into Boeing also didn’t help with confidence levels. After a few new iterations nobody talks about the battery anymore. I’m not so sure how Boeing can turn this around relatively quickly.
- HeWhoLurksLate 6y ago
  Speaking of which, I have a friend that still runs a Note7
  - fsckboy 6y ago
    weren't those banned from flying on 737MAX's? (and all other aircraft)
- sharken 6y ago
  For starters they can reiterate what has been said here, that a common error occurred and not the original MCAS problem. Not being open about it will have the opposite effect.
- jryle70 6y ago
  Southwest just placed a large order for 737MAX-7 two days ago - [0]. 100 firm orders plus 155 options. They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery. [0] - https://www.cnbc.com/2021/03/29/southwest-airlines-adds-100-orders-for-boeing-737-max-jet.html https://www.cnbc.com/2021/03/29/southwest-airlines-adds-100-... Meta note, this relatively frequent aircraft incident gets a lot of votes here on HN, yet the Southwest's order falls off the crack. Objectivity is as scarce on HN as on any other media frequently criticized here.
  - rualca 6y ago
    > They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery. Is this supposed to mean anything? To me it reads like an airline managed to get a massive discount on inventory that a struggling aircraft manufacturer hasn't been able to move for about a year due to their repeated problems with safety and accountability, which led the whole world to drop their orders.
phire 6y ago
Not just the autopilot, but if pitch trim has failed then the Speed Trim System is disabled too. What is Speed Trim? Well imagine MCAS, but instead of moving the stabiliser near the edge of the flight envelope, it moves the stabiliser all the time (when the speed is below mach 0.68). And instead of being introduced with the 737 Max, it was introduced 35 years ago with the 737 classic. At least it's mentioned in the manual.

benmarten 6y ago

I'm refusing to fly the MAX, period! The plane is flawed by design...

airhead969 6y ago
I have no opinion about flying on this particular plane. It's not so much MCAS, electric trim, this, or that. The bigger issue is it's too complicated, has too many features, and the FAA can't adequately oversee testing and certification all the way down the engineering stack. Furthermore, because of pressures to save a buck, Boeing is willing to cut corners and sacrifice safety by slapping a plane together without properly engineering or testing it. Because of this behavior, it's difficult to know how many other problems are lurking around like in the 787.
- worker767424 6y ago
  This is every commercial plane, though. We've traded more frequent crashes due to human error for fewer, more spectacular crashes due to how complex planes have become.
  - airhead969 6y ago
    False equivalency and hasty generalization that equivocates every plane as having the same risks when they clearly don't, and ignoring testing and training process improvements. Also, an oversimplification that somehow fundamentals of aviation are shifted as a finite resource over to automation when that's clearly not the case. 737 classics are simpler and reliable. The NG's randomly have hidden structural weaknesses exposed during runway overruns and hard landings when the fuselage breaks up because of Ducommun and Boeing negligence. The MAX is a steaming pile that may be a white elephant around Boeing's neck. The 787 is notoriously-bad. The 777 is pretty good. Airbus has had much more automation for years. Are they dropping out of the sky? Maybe they manage their complexity better than Boeing, who hires underpaid engineers to work on things that they're really not qualified to do.
    - 6y ago

i_work_at_GOOG 6y ago

Guys, this is a very common and well-known problem. It's been around for over 4 years now. The good news is that instead of nosediving into the ground the 737s can now land and be swapped out. The main take away here is that there are no more fatal crashes. This is a solid improvement for Boeing.

airhead969 6y ago
I wonder if people realize it's sarcasm. Nope. - Poe's law
- scrollaway 6y ago
  How about scrollaway's law of post quality: if your sarcastic post sounds believable enough for Poe's law, it's a shitty post no matter how it's interpreted.
  - airhead969 6y ago
    Sounds believable to whom? You're assuming an absolutist perspective of inference. Sarcasm's law: without a tell, it doesn't always come across as sarcasm without common sense. The latter is often missing these days, hence Poe's law. internet's law: The average level of common sense, intelligence, sense of humor, benefit-of-the-doubt, and decency decays over time. airhead's law: Quality sarcasm poetically-highlights an insight rather than ejaculates (meaning no. 2) a humorous quip.
  - ergl 6y ago
    In more profane terms: https://news.ycombinator.com/item?id=17733579 https://news.ycombinator.com/item?id=17733579

eric4smith 6y ago

I sympathize with the engineers there. It's like a bug that will not go away in some software. You think you've fixed it and all seems well and you get a good nights sleep with the gleam of satisfaction in your eyes. But the next day your manager says "That bug is still there". You incredulously do not believe that bug report and go to replicate it yourself. And surely, under some edge weird case scenario, it really happened. You put the fix in and uneasily sleep the next night. You actually dreamed about the issue. And wake the morning with no reports. Over the next weeks and months, its all good. No new reports. and your mind has turned to some new projects. Surely that bug has been squashed. And then one day... I feel their pain. It's not the same, because lives and reputations are at stake. It's so much worse.But I feel their pain.

na85 6y ago
Aerospace engineer here. From TFA: >A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS. That statement is from the airline, not from Boeing, so I'm more inclined to trust it. Additionally, if the airline lies and it turns up on an airworthiness audit (air maintenance organizations are subject to regular audits) then the penalties are quite severe. In any case, per the airline's statement it was an issue unrelated to MCAS. Aircraft break literally every day in a myriad of ways that are often invisible/imperceptible to people riding on that very aircraft. In this particular case it was some unspecified component of the electric trim system. You can look up the Master Minimum Equipment List for the B737[0] and see for yourself just how granular the approved maintenance program gets for aircraft like this. Everything on the MMEL is essentially an item that can be broken and the aircraft can still take off legally. Note that this is a different (and more rigorous) standard than "can be broken and aircraft can take off/operate safely". I don't know exactly what broke here but I suspect it is a part that has broken on 737s hundreds if not thousands of times in the past, with similar outcomes. I merely dabble in software but to further your analogy: This situation is when you've been dreaming about that bug for weeks and you get the call from the boss thinking it has recurred but instead it turns out it was a similar-smelling failure caused by some intern's microservice not failing gracefully when confronted with a network outage that brought down the system anyways. [0] https://fsims.faa.gov/wdocs/mmel/b-737%20r55a.htm https://fsims.faa.gov/wdocs/mmel/b-737%20r55a.htm

technick 6y ago

I flew on one of the returned 737-max aircraft down to Houston about a month ago. Flight was uneventful and landed a few minutes early.

airhead969 6y ago
Anecdotal evidence but glad you survived.
spoonjim 6y ago
Thankfully, our standards for aviation safety are not low enough for an anecdote of a safe landing to be a valuable data point.

stryker7001 6y ago

So if the situation came, where the plane was at the edge of its flight envelope and needed to use MCAS (or whatever its called now), it wouldn't have been able to use it, causing the plane to stall? Thats a lot more serious then.

slacktide 6y ago
Nope. “The EASA flight tests confirmed that MCAS was needed to provide full compliance but also that the loss of this function does not preclude the safe flight and landing of the aircraft; i.e. the 737 MAX remains stable following the loss of the MCAS function.” https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_Return_to_Service_Report.pdf https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_...
Toutouxc 6y ago
The plane doesn't really NEED to use MCAS. Systems like MCAS or Speed Trim and others do not make the planes flyable, they make them predictable. Aerodynamically, even the 747 or the A380 are normal planes operating on the same principles as the tiny Cessna 172, they're just much bigger, fly faster and react a lot slower. Airliners are packed with systems that make them dull and predictable to fly, because things can break on a sunny day over Texas, but also at midnight in the rain over the Atlantic, and the last thing you want your pilots to care about when they're stressed out, disoriented and working through complicated checklists is whether this particular plane has a weird tendency to pitch up at these particular conditions.

BenoitP 6y ago

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." I don't get it. It is common for other airliners to rely systematically on trimming? Do other airliners have similar 'correcting' systems as MCAS?

airhead969 6y ago
Yeap. The electric trim systems tend to be automatic with speed and altitude to approximate what the pilot wants via trim up/down controls. Without trim, planes would be pitching and diving all over the place, or at least require yoke/sidestick back-pressure to hold steady. Some planes can be trimmed through enormous deflections of the horizontal stabilizer. If configured incorrectly and under the wrong conditions, incorrect trim can lead to dangerous flight characteristics like pitching up or down beyond what the elevators can handle at full deflection. A broken jackscrew (part that moves the horizontal stabilizer for the trim commands) can cause this type of dangerous configuration or even worse.
dghlsakjg 6y ago
Almost every airplane except the absolute most basic have trim controls for flight surfaces, especially the elevator. Even little two seat Cessnas get trim controls. Trim is changed for each phase of flight. Electric trim is just a motor spinning the manual trim control. Most airliners will be doing constant trim adjustment. If you want a real change of pace check out Airbus’ control system. It does a lot more intervention than anything Boeing does. Depending on the state of the aircraft the control stick will respond to input in entirely different ways (3 ‘laws’ that contain no less than 5 submodes). Sometimes it will act as you would expect a stick to act, other times it will intentionally limit what the pilot is asking of the plane, sometimes it will average what the two pilots are asking. Confusion about how the system works has caused at least two crashes I can think of (AF447, QZ8501). It’s killed more people than the Max, but it was written off as pilot error since it was operating as designed in both cases. It just happens to be a design that will change the way the plane is controlled when things go wrong. A few of the modes do in fact include automatic trim adjustments.

rurban 6y ago

Just a loose cord, ha!

kdtop3 6y ago

Did this happen to be anywhere in the Bermuda triangle? :-)

qubit000 6y ago

Boeing has lost the public trust not only in the US, but internationally. Inherent instability aside, fact remains the general perception is that Boeing retrofitted engines too large for 50yr plane design necessitating structural modifications which compromised its flight worthiness. As a result, software had to be written to compensate for this, which unbelievably, relied on input from a single sensor--iow, single point of failure. The lost of trust is further exacerbated by the fact that Boeing/FAA knew there was high probability of another crash after the first catastrophic incident but refused to ground the planes continuing to let them fly while issuing deceptive public statements regarding the planes safety. Boeing's largest market is China, which justifiably, will not allow the 737 to fly within their territory.

hnarn 6y ago
What has really ruined my trust for Boeing is not necessarily the incidents with the 737 MAX model specifically, but more the change in that company's culture that these incidents have made me aware of. I can recommend this video[1], but the short of it seems to be that Boeing over a period of decades has replaced its previous "engineering first" culture with what I can only describe, for lack of better wording, as the "suits taking over", with predictable results. [1]: https://www.youtube.com/watch?v=y_zn_x2JK5Q https://www.youtube.com/watch?v=y_zn_x2JK5Q
slacktide 6y ago
Boeing did not get into this position overnight. After the massive cost and schedule overruns on the 787 program, they were far too cash-poor to fund the development of a clean-sheet design, hence the re-warmed 737. The 787 itself was a huge experiment in outsourcing both the costs and risks of aircraft development. It turns out you can outsource cost, but the prime contractor always owns the risk. Dr. John Hart-Smith published an excellent white paper warning of this while the precursor to the 787 was still in development, shortly after the Boeing-McDonnell Douglass merger. https://www.google.com/search?q=Outsourced+Profits+%E2%80%93+The+Cornerstone+of+Successful+Subcontracting https://www.google.com/search?q=Outsourced+Profits+%E2%80%93...