7 ms·

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. The

"- 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.

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.