3 ms·

> Which is all to say that I think they likely have two separate AoA sensors. Correct, the 737 NG has two separate alpha vanes[1] and I believe the MAX does as

> Which is all to say that I think they likely have two separate AoA sensors. Correct, the 737 NG has two separate alpha vanes[1] and I believe the MAX does as well. However the "alpha vanes disagree" alert is a paid option per the emergency AD. Likewise the AoA indicator is a paid option. There is redundancy, but the plane may be configured such that the pilot cannot determine if there is a failure. Failure of one or both alpha vanes on an NG isn't a good thing, but failure of an alpha vane on a MAX could cause MCAS to essentially try to kill you and without that AoA disagree alert you may not know why because you've never been informed about this system, and at low altitude you likely wouldn't have time to figure out what's going on. Edit: if that all sounds fucking insane, it is. That's why American and Southwest pilot unions are livid[2]. 1: https://www.faa.gov/air_traffic/separation_standards/ase/2016_Event/documents/2.5_B737_Design_Differences.pdf https://www.faa.gov/air_traffic/separation_standards/ase/201... 2: https://www.seattletimes.com/business/boeing-aerospace/u-s-pilots-flying-737-max-werent-told-about-new-automatic-systems-change-linked-to-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/u-s-p...

ahartmetz 8y ago
Okay, so Boeing added an electronic safety feature (with a deadly failure mode) necessitated by physical changes and regulation. They didn't mention it for marketing reasons. They made an indicator of the deadly failure mode of the feature a paid option. Got it.
- VBprogrammer 8y ago
  Reading a little between the lines this is probably related to the pitch - power coupling present on all modern airliners. This is due to the thrust line being below the centre of lift meaning that increasing power causes a pitch up moment. In the 737 Max this probably got exacerbated to the point that it was possible to fly the plane into a stall by sharply increasing power in a high AoA situation (typically in a go-around). This was probably different enough to the 737NG that they felt it necessary to add the MCAS system to prevent having to do, what they considered, excessive differences training in that phase of flight.
  - FabHK 8y ago
    Could well be; I read somewhere that it was related to the ever bigger engines (for more efficient (higher) bypass ratio), which presumably have a lower centre of thrust.
    - VBprogrammer 8y ago
      They lengthened the nose gear 20cm to fit the new engines with the same ground clearance. Must have dropped the thrust centre line nearly half of that.
      - inferiorhuman 8y ago
        Well the Seattle Times quoted an ex-Boeing employee thusly: > A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily. > He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.
- notyourday 8y ago
  It is too bloody bad these people aren't being charged. They should go to jail, preferably in Indonesia.
FabHK 8y ago
> That's why American and Southwest pilot unions are livid[2] Wow, the information in that Seattle Times article is really damning! Differences training from the 737 NG to the MAX consisted of a one hour iPad session (plus crosswind training because the permissible roll is reduced due to vertical wing tips). Livid indeed.
- bronco21016 8y ago
  That’s actually incredibly common in the airline world. The issue isn’t so much the delivery method but more that information was withheld entirely. A brief description of this system allowing enough operational knowledge to be safe would only add a few minutes to the same iPad training.
Serow225 8y ago
I can't believe that the AoA disagree warning is a PAID option. And I've worked in aerospace.
- sjm-lbm 8y ago
  There's actually some precedent for this happening: AA flight 191, a DC-10 that crashed in 1979, wasn't equipped with two stick shakers (a stall warning device) - a paid option at the time. The series of events that caused the accident are a long story, but power was knocked out to the pilot's controls (where the one stick shaker was installed), but not the copilot's controls (which didn't have a stick shaker due to the selected options). TBH, it's doubtful that the pilots could have recovered in that specific situation, but the chances of success dropped to basically zero when they didn't have a device capable of communicating what was happening to them in time. Of course, this is obviously different than having no warning system for the type of failure whatsoever (as appears to be the case on the MAX), but it was still a little surprising for me.
  - Serow225 8y ago
    Good info thanks. But yeah, with a stick shaker there are many other ways for the pilots to get the same info, so I can sort of understand that as being optional for the copilot. Obviously not ideal, but at the end of the day engineering is nothing but compromise management :)

ahartmetz 8y ago

Okay, so Boeing added an electronic safety feature (with a deadly failure mode) necessitated by physical changes and regulation. They didn't mention it for marketing reasons. They made an indicator of the deadly failure mode of the feature a paid option. Got it.

VBprogrammer 8y ago
Reading a little between the lines this is probably related to the pitch - power coupling present on all modern airliners. This is due to the thrust line being below the centre of lift meaning that increasing power causes a pitch up moment. In the 737 Max this probably got exacerbated to the point that it was possible to fly the plane into a stall by sharply increasing power in a high AoA situation (typically in a go-around). This was probably different enough to the 737NG that they felt it necessary to add the MCAS system to prevent having to do, what they considered, excessive differences training in that phase of flight.
- FabHK 8y ago
  Could well be; I read somewhere that it was related to the ever bigger engines (for more efficient (higher) bypass ratio), which presumably have a lower centre of thrust.
  - VBprogrammer 8y ago
    They lengthened the nose gear 20cm to fit the new engines with the same ground clearance. Must have dropped the thrust centre line nearly half of that.
    - inferiorhuman 8y ago
      Well the Seattle Times quoted an ex-Boeing employee thusly: > A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily. > He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.
notyourday 8y ago
It is too bloody bad these people aren't being charged. They should go to jail, preferably in Indonesia.

FabHK 8y ago

> That's why American and Southwest pilot unions are livid[2] Wow, the information in that Seattle Times article is really damning! Differences training from the 737 NG to the MAX consisted of a one hour iPad session (plus crosswind training because the permissible roll is reduced due to vertical wing tips). Livid indeed.

bronco21016 8y ago
That’s actually incredibly common in the airline world. The issue isn’t so much the delivery method but more that information was withheld entirely. A brief description of this system allowing enough operational knowledge to be safe would only add a few minutes to the same iPad training.

Serow225 8y ago

I can't believe that the AoA disagree warning is a PAID option. And I've worked in aerospace.

sjm-lbm 8y ago
There's actually some precedent for this happening: AA flight 191, a DC-10 that crashed in 1979, wasn't equipped with two stick shakers (a stall warning device) - a paid option at the time. The series of events that caused the accident are a long story, but power was knocked out to the pilot's controls (where the one stick shaker was installed), but not the copilot's controls (which didn't have a stick shaker due to the selected options). TBH, it's doubtful that the pilots could have recovered in that specific situation, but the chances of success dropped to basically zero when they didn't have a device capable of communicating what was happening to them in time. Of course, this is obviously different than having no warning system for the type of failure whatsoever (as appears to be the case on the MAX), but it was still a little surprising for me.
- Serow225 8y ago
  Good info thanks. But yeah, with a stick shaker there are many other ways for the pilots to get the same info, so I can sort of understand that as being optional for the copilot. Obviously not ideal, but at the end of the day engineering is nothing but compromise management :)