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> properly functioning (but awkward and confusing) MCAS systems It had almost unlimited pitch authority, used only one (potentially faulty) AOA indicator to de

> properly functioning (but awkward and confusing) MCAS systems It had almost unlimited pitch authority, used only one (potentially faulty) AOA indicator to decide to activate, and could activate repeatedly unless purposefully deactivated. Even the way in which it was certified was extremely suspect. I'm curious as to how you think that is "properly functioning". Its initial implementation was straight up dangerous, as should be plainly obvious by the 346 deaths it caused. (https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile...) In the cases of the Ethiopian crash, they _were_ aware of the "proper" procedure to deactivate the MCAS: > But on the Ethiopian Airlines flight, the pilots appear to have recognized the errant MCAS problem and flipped the cutoff switches as described in the checklist. But then it appears that the pilots were unable to move the manual wheel, likely because the forces on the tail made it physically challenging to turn. > The bottom of Boeing’s runaway stabilizer checklist seems to acknowledge the possibility of this physically challenging scenario. It suggests that the pilots can first use the electric trim to neutralize those potential forces before hitting the cutout switches. > After failing to manually control the stabilizer, the Ethiopian Airlines pilots appear to have flipped the cutoff switches back on, which awakened the MCAS system. It soon sent the plane diving to Earth. (https://www.seattletimes.com/business/boeing-aerospace/boeing-altered-key-switches-in-737-max-cockpit-limiting-ability-to-shut-off-mcas/ https://www.seattletimes.com/business/boeing-aerospace/boein...) They let their airspeed get too high, so they were unable to manually trim because of the physical forces involved. But making this mistake during this phase of flight this is somewhat understandable, as they encountered the problem just one minute after takeoff (which is a pretty critical / task heavy phase of flight) and were still very close to the ground. Chelsea Sullenberger (the guy who ditched into the Hudson) commented that "Even knowing what was going to happen, I could see how crews would have run out of time and altitude before they could have solved the problems." (https://www.bloomberg.com/news/articles/2019-06-20/fight-for-survival-on-doomed-jet-came-down-to-two-cockpit-wheels https://www.bloomberg.com/news/articles/2019-06-20/fight-for...) > Also, it was 2 crashes in 500,000 flights. It seems a little misleading to just compare it to hull losses. If we're talking about the relative safety of different aircraft, no it's not. Compared to, say, the Airbus A320neo (which has had 0 hull losses over ~1300 aircraft over 10 years), it's terrible. It's a far less safe plane.

WalterBright 6y ago
The EA pilots were given an Emergency Airworthiness Directive which gave a two step process for recovering from MCAS malfunction: 1. use the electric trim switches to drive the trim to normal 2. cut off the trim system with the console cutoff switches. That's it. As simple as that. And it is NOT what the EA pilots did (they cut off the trim first). Here are the exact directions: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... Why they didn't read, remember, or follow the EAD instructions is anybody's guess, as I've never heard of any investigation into that aspect.
- acqq 6y ago
  Thanks for giving the link to the document. Looking at the context, the sentence you quoted is more a built-in disclaimer than a procedure that the pilots were supposed to learn to apply in only a few seconds they would have before the airplane crashes to the ground for overriding pilot close to the ground. After all the changes, it's at the end, and uses the weaseling "may be needed" and "can be used". We saw that not doing very specific sequence in a few seconds makes the plane non steerable. Edit: Answering: "The LA pilots worked the problem for 5 minutes, the EA 2 minutes. Quite a bit more than seconds." They "worked the problem" during that time by actively attempting to prevent the plane to crash. It's surely not that they simply had that much time to think about what to do next. Also, during most of that time of "minutes", if I remember correctly, the plane was most of the time actively turning to the ground, overriding their attempts to force it flying in the safe direction and doing that repeatedly. I really don't see that for these two accidents it can be said that it was "a pilot error" and I don't see any institution claiming that publicly anymore, even if some would really, really like to be able to do that and would immediately do, if it were possible. "Two simple steps"? Well "may be needed" and "can be used" is surely not even "after X happens do P and then do Q, if not exactly done in that sequence and at that point, the plane will surely crash." Nobody had the training to fight against the program that every time they straightened the plane up turned it back to the ground, making the manual trim impossible to be applied.

WalterBright 6y ago

The EA pilots were given an Emergency Airworthiness Directive which gave a two step process for recovering from MCAS malfunction: 1. use the electric trim switches to drive the trim to normal 2. cut off the trim system with the console cutoff switches. That's it. As simple as that. And it is NOT what the EA pilots did (they cut off the trim first). Here are the exact directions: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... Why they didn't read, remember, or follow the EAD instructions is anybody's guess, as I've never heard of any investigation into that aspect.

acqq 6y ago
Thanks for giving the link to the document. Looking at the context, the sentence you quoted is more a built-in disclaimer than a procedure that the pilots were supposed to learn to apply in only a few seconds they would have before the airplane crashes to the ground for overriding pilot close to the ground. After all the changes, it's at the end, and uses the weaseling "may be needed" and "can be used". We saw that not doing very specific sequence in a few seconds makes the plane non steerable. Edit: Answering: "The LA pilots worked the problem for 5 minutes, the EA 2 minutes. Quite a bit more than seconds." They "worked the problem" during that time by actively attempting to prevent the plane to crash. It's surely not that they simply had that much time to think about what to do next. Also, during most of that time of "minutes", if I remember correctly, the plane was most of the time actively turning to the ground, overriding their attempts to force it flying in the safe direction and doing that repeatedly. I really don't see that for these two accidents it can be said that it was "a pilot error" and I don't see any institution claiming that publicly anymore, even if some would really, really like to be able to do that and would immediately do, if it were possible. "Two simple steps"? Well "may be needed" and "can be used" is surely not even "after X happens do P and then do Q, if not exactly done in that sequence and at that point, the plane will surely crash." Nobody had the training to fight against the program that every time they straightened the plane up turned it back to the ground, making the manual trim impossible to be applied.