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I was waiting to hear something like this. Generally speaking, Airline pilots who actually flew the plane are one of the best sources to consult when it comes t

I was waiting to hear something like this. Generally speaking, Airline pilots who actually flew the plane are one of the best sources to consult when it comes to determining any possible safety malfunction of an aircraft. One thing to note is the mention of a "Runaway Trim Checklist". When piloting an airliner, there is a checklist for almost everything. Sometimes there are multiple checklists with branching paths. Most emergency/malfunction checklists involve what are called "memory items". These are checklist steps that the pilot must remember in order to react quickly to any possible problem. After the memory items are completed, the pilots will break out the checklist binder and follow the checklist procedure that comes after the memory items. Every procedure the pilots undergo has passenger safety as it's #1 concern. Pilots are free to make whatever decision they deem necessary to ensure the safety of their passengers, even at the detriment of the airline's bottom line. They are free to make these decisions without question, even if the problem seems small. I believe it's important to note the above information whenever we look at these horrible accidents and try to reason about them. Often, pilots are the first line of defense against failures. Most aircraft have 2-3 redundant systems for almost every control and feature. Pilots need to understand and know how to work with and around these systems in order to react to emergency situations. That's why I think the MCAS isn't really to blame here as much as Boeing is to blame for not properly documenting it's operation in their manuals.

tim333 8y ago
>That's why I think the MCAS isn't really to blame here as much as Boeing is to blame for not properly documenting... I pretty sure the Ethiopian pilots would have been aware of the Lion Air crash and MCAS issues. The fact they still crashed suggests there's more to it.
- dragontamer 8y ago
  I think a wait-and-see approach is best (now that the planes are grounded). The black-box of the Ethiopian crash surely has the voice-recordings of the cockpit. So we'll be able to hear what the pilots were saying as the crash went down... we just gotta wait for the data. No point speculating when hard data is just around the corner. With the planes being grounded, there shouldn't be any safety issues if we wait.
outworlder 8y ago
> One thing to note is the mention of a "Runaway Trim Checklist". The pilots may not have recognized (in time) that it was a runaway trim issue. Many such issues involve trim being continuously applied. The trim wheel spins wildly. MCAS will trim in increments of 10s. So it will trim, pause, trim some more, pause. This may have confused the pilots. And they don't have much time to begin with – MCAS engages with autopilot off and flaps retracted. Most takeoffs have at least minimum flaps, so the plane will fly fine and then start misbehaving while still relatively close to the ground. > Most aircraft have 2-3 redundant systems for almost every control and feature. Yes. MAX 8 has two AOA sensors. Only one needs to misbehave for this issue to happen. But even with two, it is difficult to know which one is fault (for a machine). With three, it would be possible to tell. In any case, all of this is still speculation.
- losvedir 8y ago
  > MCAS will trim in increments of 10s. So it will trim, pause, trim some more, pause. No, not quite. By itself MCAS will only trim once, I believe. But if it's interrupted by a pilot manually trimming, then it will stop, wait 5 seconds, and then try to do its 10 second trim again. The characteristic up-down pattern from the Lion Air flight I think was from the latter scenario of MCAS starting to trim, the pilot manually trimming back (disabling MCAS for 5 seconds) and then it activating again. > Yes. MAX 8 has two AOA sensors. But I think the MCAS system only gets its input from one! (And it switches each flight.) If true, that's just appallingly bad.
  - outworlder 8y ago
    > No, not quite. By itself MCAS will only trim once, I believe. Under normal operation, that seems to be the case. But note that we are operating with the assumption that the AoA sensor is faulty. So it may still think the plane is in a bad attitude. > But I think the MCAS system only gets its input from one! (And it switches each flight.) If true, that's just appallingly bad. As far as public information goes, that's correct.
  - linuxftw 8y ago
    > No, not quite. By itself MCAS will only trim once, I believe. Unfortunately, we don't know this is actually true. Certainly, it's what Boeing wants us to believe, that their software is perfect in this regard. Might be completely broken. Where's the independent verification. And, allegedly, it's only supposed to trim just a little bit at each increment. If you look at the accounts, there are roller coaster-like drops. Seems to me it started nosing down really hard.
sandworm101 8y ago
>>> Pilots need to understand and know how to work with and around these systems There is a problem with the "working around" some systems. While there are definitely some situations where a pilot should bypass something, one must also look at the situations where that would be a mistake. Some systems cannot be bypassed because the chance of a pilot bypassing them in error is far greater than he or she actually needing to. For instance, asymmetric flaps. One can contrive a situation where the ability to alter flap setting asymmetrically might save an otherwise doomed aircraft (multiple control surface failures) but the risk of misusing that ability far outweighs the benefit. This anti-stall system may well have crashed these aircraft, but are there any situations where is saved an aircraft? Perhaps someone calculated that the risk of allowing pilots to bypass it outweighed the risk of it malfunctioning. Perhaps that judgement call was incorrect in this case, but I wouldn't say that pilots should always be in a position to bypass every system.
cjbprime 8y ago
> Most aircraft have 2-3 redundant systems for almost every control and feature. The 737 MAX only uses one AoA vane when deciding whether to lower the nose, so this just isn't true in the situation we're talking about.
tmd83 8y ago
At least before Lion crash it sounded like the lack of documentation or training at least wasn't exactly a mistake but a purely business decision to make it appear like the regular 737.

tim333 8y ago

>That's why I think the MCAS isn't really to blame here as much as Boeing is to blame for not properly documenting... I pretty sure the Ethiopian pilots would have been aware of the Lion Air crash and MCAS issues. The fact they still crashed suggests there's more to it.

dragontamer 8y ago
I think a wait-and-see approach is best (now that the planes are grounded). The black-box of the Ethiopian crash surely has the voice-recordings of the cockpit. So we'll be able to hear what the pilots were saying as the crash went down... we just gotta wait for the data. No point speculating when hard data is just around the corner. With the planes being grounded, there shouldn't be any safety issues if we wait.

outworlder 8y ago

> One thing to note is the mention of a "Runaway Trim Checklist". The pilots may not have recognized (in time) that it was a runaway trim issue. Many such issues involve trim being continuously applied. The trim wheel spins wildly. MCAS will trim in increments of 10s. So it will trim, pause, trim some more, pause. This may have confused the pilots. And they don't have much time to begin with – MCAS engages with autopilot off and flaps retracted. Most takeoffs have at least minimum flaps, so the plane will fly fine and then start misbehaving while still relatively close to the ground. > Most aircraft have 2-3 redundant systems for almost every control and feature. Yes. MAX 8 has two AOA sensors. Only one needs to misbehave for this issue to happen. But even with two, it is difficult to know which one is fault (for a machine). With three, it would be possible to tell. In any case, all of this is still speculation.

losvedir 8y ago
> MCAS will trim in increments of 10s. So it will trim, pause, trim some more, pause. No, not quite. By itself MCAS will only trim once, I believe. But if it's interrupted by a pilot manually trimming, then it will stop, wait 5 seconds, and then try to do its 10 second trim again. The characteristic up-down pattern from the Lion Air flight I think was from the latter scenario of MCAS starting to trim, the pilot manually trimming back (disabling MCAS for 5 seconds) and then it activating again. > Yes. MAX 8 has two AOA sensors. But I think the MCAS system only gets its input from one! (And it switches each flight.) If true, that's just appallingly bad.
- outworlder 8y ago
  > No, not quite. By itself MCAS will only trim once, I believe. Under normal operation, that seems to be the case. But note that we are operating with the assumption that the AoA sensor is faulty. So it may still think the plane is in a bad attitude. > But I think the MCAS system only gets its input from one! (And it switches each flight.) If true, that's just appallingly bad. As far as public information goes, that's correct.
- linuxftw 8y ago
  > No, not quite. By itself MCAS will only trim once, I believe. Unfortunately, we don't know this is actually true. Certainly, it's what Boeing wants us to believe, that their software is perfect in this regard. Might be completely broken. Where's the independent verification. And, allegedly, it's only supposed to trim just a little bit at each increment. If you look at the accounts, there are roller coaster-like drops. Seems to me it started nosing down really hard.

sandworm101 8y ago

>>> Pilots need to understand and know how to work with and around these systems There is a problem with the "working around" some systems. While there are definitely some situations where a pilot should bypass something, one must also look at the situations where that would be a mistake. Some systems cannot be bypassed because the chance of a pilot bypassing them in error is far greater than he or she actually needing to. For instance, asymmetric flaps. One can contrive a situation where the ability to alter flap setting asymmetrically might save an otherwise doomed aircraft (multiple control surface failures) but the risk of misusing that ability far outweighs the benefit. This anti-stall system may well have crashed these aircraft, but are there any situations where is saved an aircraft? Perhaps someone calculated that the risk of allowing pilots to bypass it outweighed the risk of it malfunctioning. Perhaps that judgement call was incorrect in this case, but I wouldn't say that pilots should always be in a position to bypass every system.

cjbprime 8y ago

> Most aircraft have 2-3 redundant systems for almost every control and feature. The 737 MAX only uses one AoA vane when deciding whether to lower the nose, so this just isn't true in the situation we're talking about.

tmd83 8y ago

At least before Lion crash it sounded like the lack of documentation or training at least wasn't exactly a mistake but a purely business decision to make it appear like the regular 737.