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You would think it would make sense to automatically disable the MCAS system and sound a warning if the aircraft detects conflicting readings from it's sensors

You would think it would make sense to automatically disable the MCAS system and sound a warning if the aircraft detects conflicting readings from it's sensors.

ams6110 8y ago
Yes, especially since there are only 2 AOA sensors so you can't know which one is incorrect by comparing to a third sensor. I've read that it's possible to derive AOA from other sensors but don't think these aircraft have that ability.
- heyjudy 8y ago
  Serious lack of redundancy in a life-safety critical-system. It should have: - 5+ AOA sensors of different types - discard any sensor values that are stuck or providing incorrect readings - have a spray, heating system (some do) and camera system for automatically deicing and verifying AOA sensors in-flight Without a camera system to verify sensors, crews won't have a definitive way to know if they're getting true or false information from clogged pitot, stuck AOA or malfunction.
  - deleted 8y ago
    [deleted]
- kwhitefoot 8y ago
  You should always have at least three and preferably an odd number of similar sensors so that you can get at least a vague idea of consensus. The British Royal Navy rule was: take one chronometer or three, never two because with two you will always be unsure which one is correct while with three you can, usually, just average the two that are closest together and regard the third as an outlier. See also https://blog.ipspace.net/2017/01/never-take-two-chronometers-to-sea.html https://blog.ipspace.net/2017/01/never-take-two-chronometers...
akira2501 8y ago
Due to the way the engines are mounted on the frame, which enhances their efficiency, they also cause more of a "upward thrust vector." This makes it very easy for this plane to reach dangerously high AOA in certain scenarios, particularly during turns. The MCAS has a specific and important function and just turning it off is probably not going to increase safety. The real problem was the Boeing did not disclose the existence of this device and it's functions in aircraft training, according to one source, because they did not want to inundate new pilots with too much information about the plane and it's attendant safety systems. Perhaps, had the pilots known, they would have seen the stick shaker/stall warning system activating on _one side only_ as a serious indication of an Airspeed/AOA system fault and the potential for incorrect MCAS outputs being generated. They might have known to disable the electronic trim control, bypassing the MCAS, and then to manually fly and trim the plane with the aforementioned thrust vectoring taken into consideration. They could have trained for this. That would have all given them the best safety margin for survival here.
- anoncoward111 8y ago
  And yet it didn't happen, because of corporate bloat, inefficiency, and most likely greed. "The planes sell themselves! Let the air companies figure out how to fly them." -Boeing executives, probably.
  - johnnylambada 8y ago
    As a former Boeing software engineer (not on the commercial plane side) I can say without any hesitation that you're completely wrong in your description of what goes on at Boeing. The "bloat" you speak of is the very reason we are not subjected to many more tragedies like this. Safety takes time and people.
    - anoncoward111 8y ago
      Why roll out a change without notifying someone? Why make systems more complex when miscommunication results in death? This isn't to say that manual, mechanic controls are better that automated electronic ones. Indeed the Air France crash from Brazil was mechanical pilot error. But for me it is not sufficient to say "we do a really good job and have a lot of safety protocols." The training either was communicated or wasn't.

You would think it would make sense to automatically disable the MCAS system and sound a warning if the aircraft detects conflicting readings from it's sensors.

ams6110 8y ago

Yes, especially since there are only 2 AOA sensors so you can't know which one is incorrect by comparing to a third sensor. I've read that it's possible to derive AOA from other sensors but don't think these aircraft have that ability.

heyjudy 8y ago
Serious lack of redundancy in a life-safety critical-system. It should have: - 5+ AOA sensors of different types - discard any sensor values that are stuck or providing incorrect readings - have a spray, heating system (some do) and camera system for automatically deicing and verifying AOA sensors in-flight Without a camera system to verify sensors, crews won't have a definitive way to know if they're getting true or false information from clogged pitot, stuck AOA or malfunction.
- deleted 8y ago
  [deleted]
kwhitefoot 8y ago
You should always have at least three and preferably an odd number of similar sensors so that you can get at least a vague idea of consensus. The British Royal Navy rule was: take one chronometer or three, never two because with two you will always be unsure which one is correct while with three you can, usually, just average the two that are closest together and regard the third as an outlier. See also https://blog.ipspace.net/2017/01/never-take-two-chronometers-to-sea.html https://blog.ipspace.net/2017/01/never-take-two-chronometers...

akira2501 8y ago

Due to the way the engines are mounted on the frame, which enhances their efficiency, they also cause more of a "upward thrust vector." This makes it very easy for this plane to reach dangerously high AOA in certain scenarios, particularly during turns. The MCAS has a specific and important function and just turning it off is probably not going to increase safety. The real problem was the Boeing did not disclose the existence of this device and it's functions in aircraft training, according to one source, because they did not want to inundate new pilots with too much information about the plane and it's attendant safety systems. Perhaps, had the pilots known, they would have seen the stick shaker/stall warning system activating on _one side only_ as a serious indication of an Airspeed/AOA system fault and the potential for incorrect MCAS outputs being generated. They might have known to disable the electronic trim control, bypassing the MCAS, and then to manually fly and trim the plane with the aforementioned thrust vectoring taken into consideration. They could have trained for this. That would have all given them the best safety margin for survival here.

anoncoward111 8y ago
And yet it didn't happen, because of corporate bloat, inefficiency, and most likely greed. "The planes sell themselves! Let the air companies figure out how to fly them." -Boeing executives, probably.
- johnnylambada 8y ago
  As a former Boeing software engineer (not on the commercial plane side) I can say without any hesitation that you're completely wrong in your description of what goes on at Boeing. The "bloat" you speak of is the very reason we are not subjected to many more tragedies like this. Safety takes time and people.
  - anoncoward111 8y ago
    Why roll out a change without notifying someone? Why make systems more complex when miscommunication results in death? This isn't to say that manual, mechanic controls are better that automated electronic ones. Indeed the Air France crash from Brazil was mechanical pilot error. But for me it is not sufficient to say "we do a really good job and have a lot of safety protocols." The training either was communicated or wasn't.