9 ms·

MCAS is a band-aid trying to fix the inherent stability of the 737 max. Add in the fact that a single faulty pitch sensor could bring down a plane and blam. F

MCAS is a band-aid trying to fix the inherent stability of the 737 max. Add in the fact that a single faulty pitch sensor could bring down a plane and blam. Finally, fail to properly train pilots on how the system actually worked and how to override it and here we are today. Software is a part of it but overall I don't see it as a software issue.

babesh 7y ago
I think it was a systems issue with the software a part of it. From what I read, the software system is archaic in a bad way since you have duplicate systems but not used for redundancy. Only one set is used at a time and which one is switched with every boot. It had two pitch sensors but each is paired with a single computer. There was an optional add on to use both sensors in some way but this is unreliable as well since you don’t know which is right. It was when the plane was flying with the failed sensor (every other time since only one sensor failed) that they ran into the problem. At least from my readings of how you are supposed to build robust systems from unreliable parts, this is a terrible way to design a system. See https://www.seattletimes.com/business/boeing-aerospace/faa-cautions-airlines-on-maintenance-of-sensors-that-were-key-to-737-max-crashes/ https://www.seattletimes.com/business/boeing-aerospace/faa-c... for info on the sensors. Search for Jim Gray and fault tolerance on how to build reliable systems from unreliable parts. You need redundant parts with voting (which implies more than 2 sensors and more than 2 computers), error detection, etc... Supposedly the Space Shuttle computer systems were designed right although much of the rest of the Shuttle wasn’t designed right. The Boeing way relied on the pilots to compensate for mechanical or software failure. Unfortunately, they seemed to willingly choose to not inform pilots of MCAS and there seemed to be failure scenarios where recovery is difficult. Lastly, I think it is part of the job of a software engineer to push back on requirements and designs that don't work even if it is a failure in the system. Falling back to built as spec'd isn't worth of being called engineering.

babesh 7y ago

I think it was a systems issue with the software a part of it. From what I read, the software system is archaic in a bad way since you have duplicate systems but not used for redundancy. Only one set is used at a time and which one is switched with every boot. It had two pitch sensors but each is paired with a single computer. There was an optional add on to use both sensors in some way but this is unreliable as well since you don’t know which is right. It was when the plane was flying with the failed sensor (every other time since only one sensor failed) that they ran into the problem. At least from my readings of how you are supposed to build robust systems from unreliable parts, this is a terrible way to design a system. See https://www.seattletimes.com/business/boeing-aerospace/faa-cautions-airlines-on-maintenance-of-sensors-that-were-key-to-737-max-crashes/ https://www.seattletimes.com/business/boeing-aerospace/faa-c... for info on the sensors. Search for Jim Gray and fault tolerance on how to build reliable systems from unreliable parts. You need redundant parts with voting (which implies more than 2 sensors and more than 2 computers), error detection, etc... Supposedly the Space Shuttle computer systems were designed right although much of the rest of the Shuttle wasn’t designed right. The Boeing way relied on the pilots to compensate for mechanical or software failure. Unfortunately, they seemed to willingly choose to not inform pilots of MCAS and there seemed to be failure scenarios where recovery is difficult. Lastly, I think it is part of the job of a software engineer to push back on requirements and designs that don't work even if it is a failure in the system. Falling back to built as spec'd isn't worth of being called engineering.