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What is more worrying for Boeing is that a SW fix might not be that easy to implement. According to that article [0], the fix is running too slowly on the Flig

by seren 7y ago

What is more worrying for Boeing is that a SW fix might not be that easy to implement. According to that article [0], the fix is running too slowly on the Flight Control Computers, that are based on a 80286 architecture. I am not sure how reliable this info is, and that should not be surprising given the cost of verification or certification of an aircraft, but I am still surprised that a 2019 plane, has still some HW and SW from the 1980ies. Edit : There are actually more details in Wikipedia [1] >In June 2019, "in a special Boeing simulator that is designed for engineering reviews"[75], FAA pilots performed a stress testing scenario – an abnormal condition identified through FMEA after the MCAS update was implemented[76] – for evaluating the effect of a fault in a microprocessor: as expected from the scenario, the horizontal stabilizer pointed the nose downward. Although the test pilot ultimately recovered control, the system was slow to respond to the proper runaway stabilizer checklist steps, due to an 80286[77] microprocessor being overwhelmed with data. The FAA characterized the slow responsiveness as "catastrophic", whereas Boeing initially classified it as "major". The solution appears to consist in rerouting data across multiple chips. Boeing stated that the issue can be fixed in software.[78] The software change will not be ready for evaluation until at least September 2019.[79] Boeing also said that it agreed with additional requirements that the FAA required it to fulfill, and added that it was working toward resolving the safety risk. It will not offer the MAX for certification until all requirements have been satisfied.[80] [0] https://www.moonofalabama.org/2019/06/boeings-software-fix-for-the-737-max-problem-overwhelms-the-planes-computer.html https://www.moonofalabama.org/2019/06/boeings-software-fix-f... [1] https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au...

0815test 7y ago
> According to that article, the fix is running too slowly on the Flight Control Computers, that are based on a 80286 architecture. See, that's the nice thing. All they have to do is push the Turbo button, it will work like a charm.
tempguy9999 7y ago
Possibly talking rubbish but: a 286 is simple, well understood both in terms of its spec and its performance (no fancy pipelines, no cache, so very predictable performance), is fabbed probably in the order of a micrometer so highly resistant to cosmic rays (assuming CRs do affect circuitry), inerface to memory that is equally 'boring', those 286s are perhaps hardened and quite possibly still produced for this purpose. All the above is speculation but I can imagine that I'd like very old, boring, predictable and very understood tech rather than the latest. That said, it is a bit unexpected.
- Leherenn 7y ago
  It's probably also certified, and has been in the 737 for a very long time. Usually, if you see something old in a plane it's a matter of certification as it's a long and really, really expensive process. If the chip has enough power to do what is needed, the only reason to change it is that procurement for new parts become more expensive than recertification. Given the price of certification, companies make sure these parts remain available for decades as that's still cheaper.
  - tempguy9999 7y ago
    expensive, yah. After I posted I did a little digging. "The RAD750 is a radiation-hardened single board computer manufactured by BAE" and "The RAD750 system has a price that is comparable to the RAD6000 which is US$200,000 per board (per 2002 reference)" <https://en.wikipedia.org/wiki/RAD750> https://en.wikipedia.org/wiki/RAD750> More general info here, inc. use of an 8086 and a MIPS R3000: "The CPUs of Spacecraft Computers in Space" <http://www.cpushack.com/space-craft-cpu.html> http://www.cpushack.com/space-craft-cpu.html> which backs up the chip cost mentioned above. Generally interesting. Completely agree that if it's fast enough, why change it.
kova12 7y ago
Perhaps they should replace it with raspberry pi or something...

by seren 7y ago

0815test 7y ago

> According to that article, the fix is running too slowly on the Flight Control Computers, that are based on a 80286 architecture. See, that's the nice thing. All they have to do is push the Turbo button, it will work like a charm.

tempguy9999 7y ago

Possibly talking rubbish but: a 286 is simple, well understood both in terms of its spec and its performance (no fancy pipelines, no cache, so very predictable performance), is fabbed probably in the order of a micrometer so highly resistant to cosmic rays (assuming CRs do affect circuitry), inerface to memory that is equally 'boring', those 286s are perhaps hardened and quite possibly still produced for this purpose. All the above is speculation but I can imagine that I'd like very old, boring, predictable and very understood tech rather than the latest. That said, it is a bit unexpected.

Leherenn 7y ago
It's probably also certified, and has been in the 737 for a very long time. Usually, if you see something old in a plane it's a matter of certification as it's a long and really, really expensive process. If the chip has enough power to do what is needed, the only reason to change it is that procurement for new parts become more expensive than recertification. Given the price of certification, companies make sure these parts remain available for decades as that's still cheaper.
- tempguy9999 7y ago
  expensive, yah. After I posted I did a little digging. "The RAD750 is a radiation-hardened single board computer manufactured by BAE" and "The RAD750 system has a price that is comparable to the RAD6000 which is US$200,000 per board (per 2002 reference)" <https://en.wikipedia.org/wiki/RAD750> https://en.wikipedia.org/wiki/RAD750> More general info here, inc. use of an 8086 and a MIPS R3000: "The CPUs of Spacecraft Computers in Space" <http://www.cpushack.com/space-craft-cpu.html> http://www.cpushack.com/space-craft-cpu.html> which backs up the chip cost mentioned above. Generally interesting. Completely agree that if it's fast enough, why change it.

kova12 7y ago

Perhaps they should replace it with raspberry pi or something...