According to the diagrams in US patent 7,852,235 [1], the FCC-730 CPU is an FCP-2002. I would caution against the possibly mistaken inference that this patent describes the actual architecture of the 737-MAX or any other actual flight computer, as opposed to simply a design that Rockwell-Collins may have developed and not (yet) actually deployed. In particular, while the 737-MAX does have an FCC-730, I don't think it has an IPS-5000.
A NASA Langley presentation [2] mentions formal verification of the FCP-2002. I think that if it is formally verified, it is probably not a 286. A 286 would be a poor choice for a formally verified microprocessor for embedded applications since it has a huge number of extraneous features that would complicate the verification process while yielding no benefit for the embedded application. The presentation also mentions a new "FCS 5000" product line, and its formal verification, and I wonder if that has any connection with the IPS-5000 CPU card mentioned in the patent diagram? Probably, the patent describes a new flight control computer design, meant as a successor to the design used in the 737-MAX (and other Boeing aircraft such as the 777).
The Boeing 777 autopilot uses FCP 2002 CPUs as well [3]
I swear I read somewhere that the FCP 2002 had a stack machine architecture, but now I can't find where I read that. (Did I imagine reading it?)
I'm not sure where this "286" stuff comes from. I think maybe, FCP-2002 is a 16-bit CPU, and then people say a 16-bit CPU is "like a 286", and then maybe that gets corrupted in the retelling, and "like a 286" turns into "a 286"?
[1] https://patents.google.com/patent/US7852235B1
[2] https://shemesh.larc.nasa.gov/NFM2018/talks/Butler.pdf
[3] https://web.archive.org/web/20100822151603/http://www.rockwe...