Simple question: Why doesn't Boeing upgrade to i386 for their new planes? I heard it's available for aerospace applications.
(One thing that springs to mind was that the way addresses running past the end of a segment worked was different)
Note: this is not necessarily a stupid decision.
If you think they are at best 40 MHz 286 parts, the best that was available by then, running software derived from previous releases that ran on slower chips, there is plenty of room for improvement.
IIRC, you can get a modern 65816 (the 16-bit descendant of the 6502) in 300+ MHz. And I wouldn't expect it to be on a cutting edge process.
That considered, it's entirely possible most of the time is being consumed by reading the sensors. In that case, the sensor communication would need to be upgraded and recertified.
Fun thing: I remember a 40 MHz 286 desktop at one point. Wikipedia tells me they only went to 25 MHz. That's some overclocking...
Fun fact #2: with a feature size of 1.5 µm, one could fit an entire 6502 done in 7 nm process on top of a single 80286 transistor.