Originally Posted by
MurphyWasRight
There are vendors that specialize in supporting old ICs, they sometimes even buy the mask sets from the original vendor.
Needles to say the price is a 'bit' higher than the original but worth it compared to a full redesign.
Of course a 286 would also easily fit on a lot of FPGAs these day but cant imagine that would be any easier to certify than a clean sheet design,
This is more common than you may think - there are a lot of aircraft out there that were certified in the 1980s and early 1990s - some still in production - e.g. the 767 and 777 - and they need spares. Further, the PW4000/94" (EEC131) and CF6-80C2 (FADEC 1 on the 767) are still in production and they need parts. It's very, very expensive to certify new, from the ground up hardware for flight critical systems. So there is a lot of effort expended to keep those systems running with the various parts obsolescence issues. While certifying new 'simple' parts such as resistors is usually straight forward, any changes to logic devices - processors, FPGAs, etc. - for flight critical systems is a big deal. I certified a number of parts obsolescence changes to various FADEC boxes over the years. As Murphy notes, while the OEMs usually are not interested, other 'boutique' vendors have picked up the task of keeping those older model CPUs available - usually using modern manufacturing techniques. But things can easily go wrong - something simple like a die shrink can affect the timing margins (faster is not always better). I wasn't involved, but I recall a FPGA change to the Trent 800 FADEC maybe 20 years ago - they made it much faster, which had unexpected effects and caused the FADEC to sometimes hang up or crash. I think they were able to find enough of the old parts that they didn't effect delivers before they got it straightened out, but it was close.
No direct knowledge, but I think part of what they are struggling with on the MAX is that the system where MCAS is resident was never designed to be flight critical - I'm guessing it was Design Assurance Level (DAL C) - now since it's understood MCAS is flight critical, they're having to re-certify it as DAL A. That's a big, time consuming deal, and they are finding some unexpected items that have been there all along (without causing problems) but need to be corrected to make it DAL A.