Couldn't a good state-run sabotage take advantage of assumptions about how much scrutiny/inspection is needed for a given component?
For example, suppose there was some little-known chemistry that would make a PCB likely to fail $X years after manufacture. Or bonus points if it had out-gassing that made other, innocent parts have high failure rates?
That's for new-manufactured boards. My guess is this whole run completed years ago. And surely new boards will be farmed out to some other Mom & Pop PCB shop. These companies are everywhere, electronics assembly is not meaningfully "high tech" any more.
For real though. They stick anything and everything interesting in FPGAs for defense aerospace.
Check out this missile guidance computer. https://www.bunniestudios.com/blog/?p=3649 Pretty much just a PowerPC and some RAM glued to a giant FPGA with a lot of off board inputs. These days they'd use something like a Zynq that has the hard processor core on the FPGA die, making it look even more like an FPGA breakout board.
Any malicious intervention would as you say have to be very subtle to pass system tests. Given they cannot know whether and when the planes would ever be used against them, it would be playing the long game at best.
I'm imaging failure cases under high Gs when the thing tries to do some high speed data transfer?
let the traces move enough to introduce cross talk if its vibrated and accelerated in just the right way.
There is a short term gain, even if they never get used against china: the US and it's allies have to spend more in testing to account for the Chinese built PCBs.
For example, suppose there was some little-known chemistry that would make a PCB likely to fail $X years after manufacture. Or bonus points if it had out-gassing that made other, innocent parts have high failure rates?