"The fault occurs when bits inside the microprocessor are randomly flipped from 0 to 1 or vice versa. This is a known phenomenon that can happen due to cosmic rays striking the circuitry."
This is called Single Event Upset. For all those of you that aren't in the industry, essentially the problem is that any bit inside the flight computer (RAM, cache, NVM, registers - ANY bit) can change state randomly at ANY time. It's rare, but when you get into millions of flight hours, it WILL happen. The software and hardware have to be designed to mitigate problems caused by this behavior.
This is called Single Event Upset. For all those of you that aren't in the industry, essentially the problem is that any bit inside the flight computer (RAM, cache, NVM, registers - ANY bit) can change state randomly at ANY time. It's rare, but when you get into millions of flight hours, it WILL happen. The software and hardware have to be designed to mitigate problems caused by this behavior.