Originally Posted by
MechEngr
It should have an independent watchdog timer processor to automatically reboot if there is a fundamental software failure, but maybe only the thread/task/subsystem to update the displays failed and the watchdog reset and all other controls is still running
The fact that "all six DUs stayed blank
until a different runway was selected" suggests it wasn't dead, just thinking.
I recall a widely-distributed maths library function that could take literally years to execute with certain near-zero inputs. Could be something like that.