> Given that the system could not reconcile the error, the fail-safe software logic intervened to prevent the incorrect data being passed to air traffic controllers, and the FPRSA-R primary system – as designed – suspended its functioning and handed its tasks to a back-up system. But the back-up system applied the same logic to the flightplan, with the same result, and similarly suspended itself.<p>This seems to be the root cause. My reading of this is that the system initially validated the flight plan, but while processing the plan it hit something it didn’t understand. It should have treated this as a late validation error, rejected the plan and continued its work, but instead it treated it as an internal error and crashed. I guess it probably hit some kind of assertion.