As described in the Software Failure, the cause of the 2004 LA Air Traffic Control incident was
◦ human error
◦ the fact that the system had not been rebooted within 50 days
◦ the fact that it takes just under 50 days for the countdown timer to count down four billion milliseconds and the subsystem shuts down when it reaches zero
◦ there was no software patch to automatically reset the countdown timer without human intervention
◦ all of these