“Officials ultimately found a corrupt file in the main NOTAM system, the source told CNN. A corrupt file was also found in the backup system.”
One damaged database file stopped every domestic departure in the US. The backup had the same corruption, so it was a copy, not a backup. The FAA rebooted overnight to get ahead of the rush, and the system came back unable to push the safety notices pilots need. Planes already in the air got their notices read aloud by controllers working from paper records.