A “corrupt system” could be to blame for the mass system failure experienced Wednesday —  resulting in flights being temporarily grounded, spurring thousands of delays  — according to reports.

The Federal Aviation Administration (FAA) announced on Wednesday afternoon that the Notice to Air Missions (NOTAM) system outage did not appear to be the result of a cyber attack, as some suspected. On the day of the outage, Transportation Secretary Pete Buttigieg said they were not yet ready to rule out nefarious activity, although he emphasized that there was no indication of that being the cause.

“The FBI has spoken to this, and of course, FAA is looking at that as well as they work to see exactly what was going on inside the files that were in the system leading to this irregularly. Again, what I would say is there’s no direct indication of any kind of external or nefarious activity. But we’re not yet prepared to rule that out,” he said at the time.

On Wednesday evening, the FAA provided another update, informing the public that it had traced the issue to a “damaged database file.”

“At this time, there is no evidence of a cyber attack,” the FAA said in the update. “We are working diligently to further pinpoint the causes of this issue and take all needed steps to prevent this kind of disruption from happening again”:

According to a report from NBC News, the system that runs NOTAM, which failed Wednesday, is 30 years old, and investigators are working to discover if the error could be traced to a contract employee who had access to the system.

Per the outlet:

Investigators are working to determine if human error or malice is to blame for taking down the system, which eight contract employees had access to. At least one, perhaps two, of those contractors made the edit that corrupted the system, two government sources said Thursday.

Transportation Secretary Pete Buttigieg told NBC News that he has asked the FAA, “to make sure that there are enough safeguards built into the system that this level of disruption can’t happen because of an individual person’s decision or action or mistake.”

According to the report, the three-decades old system is not scheduled to be updated for another six years.

Travelers walk as a video board shows flight delays and cancellations at Ronald Reagan Washington National Airport in Arlington, Va., Wednesday, Jan. 11, 2023. (AP Photo/Patrick Semansky)

Further, a report from ABC News cites a “senior official briefed on the internal review,” who asserted that an engineer “replaced one file with another.”

“It was an honest mistake that cost the country millions,” the official said, according to the outlet.

Wednesday’s outage prompted thousands of delayed U.S.-related flights that day —  10,945 — and over 1,300 cancellations. On Thursday, the FAA said operations were “back to normal”: