CNN
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Officials are still trying to figure out exactly what led to the Federal Aviation Administration system outage on Wednesday but have traced it to a corrupt file, which was first reported by CNN.

In a statement late Wednesday, the FAA said it was continuing to investigate the outage and “take all needed steps to prevent this kind of disruption from happening again.”

“Our preliminary work has traced the outage to a damaged database file. At this time, there is no evidence of a cyberattack,” the FAA said.

The FAA is still trying to determine whether any one person or “routine entry” into the database is responsible for the corrupted file, a government official familiar with the investigation into the NOTAM system outage told CNN.

Another source familiar with the Federal Aviation Administration operation described exclusively to CNN on Wednesday how the outage played out.

When air traffic control officials realized they had a computer issue late Tuesday, they came up with a plan, the source said, to reboot the system when it would least disrupt air travel, early on Wednesday morning.

But ultimately that plan and the outage led to massive flight delays and an unprecedented order to stop all aircraft departures nationwide.

The computer system that failed was the central database for all NOTAMs (Notice to Air Missions) nationwide. Those notices advise pilots of issues along their route and at their destination. It has a backup, which officials switched to when problems with the main system emerged, according to the source.

FAA officials told reporters early Wednesday that the issues developed in the 3 p.m. ET hour on Tuesday.

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.

In the overnight hours of Tuesday into Wednesday, FAA officials decided to shut down and reboot the main NOTAM system – a significant decision, because the reboot can take about 90 minutes, according to the source.

They decided to perform the reboot early Wednesday, before air traffic began flying on the East Coast, to minimize disruption to flights.

“They thought they’d be ahead of the rush,” the source said.

During this early morning process, the FAA told reporters that the system was “beginning to come back online,” but said it would take time to resolve.

The system, according to the source, “did come back up, but it wasn’t completely pushing out the pertinent information that it needed for safe flight, and it appeared that it was taking longer to do that.”

That’s when the FAA issued a nationwide ground stop at around 7:30 a.m. ET, halting all domestic departures.

Aircraft in line for takeoff were held before entering runways. Flights already in the air were advised verbally of the safety notices by air traffic controllers, who keep a static electronic or paper record at their desks of the active notices.

Transportation Secretary Pete Buttigieg ordered an after-action review and also said there was “no direct evidence or indication” that the issue was a cyberattack.

The source said the NOTAM system is an example of aging infrastructure due for an overhaul.

“Because of budgetary concerns and flexibility of budget, this tech refresh has been pushed off,” the source said. “I assume now they’re going to actually find money to do it.”

“The FAA’s infrastructure is a lot more than just brick and mortar.”

Investment in the agency is set to be addressed this year by Congress when the five-year FAA Reauthorization Act signed in 2018 expires.