Catastrophic FAA outage traced back to tiny mistake by one engineer: report
Southwest Airlines Boeing 737 with the new livery landing at the Fort Lauderdale/Hollywood International Airport. (Carlos Yudica / Shutterstock.com)

On Wednesday, ABC News' Josh Margolin reported that the cause of today's catastrophic flight system failure, which paralyzed the Federal Aviation Administration and led to the first nationwide ground stop of all aircraft in the United States since the September 11 terrorist attacks, has been identified.

The source of the problem was reportedly a single engineer who made a small mistake with a file transfer.

"The ground stop and FAA systems failures this morning appear to have been the result of a mistake that that occurred during routine scheduled maintenance, according to a senior official briefed on the internal review," reported Margolin. "An engineer 'replaced one file with another,' the official said, not realizing the mistake was being made Tuesday. As the systems began showing problems and ultimately failed, FAA staff feverishly tried to figure out what had gone wrong. The engineer who made the error did not realize what had happened."

The mistake ultimately led to a total shutdown of Notice to Air Missions (NOTAM), the system that sends critical notifications to pilots, delaying flights all over the country.

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"It was an honest mistake that cost the country millions," one official told ABC.

The massive disruption to the air traffic system comes just weeks after a meltdown at Southwest Airlines, where a combination of ground crew workers pushed to breaking point in the middle of deep freeze conditions and the collapse of an antiquated scheduling system used since the 1990s led to the mass cancelations of flights.