Thousands of flights across the US were cancelled or delayed after a system that offers safety information to pilots failed.
The government launched an investigation into the breakdown, which grounded some planes for hours.
The Federal Aviation Administration (FAA) said preliminary indications “traced the outage to a damaged database file”.
The agency said it would take steps to avoid another similar disruption.
Safety is always our first priority, and ensuring flight safety was the reason for this morning’s ground stop while the affected systems were restored and checked. As normal flight operations have resumed, FAA continues to assess the causes of the outage. pic.twitter.com/JhsYKBDney
Advertisement— Secretary Pete Buttigieg (@SecretaryPete) January 11, 2023
The breakdown showed how much American air travel depends on the computer system that generates alerts called NOTAMs — or Notice to Air Missions.
Before a plane takes off, pilots and airline dispatchers must review the notices, which include details about bad weather, runway closures or other temporary factors that could affect the flight. The system was once telephone-based but moved online years ago.
The system broke down late Tuesday and was not fixed until midmorning on Wednesday.
The FAA took the rare step of preventing any planes from taking off for a time, and the cascading chaos led to more than 1,300 flight cancellations and 9,000 delays by early evening on the East Coast, according to flight-tracking website FlightAware.
Transportation Secretary Pete Buttigieg told a news conference that the problems “led to a ground stop because of the way safety information was moving through the system”.
After the failures were fixed, he warned that travellers could continue to see some effects “rippling through the system”.
Mr Buttigieg said his agency would now try to learn why the system went down.
Longtime aviation insiders could not recall an outage of such magnitude caused by a technology failure. Some compared it in scope to the nationwide shutdown of airspace after the 2001 terrorist attacks.
At my direction, FAA is continuing its system review. Preliminary work has traced the issue to a damaged database file, with no evidence of a cyber attack.
FAA will continue its work to further pinpoint the sources of this issue and steps to prevent it from occurring again.— Secretary Pete Buttigieg (@SecretaryPete) January 11, 2023
“Periodically there have been local issues here or there, but this is pretty significant historically,” said Tim Campbell, a former senior vice president of air operations at American Airlines and now a consultant in Minneapolis.
Mr Campbell said there has long been concern about the FAA’s technology, and not just the NOTAM system.
Many of those systems “are old mainframe systems that are generally reliable, but they are out of date,” he said.
According to FAA advisories, the NOTAM system failed at 8.28pm on Tuesday, preventing new or amended notices from being distributed to pilots.
The FAA resorted to a telephone hotline to keep departures flying overnight, but as air traffic picked up in the morning, the phone system was overwhelmed.
The FAA ordered all departing flights grounded early on Wednesday, affecting all passenger and cargo flights. Some medical flights could get clearance, and the outage did not affect military operations.
President Joe Biden said that he was briefed by Mr Buttigieg.
Mr Buttigieg said the ground stop showed that “safety is going to be our North Star, as it always is”.
“We are now pivoting to focus on understanding the causes of the issue,” he said.
Pilots and safety officials have complained about NOTAMs for years, saying there are too many of them and that some are unnecessary and written in cryptic abbreviations.
