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WASHINGTON — Delays and cancellations among flights across the United States were minimal on Thursday, a day after a system that offers safety information to pilots failed, grounding U.S. air traffic and leading to thousands of stranded travelers.
There were 636 delays into, within or out of the U.S. as of Thursday morning, according to flight-tracking website FlightAware. There were 82 cancellations. At Salt Lake City International Airport, 16 flights into or out of the airport were delayed Thursday morning and none were canceled.
The Federal Aviation Administration said Wednesday that preliminary indications "traced the outage to a damaged database file." The agency said it would take steps to avoid another similar disruption.
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 mid-morning 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 Wednesday evening on the East Coast, according to 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 travelers could continue to see some effects "rippling through the system."
Buttigieg said his agency would now try to learn why the system went down.
According to FAA advisories, the NOTAM system failed at 8:28 p.m. 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 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 Buttigieg.
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.
The National Transportation Safety Board highlighted the large number of notices in its investigation of a near-disaster in 2017 in San Francisco. An Air Canada jet whose pilots had overlooked a NOTAM about a closed runway nearly landed by mistake on a parallel taxiway. They skimmed just over the tops of four other airliners waiting to take off.
The safety board's chairman at the time, Robert Sumwalt, noted that the closed runway was mentioned on the eighth of 27 pages of notices for the San Francisco airport, and the entry was written in an arcane fashion.
"That's what NOTAMs are. They are a bunch of garbage that no one pays any attention to," he said.
The FAA said in a 2020 report that it modernized the distribution of the notices through a standardized digital format that was to be completed in July of that year.
Contributing: Zeke Miller, Tara Copp, Kelvin Chan, Tom Krisher, Freida Frisaro
