Aviation authorities were forced to temporarily ground all domestic flights across the United States on Wednesday due to a crucial alert system outage, triggering thousands of delays and cancellations.
The Federal Aviation Administration said normal operations were being restored but the early morning halt created knock-on effects that snarled travel throughout the day.
The grounding order was issued after the FAA identified an issue with the Notice to Air Missions system (NOTAM), which provides information to pilots about hazards, changes to airport facilities and information that can affect flights.
The agency tweeted that it was still investigating the cause of the problem.
But the outage spelled yet another hellish day for US travelers -- less than a month after a bad winter storm roiled the system.
"I just learned that my flight was delayed again," said Vince Hamilton, who was at Reagan National Airport near Washington seeking to travel to Chicago, and then on to St. Louis -- where, he said, "I have to catch a bus that I'm probably going to miss."
The nationwide halt was believed to be the first such stop order since the attacks of 9/11, according to aviation experts cited in US media. The FAA did not respond to queries seeking confirmation.
Near 2145 GMT, more than 1,300 flights within, into or out of the United States had been canceled, with more than 9,000 suffering delays, according to flight tracking website Flight Aware.
The difficulties sparked fresh criticism on Capitol Hill and throughout Washington of the FAA, which has had no confirmed administrator since March.
- Cause unknown -
The FAA reported the problem on Twitter at 6:29 am EST (1129 GMT), saying it was working to restore the NOTAM system, before announcing 50 minutes later that it ordered a pause on all domestic departures until 9:00 am.
Flying experts say the system in question contains a range of highly relevant details, such as a closed runway, to less significant matters, like the presence of a crane somewhere in or near the airport.
About 30 minutes after the FAA lifted the stop order, a screen at Reagan National Airport was overwhelmingly red with flight delays and just a handful of departures.
"Customers may continue to see some delays and cancellations as we work to restore our schedule," United Airlines said shortly after the stop order was lifted, adding it would refund customers who no longer wished to travel.
Transportation Secretary Pete Buttigieg said on MSNBC that there was no evidence of a "nefarious" cause to the attack -- but that it could not yet be ruled out.
Noting that the FAA systems have backup, Buttigieg said the inquiry would look at "why with all that redundancy it still rose to the level where that there had to be a ground stop lasting about an hour and a half, and all the delays we saw."
White House Press Secretary Karine Jean-Pierre said at a briefing that the halt was out of "an abundance of caution" due to safety risks.
Senator Maria Cantwell, the Democratic Chair of the Senate Commerce Committee, also vowed to shed light on the incident.
"We will be looking into what caused this outage and how redundancy plays a role in preventing future outages. The public needs a resilient air transportation system," Cantwell said.
Republican Senator Ted Cruz of Texas said the "completely unacceptable" outage "highlights why the public needs a competent, proven leader with substantive aviation experience leading the FAA."
The White House last week renominated Phillip Washington as chief of the aviation safety regulator, replacing former head Stephen Dickson, who left office on March 31.
Washington was originally nominated in July, but the Senate did not schedule a confirmation hearing, with some lawmakers questioning his lack of background in aviation.
Washington served as head of Denver International Airport in 2021 after a long US Army career followed by other non-aviation transportation posts.
Travel industry officials said Wednesday's crisis points to key vulnerabilities in US infrastructure.
"Today's FAA catastrophic system failure is a clear sign that America's transportation network desperately needs significant upgrades," said US Travel Association President Geoff Freeman.
The halt comes in the wake of a large-scale aviation meltdown in the United States over the Christmas holiday, as a storm brought unseasonably cold temperatures and travel chaos to the majority of the country.
Hard-hit Southwest Airlines canceled more than 15,000 flights over eight days after what it said was a breakdown in its scheduling systems. That mishap is also expected to be spotlighted in congressional hearings.