The ground stop that brought air travel across the country to a halt Friday evening highlighted persistent weaknesses in the Federal Aviation Administration’s aging air traffic control infrastructure, which has had several disruptive failures in recent months.
Two months ago, a circuit failure and severed fiber optic cable caused crippling ground stops and delays at airports along the East Coast. Smaller outages unfolded in October at Raleigh-Durham International Airport in North Carolina and George Bush Intercontinental Airport in Houston, when contractors accidentally cut into fiber line.
The Friday ground stop, which was only the third the F.A.A. has issued this century, eclipsed the fallout of previous air traffic communications equipment failures. Officials said it was prompted by efforts to replace an outdated router, which caused circuits in the national air traffic network to become overloaded and fail, interrupting communication lines between air traffic controllers and pilots.
By Saturday, thousands of flights had been canceled, and airports were still crowded with stranded travelers. The recovery will most likely take days, as airlines rebook passengers and reposition planes.
Friday’s breakdown, and the earlier episodes, have underscored the structural vulnerabilities that hamper controllers’ ability to safely manage flight traffic, even after improvements. And they have raised questions about whether federal authorities have done enough to create backup systems to prevent disruptive or catastrophic failures.
Friday’s incident touched off a blame game in Washington. Sean Duffy, the transportation secretary, accused Congress of failing to pony up for systemwide upgrades.
“How many more times does this have to happen for Congress to give the money to fix it?” he asked reporters at the White House.
He demanded that lawmakers approve $50 billion in emergency funds for the project, tens of billions more than he had previously requested. He did not explain how the money would be spent, but said that his department had been forced to pursue insufficient patchwork upgrades.
Last year, Congress gave the F.A.A. $12.5 billion to fuel its air traffic modernization plan. But according to a September report from the Government Accountability Office, the F.A.A. was juggling 11,389 modernization projects that had not been integrated, predicting that a lack of better coordination would “increase the likelihood of F.A.A. repeating its history of cost overruns, delays and unmet performance targets.”
Congressional aides say that lawmakers in both parties have also expressed skepticism about Mr. Duffy’s use of the appropriated money, including whether it is being spent efficiently.
For decades, air traffic communications have relied on a system that runs on analog copper wire, floppy disks and alphabetical keyboards so old that the F.A.A. has difficulty sourcing spare parts. Congress approved its first tranche of modernization funds after faulty equipment caused a series of outages in traffic control facilities, including the one serving Newark Liberty International Airport, leading to alarming losses of radar and other communications capabilities.
Earlier this month, L3 Harris, the primary telecommunications contractor tasked with managing the system upgrades, said on its website that it had converted about 70 percent of the copper line to fiber optic cable. And last week, the F.A.A. announced it would begin to phase out floppy disks.
In a statement, L3 Harris said that it was supporting the F.A.A. in its investigation of what led to Friday’s meltdown, and that it “takes the nationwide ground stop and its impact on travelers, airlines and air traffic operations seriously.”
The disruptions in recent weeks have also revealed that even the upgrades the F.A.A. has made have sometimes had serious vulnerabilities.
In September, when a circuit at a regional air traffic facility failed, operators had no backup options beyond the fiber line, 600 feet of which they discovered had been severed by a construction crew in New Jersey working on an Amtrak project. More than 430 flights were canceled before the system was fixed several hours later.
A similar incident occurred in October at Raleigh-Durham International Airport, when a plumbing contractor accidentally severed a fiber line. The airport was forced to issue a ground stop for several hours. A day later, officials were forced to issue a ground stop at George Bush Intercontinental Airport, when another contractor inadvertently severed a fiber line.
Bryan Bedford, the F.A.A. administrator, told reporters at the time that the fiber line upgrades were not enough to save the system from failure. And the F.A.A. had yet to incorporate the sort of cloud services that could provide additional redundancies.
“There’s no backup to the backup,” he told reporters at a Saturday news conference.
Since last year, Mr. Duffy’s requests for air traffic funding have crept up. After Congress approved $12.5 billion in air traffic modernization last year — $7.75 billion of which was dedicated to telecommunications and radar upgrades — Mr. Duffy said publicly that he would need another $19 to $20 billion to complete the work.
But earlier this year, he began asking lawmakers to approve $30 billion in additional spending, only a third of which would be dedicated exclusively to air traffic control modernization. Under legislation shaped by his thinking, $10 billion would go toward airport beautification projects, while another $10 billion would go to general improvements in towers, terminals and airports. The Senate and House versions of it do not have any cosponsors.
On Saturday, Mr. Bedford told reporters that the F.A.A. likely needed an infusion of “about $10.1 billion to finish modernization.” He added that the agency had committed about 38 percent of the $12.5 billion that Congress provided last year. That pace, he said, was in keeping with the agency’s plans to complete funded projects by the end of 2028.
He did not endorse Mr. Duffy’s call for $50 billion in funding, or attempt to itemize what the full amount could pay for. He also did not echo the secretary’s insistence that Congress provide that windfall before the end of the year.
Mr. Duffy’s request on Friday that Congress approve emergency funding reflected a looming political reality for the Trump administration. In January, when Democrats assume control of the House and Senate, it may be more difficult for the administration to secure new funding.
Late Friday night, Representative Hakeem Jeffries of New York, the Democratic minority leader, made clear that he did not accept Mr. Duffy’s argument that inadequate congressional funding was to blame for incidents like Friday’s meltdown.
The ground stop, he said, was “the latest in a series of unacceptable air travel incidents under the Trump administration’s failed leadership.”