Thousands of domestic US flights were delayed or cancelled on Wednesday when air authorities grounded planes following a malfunction in a key system used by pilots before take-off.
The Federal Aviation Administration, or FAA, said the disruption stemmed from problems with the Notice to Air Missions system — Notam — which conveys advisory information essential for flight operations, including alerting pilots to hazards and providing a range of updates, from information on broken equipment to airport construction.
Passengers complained on social media of flight delays and last-minute cancellations, with some saying their pilots could not gain access to flight paths.
The systems failure is one of the most significant in recent decades and comes after a year of tests for the nation’s air system, as the industry continues to deal with the fallout from the pandemic.
The cause of the malfunction was still being investigated, though the White House said there was no evidence of a cyber attack.
A trade group representing the US travel industry called the FAA system failure “catastrophic”.
“America’s transportation network desperately needs significant upgrades,” Geoff Freeman, president of the US Travel Association, said in a statement.
“We call on federal policymakers to modernise our vital air travel infrastructure.”
John Cox, a former airline pilot and aviation safety expert, said there has been talk in the aviation industry for years about modernising the Notam system, but he did not know the age of the servers that the FAA uses.
He did not rule out the possibility of a cyber attack.
“I’ve been flying 53 years. I’ve never heard the system go down like this,” Mr Cox told The Associated Press. “So something unusual happened.”
Senate Commerce Committee chairwoman Maria Cantwell said the panel would investigate the issue.
“We will be looking into what caused this power cut and how redundancy plays a role in preventing future power cut,” she said.
More than 5,400 flights were delayed and 900 cancelled, according to website FlightAware, and officials said it would take hours to recover from the incident.
By midday on Wednesday in the US, operations were getting back to normal.
Melanie Thigpen, who was heading from Atlanta to Washington, told AP that she learnt of the delays while en route to the airport.
“I really didn't know till I was on my way here that it was a big issue and then I looked it up. And then I sort of get super stressed out because, like I said, I have a meeting at 4pm and, you know, if I don't make it, I don't make it,” she said.
The Notam failure affected tens of thousands of passengers across the US, but international flights coming into the country continued to mostly operate without widespread cancellations.
A Paris airports spokeswoman said: “At this stage, there have been no flight cancellations but some delays are to be expected.”
Flights bound for the US were delayed in Madrid, Reuters reported.
The FAA's system malfunction comes weeks after an operational meltdown at Southwest at the end of last year left thousands of passengers stranded.
A severe winter storm right before Christmas, coupled with the Texas-based carrier's dated technology, led to more than 16,000 flight cancellations last month.
According to FAA advisories, the Notam system failed at 8.28pm ET on Tuesday, preventing new or amended notices from being distributed to pilots.
The FAA resorted to a telephone hotline to keep planes flying overnight, but as daytime traffic picked up, the telephone system was overwhelmed.
“Normal air traffic operations are resuming gradually across the US following an overnight power cut to the Notice to Air Missions system that provides safety info to flight crews. The ground stop has been lifted,” the FAA later announced on Twitter.
US President Joe Biden addressed the issue on Wednesday before leaving the White House, saying he had been briefed by Transport Secretary Pete Buttigieg, who told him they had still not identified what went wrong.
“I told him to report directly to me when they find out. Air traffic can still land safely, just not take off right now. We don’t know what the cause of it is,” Mr Biden said.
Agencies contributed to this report
