US officials say copper wire replacement caused national ground stop

Air travellers across the United States are facing further disruptions this weekend following a nationwide grounding of flights, just as the country prepares for the busy Thanksgiving holiday period.

Airlines are struggling to clear a backlog of delayed and cancelled services after a major air traffic control communications failure forced authorities to suspend departures across the country for about five hours on Friday, local time.

Flights have since resumed, but airlines are warning it could take days for services to return to normal.

The US government has blamed the incident on the replacement of old copper wires.

Transportation Secretary Sean Duffy told reporters on Saturday, local time, that contractor L3Harris had been replacing a section of the system's old copper wire with new fibre wire, and that work somehow caused the system overload.

Mr Duffy said the work caused "intermittent" communications and radar gaps.

He said officials were investigating whether contractor "incompetence" or a faulty router was the cause.

"Our contractor didn't meet the moment or the equipment didn't meet the moment," Mr Duffy said.

L3Harris said it took the issue seriously, and were "supporting the FAA (Federal Aviation Administration) in its investigation to understand the conditions that led to the ground stop of our nation's air travel."

L3 noted it has completed more than 70 per cent of the planned airspace communications conversion from legacy copper wires to a fibre-optic system.

Thanksgiving holiday rush

The disruption comes less than a week before the Thanksgiving travel rush, with industry group Airlines for America forecasting nearly 29 million passengers will fly on US airlines between November 20 and 30.

While officials expect operations to return to normal before the holiday rush, Mr Duffy warned that the process would be gradual.

Thousands of flights were cancelled or delayed, leaving passengers stranded at airports across the country and forcing airlines to rearrange aircraft and crew schedules.

Nearly 10,000 flights had been cancelled during the disruption, including more than 2,200 each at Delta Air Lines and American Airlines, and 1,800 at United Airlines, according to flight-tracking website Flightradar24.

Some aircraft at major airports were forced to wait more than five hours for a gate, the website reported.

US airlines will not be required to compensate stranded passengers because the disruption was caused by failures in the Federal Aviation Administration's systems rather than the carriers themselves.

The grounding was lifted at 8:15pm Eastern Time on Friday after technicians restored the affected systems.

Mr Duffy said aging routers had become overloaded with data, causing inconsistencies in the air traffic control system.

"What we have is an incredibly old air traffic control system," he said.

"It is the old hardware that went down."

The impact extended beyond the United States, with European aviation authorities asked to suspend US-bound departures during the emergency.

The disruption also affected a small number of flights from Australia, with airlines working to clear a backlog of delayed services.

The Australian Travel Industry Association warned that disruption to domestic flights within the US could continue for at least 24 hours.

It advised Australians travelling within the next 72 hours to contact their airline or travel agent if they had not received an update.

The grounding was the longest nationwide shutdown of US flight departures since the September 11 terrorist attacks in 2001.

It was only the second nationwide groundstop since those attacks, following a computer system failure in January 2023 that halted domestic departures for about 90 minutes.

US Homeland Security Secretary Markwayne Mullin said there was no evidence of a cyber-attack and sought to reassure passengers about the safety of air travel.