Duffy said a contractor was replacing ageing copper telecommunications connections with fibre-optic technology when a router began overwhelming other equipment on the air traffic control network. Investigators had not established whether the malfunction resulted from installation mistakes, operator error or defective hardware.
The contractor involved was L3Harris, which Duffy identified as an existing supplier to the FAA. He said officials were examining what happened during the maintenance work and had not reached a determination about responsibility.
The malfunction generated more than 1,000 connection attempts every four to five seconds, according to Duffy, disrupting communications with aircraft and interfering with radar feeds. The abnormal traffic spread through interconnected systems used by air traffic controllers, creating uncertainty about the reliability of information needed to manage flights.
Once technicians isolated the maintenance activity at the remote facility, the affected systems returned to service, Duffy said. That sequence led officials to believe the disruption was technical rather than malicious, although the investigation into the underlying equipment failure was continuing.
The FAA imposed its nationwide ground stop on Friday afternoon after communications and radar information became unstable at air traffic control centres and terminal radar approach facilities. The restriction prevented departures while controllers managed aircraft already airborne and brought traffic down safely.
The agency lifted the restriction at approximately 8.15pm Eastern time, allowing flights to resume gradually. However, the interruption left aircraft and crews out of position, forcing airlines to cancel services and reorganise schedules across the country.
By Saturday morning, more than 12,500 flights scheduled for Friday and Saturday had been cancelled, according to flight tracking figures. Friday accounted for more than 9,100 cancellations, with thousands more added on Saturday. The totals were expected to change as airlines adjusted their operations.
FAA Administrator Bryan Bedford said airlines expected to restore the integrity of their published schedules by the end of Sunday. That assessment depended on carriers repositioning aircraft and crews while handling passengers affected by missed connections and cancellations.
Duffy said the network was operating again but warned that restoring normal airline operations would take longer than repairing the original technical problem. Airlines were working through substantial backlogs after the suspension of departures disrupted flights throughout their networks.
Officials emphasised that the ground stop was a precaution taken because controllers could not rely consistently on communications and radar data. Duffy said roughly 3,500 aircraft were airborne when the disruption began, and established procedures were used to bring them safely to their destinations or suitable airports.
Homeland Security Secretary Markwayne Mullin said investigators had found no indication of a cyberattack. Duffy said the restoration of service after isolating the maintenance operation reinforced that assessment, while acknowledging that officials still needed to determine exactly why the router malfunctioned.
The failure has renewed scrutiny of the FAA's ageing communications infrastructure. Duffy said the equipment involved belonged to an older analogue network and that newer internet-protocol switches installed as part of the modernisation programme had continued functioning during the disruption.
He called on Congress to provide $50 billion for a comprehensive overhaul of air traffic control infrastructure, arguing that piecemeal replacement would leave critical systems vulnerable to further interruptions. The administration has already secured partial funding for modernisation, but Duffy said the larger programme remained unfinished.
The secretary distinguished the immediate repair from the broader replacement effort, saying the agency had deployed measures to reduce overload on the affected switches and routers before restoring operations. He did not announce a timetable for determining whether the contractor's installation or the replacement equipment was defective.
The incident also exposed the operational consequences of a failure affecting multiple control facilities simultaneously. Controllers at airport towers, terminal approach units and en-route centres depend on dependable communications to separate aircraft and coordinate movements. Duffy said the disruption did not eliminate every radar or telecommunications connection, but the inconsistent data made continued departures unacceptable under established safety procedures.
The FAA said the original shutdown followed intermittent telecommunications outages affecting the stability of radar and communications systems. During the stoppage, exceptions were considered for essential movements, including medical flights and other operations carrying critical supplies.
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